Climate Change and the Power Industry - a Literature Research

Climate Change And The Power Industry - A Literature Research -

by Dr. rer. nat. Rüdiger Beising October 2006 1st Revision, March 2007

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3 Table of contents

Preface / Summary 7 1 The Climate of the Earth 18 1.1 Atmosphere 18 1.2 Hydrosphere 20 1.3 Cryosphere 21 1.4 Geosphere 21 1.5 Biosphere 21 2 The Carbon Dioxide Circulation 23 2.1 Geosphere 24 2.2 Ocean 24 2.3 Atmosphere 25 2.4 Biosphere 25 3 The Radiation Budget and the Greenhouse Effect 27 3.1 Radiation Balance 27 3.2 Radiative Forcing 28 3.3 The Greenhouse Effect 29 4 Natural Influencing Factors on the Climate 33 4.1 The Sun 33 4.1.1 Solar Radiation 34 4.1.2 Cosmic Particle Radiation and Geomagnetic Field 38 4.2 Volcanoes 41 4.3 North Atlantic Oscillation - NAO 43 4.4 Southern Oscillation El Niño – ENSO 46 4.5 Thermohaline Circulation (THC) 47 4.6 Natural Greenhouse Gases 49 5 Anthropogenic Influencing Factors on the Climate 50 5.1 Anthropogenic Greenhouse Gases 50 5.1.1 Water Vapour (H2O) 54 5.1.2 Carbon Dioxide (CO2) 55 5.1.3 Methane (CH4) 57 5.1.4 Nitrous Oxide (N2O) 60 5.1.5 Ozone 61 5.1.6 F-Gases and Halogenated Hydrocarbons (FC, CFC, HFC) 62 5.1.7 Sulphur Hexafluoride (SF6) 64 5.1.8 Indirect, Ozone-Forming Greenhouse Gases 64 5.1.8.1 Nitrogen Oxides (NOx) without Dinitrogen Oxide 64 5.1.8.2 Organic Compounds without Methane (NMVOC) 65 5.1.8.3 Carbon Monoxide (CO) 65 5.2 Sulphur Dioxide (SO2) 66 5.3. Aerosols 67 5.4 Changes in the Use of Land 72 6 Climate Observation 74 6.1 Temperature Trend near Ground Level 74 6.1.1 Average Global Temperature Trends 75 6.1.2 Warming Trends of the Land Surface Temperature from Satellite Data 76 6.1.3 The Past 420,000 Years - Climate History 77 6.1.4 The Past 10,000 Years - Climate History 78 6.1.5 The Past 1000 Years - The Hockey-Stick Discussion 78 6.1.6 Urban Heat Islands 81 6.2 Regional Climate Changes 82 4 6.2.1 Climate Trend in Asia 84 6.2.2 Climate Trend in Europe and Germany 85 6.3 Troposphere - Satellite Measurement 87 7 Climate Research Institutes and Programmes 91 7.1 IPCC 91 7.1.1 The IPCC Working Groups 92 7.1.2 Important Findings of the 3rd and 4th IPCC Report (TAR, AR4) 94 7.2 Research Programmes 96 8 Climate Models and Model Results 97 8.1 Climate Models 97 8.1.1 Coupled Atmospheric Circulation Models 99 8.1.2 Earth System Models 101 8.1.3 Uncertainties in the Climate Model Calculations 102 8.2 Results of Model Calculations 104 8.2.1 Emission Scenarios 104 8.2.2 Climate Projections for TAR (2001) - Model Results 106 8.2.3 Climate Projections for AR4 (2007) - Model Results 107 8.2.4 Regional Model Esulta 109 8.2.5 Detection of the Greenhouse Effect - Influencing Factors on Model Calculations 111 9 Impacts of Climate Change 115 9.1 Temperature Extremes 116 9.2 Precipitation, Floods 117 9.3 Storms and Hurricanes 118 9.3.1 Storms 118 9.3.2 Hurricanes (Tropical Cyclones) 120 9.4 Ice 123 9.4.1 Glaciers 123 9.4.2 Antarctica 125 9.4.3 Arctic 126 9.4.4 Greenland 129 9.5 Ocean 130 9.5.1 Warming and Acidification of the Seas 130 9.5.2 Sea Level Rise 131 9.6 Climate Impacts on Mankind, Nature and Environment 133 9.6.1 Damage – Statistics, Costs 134 9.6.2 Health 138 9.6.3 Benefits 140 9.7 "Hazardous Climate Change" 141 10 Emissions from Energy Conversion and Energy Transport 143 10.1 Emissions of Water Vapour, Waste Heat 144 10.2 Carbon Dioxide Emissions 145 10.3 Methane Emissions 150 10.4 Dinitrogen Oxide Emissions 151 10.5 Ozone Emissions 151 10.6 Nitrogen Oxide Emissions 151 10.7 Emissions of Volatile Organic Compounds without Methane (NMVOC) 152 10.8 Carbon Monoxide Emissions 153 10.9 Sulphur Hexafluoride Emissions 153 10.10 Sulphur Dioxide Emissions 153 10.11 Emissions of Fine Dust 154 5 11 Geoengineering and Reforestation 155 11.1 Fertilising with Iron in order to Increase Growth of Algae 155 11.2 Reforestation 156 11.3 Tillage 156 12 Carbon Dioxide Reductions in the Power industry 157 12.1 Efficiency Improvement 157 12.2 Renewable energies 159 12.3 Nuclear Energy 162 12.4 Emissions Trading 162 12.5 Carbon Dioxide Capture and Storage 165 12.5.1 CO2 Capture 166 12.5.2 Transport of Captured CO2 167 12.5.3 Storage 167 12.5.4 Conversion/Use of CO2 168 12.5.5 Cost Estimate 169 13 Resumée 171 14 Glossary 172 15 Abbreviations 183 16 Selected Literature 186 16.1 Books, Brochures 186 16.2 Articles (selection of literature, particularly after the IPCC Report 2001) 187 17 Internet Addresses 208 18 Annex – Statements about Climate Change 209

6 7 Preface On 2nd of February, 2007 the ‘Summary for Policymaker’ of the 4th Assessement Re- port (AR4), Working Group I (The Physical Scientific Basis), IPCC was published. The whole report will be published in the course of 2007. To that end, a first update of the literature research was performed. The findings of the literature research of October 2006 were confirmed in a wide range. The main statements and figures of AR4 were included and some new results from papers which were published since October 2006 and new statistical values for 2006, as far as available, were added, too. 10.03.2007 Preface For decades, the power industry has been concerning itself with the climate change, although the power industry is globally for 25 % of the greenhouse gas emission responsible and the German industry for about only 1 % of the world-wide carbon dioxide emissions. The carbon dioxide emissions which are inevitably connected to the combustion of fossil fuels, doubtlessly contribute to the anthropogenic greenhouse effect. In addition to the extent of their contribution to the greenhouse effect, its possible consequences are also of utmost importance.

The first time that the working group "CO2 and the climate" of the VDEW researched the literature about this topic was as early as at the end of the 1980s. Owing to the constantly growing scientific findings, in 1991 and in 1995 updates of this literature research were made. Yet, this topic has become ever more important, which on the one hand is due to the great amount of new findings, and on the other hand due to the Kyoto Protocol which entered into force in 2005. The power generating industry was faced with new challenges due to the political decisions concerning the establishment of reduction targets and the emissions trade meanwhile introduced at EU level. Therefore, a new update was urgently required. The present research is a completely revised edition which became necessary due to the large number of new findings. The objective of this study is a fundamental representation of the scientific contexts and the current level of the scientific climate discussion. The development of the global, national and local climate-relevant emissions, as well as the possibilities for reducing the carbon dioxide emissions caused by the power industry will also be dealt with extensively. On the basis of the 3rd IPCC report 2001 (TAR), many publications in scientific journals and reports of different institutes were analysed up to October 2006. Only those which are most important for this study appear in the literature list. In our times which are strongly influenced by the media, it is not always easy to see how far science has really advanced. Time and again, news concerning seemingly new scientific context create confusion, especially if they contradict the contexts that had been generally assumed so far, or if the new findings are modified only a short time after they had been presented. In the meantime, science itself is affected by the media hype, and each new bit of knowledge is published in press releases which often are exaggerated. It can be generally observed that in the last 25 years the climate scientists have detected a greater variability in the natural climate pattern of the past 1000 years, but that there is also an increase in the signs for an anthropogenic contribution to the climate changes that are taking place at present. This statement is also contained in the new 4th IPCC report (AR4). The annex lists an overview of the statements by scientific associations concerning the climate change. The power industry is affected by a climate change in manifold ways, not only because of the higher costs for a power generation with reduced or without CO2 emissions or by the costs for the emission certificates, but also by the repercussions of the climate change itself. Higher temperatures in winter reduce the number of heating days, but lead to an increase in the energy consumption in summer due to an extended operation of air conditioning systems. 8 Changes in the water level of rivers - low as well as high water - may influence the power generation of the hydroelectric power plants, or the shipping of fuels to the power plants. Also the networks operation can be affected. Temperatures that are too high cause problems due to the elongation of the lines, and the formation of ice, like in winter 2005/06, may lead to line breaks and power failures. An accumulation of stormy weather conditions does also lead to power failures because of, e.g., broken trees and tumbling pylons. The internet has developed into an excellent communications medium which allows the research of nearly all the published literature on the internet. Some international conferences may be heard live on the internet, or it is possible to read about them only a few days later. University teachers publish their lectures on the internet, and institutes publish directly their newest science findings on the internet. The IPCC – the Intergovernmental Panel on the Cli- mate Change - which plays an important role in the scientific discussion about the climate change also publishes its reports on the internet. Even the USA which have not signed the Kyoto Protocol but work intensively and with extensive financial funding on the research and clarification of the scientific contexts, publish the findings of their extensive national research programme in the internet, first for its evaluation and then, after having accepted proposals for correction, in a final version. Thanks to the intensive research in the field of climate change, the number of specialised publications has multiplied in the past years. Data concerning the greenhouse emissions, the atmospheric concentration of the trace gases, the changes in the climate, the variations of solar activity, and much more can be looked up directly on the internet on the pages of the relevant international organisations. The internet also offers some interesting discussion rooms about the climate problems. Even some climate scientists have founded such discussion rooms which quickly react to the newest findings, explain them and discuss them. The most important internet addresses are compiled in chapter 16. Because they are often a very descriptive illustration of the complicated scientific contexts, some of the illustrations used are taken from the climate pages of the Hamburg Educational Server (www.klimawissen.de), by kind permission of the author, Dr Dieter Kasang. Other illustrations are taken from the original studies published in the internet or from the internet pages of the institutes and organisations. The literature research was compiled by Dr.rer.nat. R. Beising (former EnBW) and was ac- companied by a project group (Dipl.-Met. A. Böhringer, EnBW, Dipl.-Met. Michael Wilhelm, RWE, Dr.rer.nat. Gerd-Rainer Weber, GVSt, Dipl.-Phys. Volker Hamacher, VGB). 9 Summary The literature research summarises the scientific foundations for the understanding of the climate changes, describes the natural and man-made factors of influence, the state of the art of the climate observations, the research programmes and the climate models with their most important results. After describing the repercussions of the climate change that have already set in or are prognosticated, the climate-relevant emissions and their contribution from the energy conversion are depicted. The general possibilities for reducing the carbon dioxide, like reforestation, and the special activities of the power industry (efficiency improvement, renewable energies, CO2 separation) are discussed at the end.

Scientific Foundations The climate is defined as the average value of the weather over a period of 30 years. Next to statistical parameters, like the average yearly temperatures and precipitation, also the probability and number of occurrences (average duration of droughts, frequency of storms, frequency of heavy precipitation,) play a role. The climate is influenced by the varying solar radiation, by volcanism, winds and ocean currents and their complex interaction with the pedosphere and biosphere. The climate system consists of five elements: the atmosphere, the hydrosphere (oceans and water circulation), the cryosphere (ice and snow), the biosphere (animals and plants) and the geosphere (soil and rock). The dispersion of the existing carbon on the earth over the individual parts of the system (e.g. the earth crust, oceans, plants, atmosphere), and the exchange of carbon between the systems is referred to as global carbon cycle. The most important energy source for the earth is the sun. At present, about 1367 W/m2 short-wave solar radiation reaches the troposphere. The energy assimilated within a thermal equilibrium is emitted back into space as thermal radiation. Various natural and anthropogenic factors influence the energy budget of the earth. The radiative forcing is a scale for the influence of a natural or anthropogenic factor on the change of the radiation budget of the atmosphere. The term "greenhouse effect" describes the processes in our atmosphere which - similar to a greenhouse - lead to the warming of the atmosphere. The augmentation of the concentration of the so-called greenhouse gases like water vapour, carbon dioxide, methane, dinitrogen monoxide, ozone and the synthetic chlorofluorocarbons in the atmosphere lead to an additional temperature rise. Climate changes can arise due to internal interactions within the climate system, but also external factors, like changes in the solar radiation, variations of the earth's orbit parameters and volcanic eruptions change our climate. The anthropogenic influences, like changes in the concentration of the greenhouse gases, aerosols, the ozone layer and the land use are counted as external factors. Another internal influencing factor is, among others, the extensive changes in the conditions of oscillations in the atmosphere.

Natural Influencing Factors on our Climate The sun has an essential influence on the climate of the earth. Only for about the past 30 years, has it been possible to measure directly via satellite the solar energy flux, including its variations. Changes in the solar energy flux are an important climate force. Changes in solar activity are reflected in the frequency of sunspots. They appear more often when the sun is more active. The solar activity which can be determined by the number of sunspots has not been as high as today for the past 8000 years. For the last 40 years, the analysis of the sunspots does not show any increase, which means that they do not explain the rising global temperatures since 1975. The solar wind influences the cosmic radiation and with it the formation of ions in the atmosphere which could promote the formation of clouds. Until today, it has not been possible to establish a link to climate changes. Explosive volcanic eruptions emit large quantities of solid material and gases into the atmosphere, partly even into the stratosphere. The aerosols lead to a change in the radiation balance and, in general, to a temperature increase of the stratosphere and a cooling down of the earth surface for 1 to 2 years. 10 The North Atlantic Oscillation (NAO) is one of the dominating oscillation patterns for the natural climate variability of the northern hemisphere. It strongly influences especially the winter weather in Europe and North East America. Stratospheric and anthropogenic processes can influence the phases and amplitudes of the NAO. The possible anthropogenic contribution to it has not yet been settled unambiguously. Together with the deep sea currents, the surface circulations of the oceans are part of a circulation system of all three oceans and form the so-called thermohaline circulation (THC). There is a discussion about the danger of a disruption of this "marine conveyor belt" which is so important for our climate. Recent model simulations show a differentiated behaviour in the case of a further temperature increase, and only a small danger of a disruption of the marine conveyor belt and, with this, the absence of the Gulf stream in the forthcoming decades. The strongest natural climate fluctuation for periods of some months up to several years is the El Niño/Southern Oscillation Phenomenum (ENSO). El Niño is characterised by an unusual increase of the ocean surface temperature along the equator from the Peruvian coast into the central Pacific. Notwithstanding extensive model calculations, scientists still discuss whether the global warming influences El Niño, or to the contrary, whether El Niño has consequences onto the global average temperature.

The most important natural greenhouse gases are water vapour, CO2, CH4, O3 and N2O, which due to their absorption behaviour in the atmosphere raise the global average temperature near the soil from -18 °C to about +15 °C.

Anthropogenic Influencing Factors The human being is part of the biosphere, and just by his mere existence he inevitably influences his environment, and with this the climate system.

The most important anthropogenic greenhouse gases are carbon dioxide (CO2) and methane (CH4), ozone (O3), dinitrogen monoxide (N2O), fluorocarbons (CFC, H-FC) and SF6. Their contribution to the anthropogenic greenhouse effect amounts to 4 % for N2O and 61 % for CO2. The models take into account the important role of the water vapour as a feedback mechanism.

Since the beginning of the industrialisation, the carbon dioxide (CO2) level has risen by about 35 %. The yearly increase in the concentration for the last two decades amounted to about 0.4 %. In 2006, the global medium concentration in the atmosphere rose by about 2.3 ppm up to 381 ppm. The carbon dioxide increase since the middle of the 19th century can be attributed to human activities. In the period from 1960 until 2005, the CO2 emissions have more than tripled reaching 27.3 billion t. Due to the yearly absorption of carbon dioxide by the biosphere and the ocean by about an average of 40 – 60 %; the concentration increase has clearly slowed down.

Methane (CH4) is the second most important greenhouse gas. Since the middle of the 18th century, its concentration in the atmosphere has risen by about 150 %. In the last 15 years, the increase rates have clearly diminished. On a world-wide level, about 500 million tons are emitted per year, to which man contributes about 60 – 70 %. The main anthropogenic share can be attributed to cattle raising (28 %) and the cultivation of rice (11 %), mining, oil and gas exploitation (24 %). Further shares are due to landfills and biomass combustion. Natural sources are marshlands, swamps (tundra) and the tropical rainforest, as well as termites, sea and methane hydrates.

Nitrous oxide (N2O) is a relatively stable and long-lived greenhouse gas which contributes directly to the greenhouse effect with about 4 %. Since 1750, the nitrous oxide concentration has increased by about 17 % and is still rising. N2O is emitted from natural (approx. 61 %) and anthropogenic sources (approx. 39 %). Above all, these are oceans, soils, the combustion of fossil fuels and biomass, the use of fertilisers and various industrial processes.

Ozone (O3) is a very climate-active greenhouse gas and is not directly emitted from natural or anthropogenic sources into the atmosphere. In the troposphere, ozone has detrimental effects on health, yet in the stratosphere, ozone absorbs the unhealthy UV-B radiation. Com- 11 pared to the pre-industrial value, the ozone concentration has increased by about at least 25 % near ground level. In contrast thereto, a significant decrease has taken place in the stratosphere. It is expected, that due to the prohibition of the ozone-destroying CFCs (Mont- real Protocol) the reduction of the ozone layer in the stratosphere will be stopped in the long term and that the ozone layer will recover by 2050. Despite their low concentration in the ppt range, fluor gases and halocarbons have different effects: The fluor gases (fluorocarbons, HFC) are "only" greenhouse gases and are a substitute for the halocarbons (especially CFC), which destroy the ozone layer in the stratosphere and contribute to the warming in the troposphere. This makes them the third most important greenhouse gas after CO2 and CH4. In addition to this warming effect, they also have an indirect cooling effect which is due to the depletion of the ozone layer in the stratosphere. The destruction of the ozone layer in the stratosphere leads to a clear cooling-off which also influences the troposphere. Since the beginning of the 1940s, and until the 1990s, an increase of the CFCs in the atmosphere was measured. Then, the increase of the completely halogenated CFCs started to drop or to slow down. The less critical substitution substances - partly halogenated CFCs with a reduced greenhouse potential - are still increasing, albeit at a slower rate. In Germany, the HFCs have increased. In contrast thereto, the CFC emissions have dropped.

Sulphur hexafluoride (SF6) is chemically extremely stable, the medium lifetime is several 1000 years. Additionally, it has a very high greenhouse potential and has practically no natural origin in the atmosphere. Among others, SF6 is used as a spark extinguishing gas in high- voltage switchboards, as tyre fillings, as isolating gas in thermal protection windows and in the aluminium production. Due to leakages, small amounts escape into the atmosphere. The SF6 concentrations in the atmosphere increase at about a few ppt per year.

Indirect, Ozone-Forming Greenhouse Gases

Nitrogen oxides (NOx, especially NO and NO2) are no greenhouse gases, but they destroy the OH radical, which influences the concentration of methane, carbon monoxide and CFCs in the atmosphere. Additionally, NOx contributes to the formation of ozone in the troposphere by photochemical processes. Sources for the NOx emissions are the combustion of fossil fuels and biomass, lightnings and soils. The combustion of fossil fuels causes about 60 % of the global NOx emissions. In the presence of nitrogen oxides and sunlight, volatile organic compounds (VOC) form the greenhouse gas ozone in the atmosphere. VOC are carbon compounds which are formed especially during an incomplete combustion process. They proceed from the motor vehicle traffic, industry, heating systems, chemical production processes (refineries, chemical plants) and escape during the evaporation of solvents. Natural sources emitting them in large quantities (2/3 of the global emissions) are deciduous and coniferous trees. Carbon monoxide (CO) is the most important indirect greenhouse gas, because it contributes to the formation of ozone in the troposphere. CO derives from natural as well as anthropogenic sources. On a global scale, the oxidation of methane and the combustion of biomass are important direct sources. The use of fossil fuels (traffic, industry, heating) - especially in the case of incomplete combustion - is in the northern hemisphere an equally important source. Since the 1950s until the middle of the 1980s, an increase of the atmospheric CO content of 0.3 up to 1 % per year was observed; later it came to a standstill.

Being the precursor substance for the sulphate aerosols, sulphur dioxide (SO2) is an important tropospheric trace gas. Since the sulphate aerosol belongs to the "dispersing aerosols", it counteracts the greenhouse effect and thus has a considerable effect on the development of the climate.

SO2 sources are above all the combustion of fossil and biomass fuels, volcanoes and the oxidation of dimethylsulphide (DMS) from the oceans. In the Northern hemisphere, SO2 is mainly emitted by power plants, industrial furnaces, domestic fuelling and traffic. In most of the industrialised countries, the immissions have dropped considerably. Due to the advanc- 12 ing industrialisation in the Asian threshold countries, significant increases have been found there. In the past years, aerosols have become increasingly more important in climate discussions. Aerosols are emitted into the atmosphere either directly (primary aerosols), or they originate from chemical processes from precursory substances (secondary aerosols). Aerosols are small particles which are floating in the air; they have a diameter of less than 10 µm and can reach the atmosphere due to natural processes like wind, volcanic eruptions or the combustion of fossil fuels or biomass. In principle, a difference is made between the direct and indirect influence of aerosols on the radiation budget and the climate. Aerosols (especially the sulphate particles) reflect the solar radiation into the space, and connected to it, they have a direct cooling effect. The indirect effect of the aerosols derives from their influence onto the cloud formation and precipitation. Additionally, they have also a semi-direct effect due to the disintegration of clouds as a consequence of the warming of the absorbing soot particles. Indications in the literature concerning the direct influence of aerosols vary greatly. It has been tried to determine the global climate effect by means of model calculations. Accord- ing to them, in the period between 1860 and 1985, the aerosols are said to have caused an average global cooling of about 0.9 °C. There are still a lot of uncertainties about these calculations.

Changes in the Use of Land Changes in the use of land are caused by deforestation, reforestation, irrigation and urbanisation. Nearly one third of the land surface is covered with forests. The most extensive deforestation is taking place in Africa, Asia and Central and South America with a loss ratio of more than 0.5 %/year. The exploitation of the soil changes the structure of the terrestrial surface, because agricultural surfaces are often brighter than forest areas, and they also show a different evaporative behaviour. On the global average, a slight cooling down will be probable, basically due to the increasing reflection of solar radiation. Model calculations which take into account the changes in the exploitation of the soil like deforestation and the extension of agriculture, establish considerable regional climate changes.

Climate Observation Since about 1850, the atmospheric pressure and the temperature have been measured for great parts of the earth surface. Since the beginning of the industrialisation in the middle of the 19th century, the average temperature of the earth rose by about 0.8 °C. The main increase occurred between 1910 until about 1945 and, after a slight decrease, since 1975 until today. 2005 was the second warmest year since 1861. Eleven of the last twelve years (1995 – 2006) rank among the 12 warmest years since 1850. The global average temperature increase of the past 50 years is attributed mostly to human activities. According to the IPCC 2001 and with more confidence to the IPCC 2007, the following indications point to it: there are nearly no changes of the natural influences like the solar and volcanic activity in this period; the spatial distribution of the temperature changes corresponds to the pattern as expected for the greenhouse effect, and the present warming is reconstructible (to a large extent) by the climate models only when considering the additional greenhouse effect. The evaluation of the data from ice cores of the last 650,000 years shows temperature variations of about 10 °C, which most probably were triggered by changes in the earth's orbit. Since the last Ice Age, the climate has been considered to be relatively stable with temperature variations of about ± 1 °C. The average temperature of the Ice Age was about 5-6 °C lower than our value today. The debated temperature diagram for the past 1000 years, which was published in the latest IPCC report and was reconstructed from historical data, shows the form of a hockey stick - a slight decrease of the temperatures until about 1900, then a steep rise until today. More recent evaluations show greater climate variability in the past centuries, especially a clear temperature rise in medieval times and a decrease during the little ice age. The so-called "urban heat island effect" is practically of no importance for the global development of the temperature. 13 Regional climate changes: The evaluation of regional and seasonal trend analyses draws a complex picture. Next to regions with temperature increases, there are also regions which have cooled down in the last 100 years. Since the 1980s, China has experienced a clear climate change - probably due to increasing soot and sulphate emissions and deforestation. The summerly rain belt has moved, and most of the summers were characterised by droughts. In total, the temperature increase between 1901 and 2003 is statistically significant, with 0.95 °C in Europe and with 0.8 °C in Germany. In the past two decades, there has been noticeable winter warming of 2.3 °C, compared to the summer with 0.7 °C. In the last century, and particularly in the last three decades, the winter precipitation has clearly increased. Satellite measurements: Since 1979, polar-orbit satellites have been observing the earth's atmosphere nearly completely. Whereas the troposphere has become warmer by 0.12 – 0.18 °C per decade since 1979, within the same period the stratosphere has cooled down by 0.32 – 0.44 °C per decade.

Research Institutes and Programmes The IPCC is an international expert panel of the UN with scientists of different disciplines, which documents the state of the art of the international climate research by means of the reports and publications of the three working groups. The first working group (WG I) deals with the scientific findings about climate-influencing factors. The second working group (WG 2) assesses the ecological and socio-economic effects of global warming, and the third working group (WG 3) analyses possible strategies for combating the greenhouse effect. The most important conclusions from the 3rd Assessment Report 2001 (TAR) were: There is a new and clear proof for the fact that the major part of the warming observed in the last 50 years must be attributed to human activities. Human influences will continue to change the atmospheric composition in the course of the 21st century. Based on the corresponding un- derlying scenario, an average global temperature rise of 1.4 °C up to 5.8 °C is projected for the period 1990 to 2100. Meanwhile, significant progress has been made in the preparation of the 4th Assessment Report (AR4), which is to be published in 2007. The Summary for Policymakers of the 4th Assessment Report (AR4) of Working Group I (The Physical Science Basis) presented 2nd February 2007 comes to even clearer findings than in 2001: Today, there cannot be well-founded doubts (‘very high confidence’) anymore that man has caused the global warming of the past decades. There is a growing amount of evidence for the fact that mankind influences further aspects of the climate, among others widespread melting of snow and ice, sea level rise, heat waves and other weather extremes, the air circulation, storm trails and precipitation. Since the beginning of the 1980s, many climate research programmes have been launched at world-wide level. Their aim is to determine to which extent it may be possible to predict natural climate fluctuations and the anthropogenic influence. To this end, research concentrates on a description of the current condition of the climate, the forming of models, the decisive climate processes and the future climate development.

Climate Models Climate models describe the climate system of the earth in physical-mathematical equations, which a computer can solve numerically. Coupled models (GCM) link the basic physical laws in the form of differential equations and calculate the most important atmospherical processes and variables of the condition for each grid point. From the results the weather statistic - which is the climate - is derived. A complete climate model contains the physical description of all the climate components and allows for their coupling. Despite all the uncertainties that still exist, it is meanwhile possible to reach quite a good agreement between the climate calculations from the model simulations (control runs) and the historically reconstructed climate. Model results: Major advances in climate modelling and the collection and analysis of data were reached since the last report TAR. According to the 4th Assessement Report of the 14 IPCC 2007 (AR4) the best estimates of the projected globally averaged surface warming for the end of the 21st century is for the low emission scenario (B1) likely 1,8°C (1,1°C to 2,9°C) and for the high emission scenario (A1F1) 4,0°C (2,4°C to 6,4°C). Despite the considerable progress made for the development of climate models, climate simulations have to tackle a large number of problems. As an example, it is difficult to correctly integrate the effect of clouds into the climate models. The manifold interactions of clouds have not yet been understood in detail. Clouds may have a cooling, but also warming effect.

Impacts of a Climate Change Statements about changes of global average values alone do not yet offer any indications about the impact a climate change could have on nature and mankind. Climate changes may cause positive as well as negative effects on man and nature in different regions. Pure statistical considerations lead to expect an increase in hot days if the mean temperature rises. Since more water evaporates, it is expected that the intensity of strong precipitation and floods will increase, too. The discussion among the scientists about a possible increase in the numbers of storms and hurricanes is still in progress and partly very controversial. Model calculations have shown that under future climate conditions extreme storm tides at the North Sea coast could increase. In the case of doubled carbon dioxide concentration, also low pressure activities over North Western Europe could increase. Changes in the hurricane activities are based primarily on natural variations, but the rise of the surface temperature of the oceans in the tropical zone could be a "contributory element" to the growing strength of hurricanes. Glaciers and ice caps bind considerable amounts of water which are equivalent to a sea level of about 70 m. For decades, the majority of the investigated glaciers have clearly ablated. The loss of the average mass balance has accelerated in the past years. Ablation had already started before industrialisation. While experts agree that the Antarctic ice sheet is relatively stable on the east side, they are not so sure about the behaviour of the Western Antarctic ice mantle. But they assume that in the case of a further temperature rise, the ablation of edges of the Western Antarctic and in Greenland could lead to a considerable sea level rise. Satellite data show that the sea ice layer in the Arctic has considerably shrunk by about 9 % in the last 25 years with larger decreases in summer. At the same time, the thickness of the sea ice layer has decreased by about 15 %. But the development of the sea ice and temperatures is characterised by ten-yearly variations, as evaluations of the last 100 years show. Next to natural causes like changes in the Arctic Oscillation (AO), also the greenhouse effect could play a role in the temperature rise over the last 3 decades. Model calculations lead us to expect a temperature rise of 3.5 °C up to nearly 6 °C by 2100 for the Arctic. These changes in the Arctic could have considerable consequences for the earth's climate. The ice cap of Greenland which is up to 3,000 m thick and 1.7 million km2 large, plays a special role in the climate discussion. Measurements of the ice and snow masses in Greenland have so far not yet shown a clear tendency, although the glacier ablations at the edges of Greenland have increased. But in the case of a continued temperature increase, most of the models show an ablation of the Greenland ice. Newer model calculations show that a global warming of 3 °C would have the Greenland ice cap rapidly melt. In the past 40 years, the oceans have warmed up due to the anthropogenic greenhouse effect. Observations have shown that 84 % of the total earth warming (oceans, atmosphere, continents, and cryosphere) of the past 40 years has been absorbed by the oceans. Due to thermal expansion, a temperature increase in the oceans inevitably leads to a sea level rise. According to satellite evaluations, the last years have proven an accelerating increase in the sea level which now amounts to 3.1 mm per year (1993 – 2003). Temperature increase, changes in precipitation and sea level rise can influence man and nature in most different ways: - Health (deaths due to extreme heat or cold, infections, communicable or other diseases) 15 - Agriculture (crop yield, irrigation) - Water resources (water stocks, water quality, and competition for water) - Coastlines (erosion of beaches, flooding of islands, coastal protection) - Flora and fauna (loss of species, changes in the habitat, glacier shrinkage) - Infrastructure (destructions due to storms and floods) - Tourism (less winter sports, more summer vacations e.g. at the North Sea and Baltic Sea) Statistics about natural disasters caused by the weather, and their damage to national economies, which are drawn up especially by the insurance industry have to be considered with caution. The increase in the amount of loss is not inevitably connected to an increase in storms, floods or precipitation. Often man himself has contributed to an increase in the amount of loss by settling in critical areas like coastal zones or at river banks. The assumed costs of the climate change in the 21st century vary in a wide range. In order to minimise the consequences of the climate change, there is a discussion about the adaptation at global level and also in Germany. Health: The WHO estimates that the anthropogenic influence on the temperature rise and increased precipitation has caused the death of about 150,000 people per year over the past 30 years. Yet, this statement is connected to a high degree of uncertainty. Next to death cases due to heat and nutritional deficiencies as well as floods, also death cases due to infections are considered. Thereby, Malaria and the Dengue fever play a prominent role. None of the model calculations about the increase in diseases considers the measures for an adaptation in the health care, the development of new therapies or changes in the human behaviour which could e.g. lead to a considerable drop of malaria hazards. In Central and Northern Europe and in the USA, particularly the climate-depending vector-borne diseases meningoencephalitis and Lyme borreliosis, both transmitted by ticks, play an important role. Milder winter temperatures may have led to a higher infection rate. Benefits: The discussion about possible consequences of the climate warming often tackles negative impacts only. Thereby, it is overlooked that some regions may even enjoy positive effects. A moderate temperature increase should have mostly positive consequences. An example is the more pronounced growth due to CO2 fertilisation. Higher temperatures also promote the growth of many plants, and accordingly, the vegetation period is prolonged. Cer- tain regions in Europe, Asia or Canada will benefit from it for the present. Yet, if the temperature rise is too strong, and/or water shortages occur, there will be losses in the crop yield. On the long term the greater majority of impacts are likely negative. In order to avoid a "dangerous climate change", according to science the global warming should be limited to maximum 2 °C. This is only possible by a global and preferably quick limitation of the greenhouse gases emissions. 16

Energy Conversion and Transport Energy conversion and, to a limited extent, energy transport inevitably generate climate- relevant gases. At a global level, the anthropogenic contribution to water vapour emissions and waste heat is negligible. The carbon dioxide emissions have almost constantly increased since the beginning of the industrialisation, among others primarily due to the combustion of fossil fuels. Since 1751, a total of about 300 billion t of carbon has been released into the atmosphere, half of it during the last 30 years. The world-wide combustion of solid and liquid fuels accounts for 76.8 % of the emissions, and the combustion of gas for 19.3 % (2002). The power generation has a global share of about 32 %. Today, the highest growth rates for carbon dioxide emissions are in Asia. Also Australia and USA still present increase rates of about 20 %. The EU15 emissions have nearly stabilised, in particular due to the heavy reductions in Germany and Great Britain. The new EU25 member states have contributed to the clear reduction of -5.6 % for the period between 1990 and 2004. In the past, the increase in cattle raising and the cultivation of rice have, like the exploitation of coal, landfills, gas supply and the combustion of biomass, led to an increase of the methane emissions. The power industry has a share of about 20 %. In Germany, the methane emissions were reduced by almost 50 % between 1990 and 2004. The share of power plants amounts to 0.25 % and therefore is negligible. The global N2O emissions from stationary combustion plants amount to about 7 % of the total emissions of the industrialised countries. In Germany, the share of power plants is 6 %. At a world-wide level, the NOx emissions remained more or less constant between 1990 and 2000. The clear reductions achieved in the industrialised countries were levelled out by the increases in Asia. In Germany, they decreased by about 45 % from 1990 to 2004. In 2004, the share of power plants still amounted to about 17 %. The combustion of fossil fuels has a global share of about 28 % in the emissions of volatile organic substances (NMVOC). In Germany, the NMVOC emissions were reduced by about 65 % between 1990 and 2004. The share of power plants amounts to 0.7 % and therefore is negligible. The carbon monoxide emissions clearly decreased in Europe (in Germany by about 66 % between 1990 and 2004), but strongly increased in Asia. With 3 %, the contribution of the power plants in Germany is quite low. Traffic is responsible for the main share in it, with about 52 %. In the year 2000, the world-wide SF6 emissions amounted to around 6,000 t. In Germany, it has been possible to achieve a clear reduction of about 50 % (2005) since 1995 for switchgears and transducers. Today, the most densely populated states of the earth, China and India, suffer from fine dust due to the combustion of biomass and coal without sufficient filtering installations. In Germany, the total dust emissions could be reduced by about 90 % in the period between 1990 and 2004. The power plants have only a share of around 6 % in the fine dust emissions and have reduced their emissions by 99 %.

Geo-engineering The concept of geoengineering describes proposals for intended changes of nature. Related to the anthropogenic climate change, it intends to reduce or avoid the influences of the anthropogenic greenhouse effect. Examples are the artificial introduction of sulphate aerosols into the stratosphere, or the installation of huge sunshades in the space. More realistic is the proposal to stimulate the growth of algae and with it the CO2 uptake of the oceans by fertilising the sea with iron dust. Reforestation can bind considerable amounts of carbon in the biomass of the forests. Special ways of tillage may increase the amounts of assimilated carbon dioxide or may prevent their emissions due to cultivation. The Kyoto Protocol permits the industrialised countries to reduce part of their carbon dioxide emissions by reforestation in developing countries.

Carbon Dioxide Reductions in the Power Industry

A broad portfolio of energy production technologies including fuel switching (coal/oil to gas), increased power plant efficiency, and increased use of renewable energy technologies (e.g., biomass, solar, wind, hydropower, geothermal, etc.) and nuclear power is currently available 17 to reduce greenhouse gas emissions. Additionally, there is an intensive research concerning the carbon capture. In the past 30 years, the efficiency of fossil-fired power plants has increased from 31 % to 36 % on a global average. If the efficiency of the power plants was increased by around 5 % world-wide, it would be possible to save around 1 billion tons of carbon dioxide. In 2004, within the EU25 around 15 % of the electricity was generated from renewable energies (especially hydropower). In particular in Germany the increase rates for windpower were high. Nuclear power plants generate around 17 % of the power demand world-wide, and 31 % of the demand in the EU25 from nuclear energy which is free of carbon dioxides. Within the implementation of the Kyoto Protocol, the emissions trade started in the European Union on 1 January 2005. Within the enlarged EU25, 11,428 energy generating and energy intensive plants are obliged to participate in the emission trade. The utility companies criticise its limitation to the EU and the reduction of competitiveness which results from it, as well as the fact that the present system covers less than 50 % of the total CO2 emissions of the EU25. Different worldwide research and development projects accelerate the progress of the carbon capture for its application. The three most important options for the carbon capture in power plants are: CO2 capture after the combustion, combustion with O2 instead of air (oxyfuel process) and the carbon capture before the combustion with IGCC (integrated gasification of coal). All three separation concepts have in common that they require extensive additional equipment with considerable efficiency losses of around 8 – 13 percentage points for the power generation. Different pilot and demonstration plants are being planned or under construction. After its capture, the CO2 is compressed and liquefied for transport and storage. A number of possibilities are being discussed for the storage of the captured CO2: storage in geological formations (aquifers, oil and gas fields, coal ledges), storage in the sea or in the form of carbonate. To a smaller extent, also its industrial conversion/use is being considered. Cost estimates for separation, transport and storage of the CO2 show considerable variations from 20 to 60 €/t of avoided carbon dioxide. 18 1 The Climate of the Earth The World Meteorological Organisation (WMO) defines the climate as the average value of the weather over a period of 30 years. Often, the period between 1961 and 1990 forms the basis. According to the newer definition of climate, it also contains the statistical behaviour of the atmosphere which is characteristic for a relatively big time scale. Next to the statistical parameters like the average yearly temperature and precipitation, also the probability and number of occurrences (average duration of droughts, frequency of storms, frequency of heavy precipitation, …) are specified. The climate is influenced by the varying solar radiation, by volcanism, winds and ocean currents and their complex interaction with the lithosphere and biosphere. The climate system consists of five elements: the atmosphere, the hydrosphere (oceans and water circulation), the cryosphere (ice and snow), the biosphere (animals and plants), the geosphere (soil and rock) (Fig. 1.1). These subsystems of the climate interact with each other by exchanging energy, impulses and substances and influence each other in their state of motions, their heat content and their composition of substances (climate noise).

Fig. 1.1: Schematic view of the major components of the climate system, their processes and interactions (http://www.clivar.ucar.edu/publications/other_pubs/clivar_transp/powerpoint_fig/ClimateSystem.gif)

1.1 Atmosphere The earth's atmosphere is the envelope of air around the earth. It consists of different layers (Fig. 1.2) from the ground up: the troposphere, the stratosphere, the mesosphere, the ther- mosphere and the exosphere. They vary in height depending on their geographical position and seasonal changes. The development of the temperature in the atmosphere is shown in Fig. 1.4. The lowest layer, the troposphere, is of special importance and responsible for the weather pattern - radiation balance, clouds, precipitation, the flux of air masses, transport and conversion of trace gases, aerosols and heat (Stocker 2004). It is limited by the tropopause the altitude of which varies from around 8 km (Polar Regions) to about 17 km (equator). 19

Fig. 1.2: The atmosphere of the earth as seen from space (NASA) (http://www.atmosphere.mpg.de/enid/ACCENTde)

The troposphere is warmed up by the solar radiation which is absorbed by the earth surface. The temperature depends on the weather, the surface condition and the seasons. With increasing altitude, the temperature decreases from about a global mean of +15 °C at ground level to -50 °C in 10 km altitude. In the stratosphere which extends up to around 50 km, temperatures rise again. It contains the ozone layer which surrounds the earth and absorbs the solar UV-B radiation. This leads to a warming up of the atmosphere from above. About 99 % of the air masses are contained in the troposphere and stratosphere. The air (Fig 1.3) is composed of nitrogen with 78.08 %, oxygen with 20.95 %, argon with 0.93 %, and carbon dioxide with 0.038 % (in dry condition). Surrounding air additionally contains humidity - up to 4 % of water vapour. The values fluctuate roughly between 0.1 % at the poles and 3 % in the tropics.

Gas, chem. formula Volume fraction Gas, chem. formula Volume fraction

Nitrogen, N2 78.08 % Dinitrogen monoxide, 0.3 ppm N2O

Oxygen, O2 20.95 % Xenon, Xe 0.09 ppm (90 ppb)

Argon, Ar 0.93 % Ozone, O3 15 – 50 ppb

Carbon dioxide, CO2 0.038 % (380 ppm) Nitrogen oxides, NOx 0.5 – 5 ppb

Neon, Ne 18.2 ppm Sulphur dioxide, SO2 0.2 – 4 ppb

Helium, He 5.2 ppm Ammonia, NH3 0.1 – 5 ppb

Methane, CH4 1.8 ppm CFC-12, CF2Cl2 ~ 0.5 ppb

Krypton, Kr 1.1 ppm CFC-11, CFCl3 ~0.3 ppb

Hydrogen, H2 0.5 ppm CFC-22, CHCIF2 ~0.1 ppb

Fig. 1.3: Composition of dry (without water vapour) and pure (without aerosols) air near ground level (according to Schön- wiese 2003) 20

Fig. 1.4: The layers of the atmosphere with the temperature distribution (red) (Kasang, HBS 2005)

The forcing of the atmospheric movements is the solar radiation which varies in terms of time and regions. It creates differences in the temperature and, with this, in the density. They lead to air pressure differences which, next to gravity and frictional forces, are the most important forces which have effects on the air particles and move the air masses (Lemke, 2003).

1.2 Hydrosphere The hydrosphere contains all forms of water above and below the earth surface. This includes also the complete ocean and the global water circulation after the precipitation has reached the earth. It is responsible for the flow of water masses, the transport of heat and trace substances in the ocean, and for the exchange of water vapour and trace substances (also carbon dioxide). About 70 % of the earth surface is covered by oceans. The oceans have a mean depth of 4,000 m and contain 97 % of the total amount of water on the earth. Ocean and atmosphere play an important role for the interaction in the climate system. The influence of the warm Gulf Stream onto the temperatures in Central Europe is well known. The sea is the biggest thermal storage on earth. Due to the huge heat capacity and density, the top 3 m thick ocean layer contains the same amount of heat as the total atmosphere. Oceans damp the thermal fluctuations. Above the seas, the yearly and daily temperature changes are much less pronounced than above land. The influences are reciprocal: Wind causes waves and drives the ocean currents near the surface. There are many different ocean/atmosphere interactions which influence the climate 21 in many parts of the world. Ocean currents develop from wind effects or from changes in the density of the surface water as a consequence of the exchange of heat and fresh water. The biggest part of the solar energy which reaches the earth surface is consumed again by the water evaporation. This flux of "latent" energy is the most important energy source of the atmosphere. After having condensed into the troposphere, the water drops and ice crystals form clouds which again are of considerable influence onto the climate (Raschke 2002). The mean terrestrial coverage grade of clouds amounts to around 50 %. Some of the ocean/atmosphere interactions are the regularly recurrent El Niño Phenomenon in the tropical Pacific with water warming of up to 5 °C off the South American coasts, and occasional climate fluctuations in America, Asia and Europe. Also the monsoon rains in India and Africa are, among other things, probably linked to changes of the temperature of the ocean surface. Also in the case of the North Atlantic Oscillation (NAO) there is a discussion about the influence of surface temperatures. 1.3 Cryosphere The cryosphere includes any forms of ice in the climate system, which is land ice sheets, ice shelves, sea ice, glaciers and permafrost. It is a long-term water reservoir and influences the radiation balance of the terrestrial surface, as well as the salinity in critical regions of the earth. Ice covers about 10 % of the land surface and around 7 % of the sea, with the main part of ice covering the Antarctic continent. Glaciers have only a very small share in the terrestrial ice surface. An ice sheet insulates the soil like the water from the cold atmosphere, it stops the heat exchange and reduces the evaporation. Ice and snow play an important role in the transport of water and heat, as well as in the terrestrial radiation budget. Ice and snow reflect (albedo) up to 90 % of the solar radiation, but water and soil only 10- 20 %. A sheet of ice and snow increases the cooling of the soil, water and lower air layers. Additionally, sea ice is part of the forcing of the oceanic deep-sea circulation. Continental ice sheets are formed by compressed snow at constantly low temperatures. Over a longer period of time glaciers appear. Shelf ice floats on the sea where the continental ice sheet moves over the edges of the continents. It moves into the sea for some kilometres. Ice lumps that tear off form icebergs. At lower temperatures, the surface water of the oceans freezes to become sea ice. During the freezing process, the salt remains in the non-frozen water. Sea ice floats on the water surface and, due to tides and waves, breaks into individual ice floes. The ice floes are between 1 and 3 m thick.

1.4 Geosphere The soil is the limiting surface between atmosphere and biosphere and is of special importance for the carbon dioxide circulation. The soil contains around double the average amount of carbon dioxide than the plants above ground. The position of the continents has a decisive influence onto the climate zones and ocean currents. A change of the sea level, the ice formation, the conversion of short wave radiation into long wave radiation, the reflectivity (albedo) of the continental surface influence the climate, too. In particular over longer periods of time, the solid rock sheet below the soil (lithosphere) plays a role for the climate due to the weathering of rock and new formations by sea sedimentation, and over short periods of time due to volcanic activities.

1.5 Biosphere The biosphere is a global ecosystem driven nearly exclusively by solar energy. It consists of living organisms and that part of inanimate material which interacts with the organisms. It is characterised by complex, global substance circulations (Claussen 2003). The humans with 22 their economic activities are living beings and as such also part of the biosphere. By its functions, the biosphere is closely connected to the atmosphere, pedosphere and hydrosphere. The biosphere comprises the organic coverage of the continents (vegetation, soil) and the marine organisms. The biosphere determines the carbon dioxide exchange between the different reservoirs and, with this, the concentration of carbon dioxide in the atmosphere. The coverage of the soil by plants like trees, grasses and lichen has another direct influence on the climate because it is jointly responsible for the wind conditions, the albedo (see Fig. 1.5) and the evaporation. According to Raschke 2002, the average yearly albedo of the earth amounts to around 30 %.

Surface Albedo in %

Settlements 15 – 20

Tropical rainforest 10 – 12

Deciduous forest 15 – 12

Cultivated areas 15 – 30

Green land 12 – 30

Tillable ground 15 – 30

Sandy ground 15 – 40

Sand of dunes 30 – 60

Ice from glaciers 30 – 75

Fig. 1.5: Albedo of different continental surfaces. The albedo is the share of solar radiation that is reflected by the surface. (Source: Höper 1998, from Lfu Bayern 2004 (www.bayern.de/lfu/umwberat/data/klima/treibhaus_2004.pdf)) 23 2 The Carbon Dioxide Cycle Carbon dioxide is emitted into the atmosphere by the respiration of man and animals, as well as during the microbial decomposition of plants and the combustion of fuels which contain carbon dioxide (coal, wood, natural gas, oil). The CO2 in the atmosphere interacts with the ocean water and the plants of the landmasses. The dispersion of the carbon existing on earth over the individual parts of the system (e.g. the earth crust, oceans, plants, atmosphere), and the exchange of carbon between these systems is referred to as global carbon cycle. Fig. 2.1 shows this global carbon dioxide cycle. In the following, reference is made to the essential components and interactions of the global carbon dioxide cycle. On earth, carbon dioxide is stored in many reservoirs: in the atmosphere, in the water and oceans, in solid rocks like limestone, in fossil fuels like coal, oil and gas, in living plants and dead organic material like wood, in plant residues and humus in the soil. In addition to the atmosphere, the ocean and continental biosphere are the most important carbon reservoirs, which are actively interlinked with each other (Fig. 2.1). The atmospherical CO2 is relatively quickly exchanged with the ocean and the continental ecosystem. McNeil 2003 estimates the net absorbency of the oceans to be 1.6 to 2.0 ± 0.4 Gt C per year. Ac- cording to Hicke 2004 and Goodale 2002, the forests of the Northern hemisphere are an important carbon reducing factor and absorbed 0.6-0.7 Gt C per year during the early 1990s. In contrast to this, the tropical deforestation leads to a rise of carbon dioxide of about 0.6-0.9 Gt C/year (de Fries 2005). These figures are still subject to great uncertainties. The exchange of carbon dioxide between the oceans and the atmosphere is about 50 % higher than that between the atmosphere and the continental ecosystems. At present, the sea absorbs more of the anthropogenically emitted carbon from the atmosphere than the land. In the 1980s, this ratio was even bigger, yet it may be reversed by the so-called fertil- iser effect.

Fig. 2.1: The global carbon (dioxide) cycle for the 1990s, showing main annual fluxes in GtC yr-1: preindustrial ‘natural’ fluxes in black and ‘anthropogenic’ fluxes in red. Modified from Samiento and Gruber 2002, with changes in pool- sizes from Sabine 2004: flux of -140 GtC from the ‘Vegetation, Soil and detritus’ compartment represents the cumu- lative emissions from land use change. The net terrestrial loss of -39 GtC inferred from ocean storage requires a terrestrial biosphere sink of 101 GtC. (IPCC 2007)

For the development of climate models, it is of decisive importance to include the carbon circulation in the climate models (Heimann 2004). Friedlingstein 2006 reports that the coupling 24 of climate and carbon circulation was researched by means of 11 coupled climate/carbon models. All models show for the period until the end of the 21st century an increasing remaining part of carbon dioxide in the atmosphere, which means that land and sea will then be capable of absorbing less CO2.

2.1 Geosphere With 99.8 %, the earth crust is by far the biggest carbon reservoir. It absorbs carbon dioxide mainly from the biosphere (decaying plants) and from the oceans (due to sedimentation on the sea bed). The carbon is retained particularly in limestone containing carbonate and in sediments containing carbon hydrates (oil, bitumen, coal, cerogenes). The increase of carbon due to withering biomass is counterbalanced by a decrease which is bigger by an order of magnitude due to the exploitation of fossil fuels by man. Permafrost soil located at higher latitudes contains about 400 Gt C. A global temperature rise of 2° C could release 25 % of the carbon as CO2.

2.2 Ocean The complete amount of carbon dioxide absorbed in the sea is 50 times bigger than the atmospherical CO2 content. The gas exchange occurs predominantly in the 50 to 100 m thick oceanic top layer and is mainly driven by the difference of the partial CO2 pressure and the atmosphere. Due to the atmospherical disturbance of the carbon dioxide content, the sea absorbs at present around 1.7 Gt of C more per year than emitted (carbon sinks). According to the evaluation of 940,000 measurements of CO2 partial pressure, Takahashi 2002 finds higher values of about 2.2 Gt C/year (error around 20 %). The biggest CO2 absorption occurs between the 40th and 60th degree of latitude. In the past 200 years, the sea has absorbed about 120 billion tons of anthropogenic CO2 and, in doing so, has "relieved" the atmosphere by an increase in the concentration of 55 ppm (Sabine 2004). The total yearly carbon dioxide exchange amounts to approx. 100 Gt (Fig 2.2).

Fig. 2.2: The oceanic carbon circulation. Physical and chemical processes are marked in red, biological processes in green (DIC = dissolved inorganic carbon, DOC = dissolved organic carbon, POC = particles of organic carbon (tissue particles), lysocline = limit of carbonate saturation, thermocline = transition zone between warm superficial water and cold water of medium depths, detritus = biological trash (according to IPCC 2001, taken from Kasang, HBS 2005)) 25

The capability of CO2 absorption in the sea depends on the temperature. Due to the then reduced gas absorbing capability, a temperature rise of 1 °C leads to gas emissions and, consequently, to an increase of the carbon dioxide in the atmosphere of around 4 Gt C, which is around twice as much as the present yearly total absorption of anthropogenic CO2. In contrast thereto, cold regions enhance the CO2 absorption of the ocean. According to Waugh 2006, there are still many uncertainties about the CO2 absorption and its regional distribution, particularly in deeper layers.

Dissolved organic carbon in the ocean is mainly present as hydrocarbonate (HCO3-), because dissolved CO2 from the air reacts with water and carbonate to hydrocarbonate. If the CO2 content continues to increase, less carbonate will be present for the chemical reaction with carbon dioxide in the oceans in the future. Consequently, the capability of the oceans to absorb further CO2 from the atmosphere will drop in a longer term. According to IPCC 2001 this effect is relatively pronounced: In the case of a further increase of around 100 ppm (from 370 to 470 ppm), the CO2 absorption by the ocean will decrease by 40 %, compared to the first 100 ppm increase since the beginning of the industrialisation. CO2 is not only chemically converted but also absorbed by phytoplankton in the course of photosynthesis. Via ingestion by the zooplankton, it finally becomes waste and sinks to the sea ground as detritus.

Below the oceanic top layer, the CO2 content clearly increases, which is partly due to the fact that sinking water masses transport CO2 into the depths (physical pump), and partly due to sinking organic carbonaceous material (biological pump). Due to the thermohaline circulation, the big water masses which sink into the deep, effectively withdraw the CO2 from the exchange with the atmosphere for very long periods which often last for up to a thousand years, the circulation time of the ocean. Due to the warming of the ocean, less cold water masses are formed and sink down, which reduces the physical pump. The so-called biological pump is very effective and absorbs around 11 Gt C per year. Without the oceanic phytoplankton, the atmospherical CO2 concentration would be higher by around 150 to 200 ppm. This is why the increase of the nutrients content in the ocean is considered, in order to enhance the formation of phytoplankton (see chapter 11.1). The acidification of the oceans due to a higher CO2 content is also considered to be a growing problem (Feely 2004). All in all it is expected that the carbon sink strength of the ocean (among other things due to higher temperatures of the ocean water and the acidification) will probably decrease in the future, and with it a greater part of CO2 will remain in the atmosphere (IPCC 2001/2007, Sa- bine 2004).

2.3 Atmosphere The atmosphere contains around 0.001 % of the total amount of global carbon, mainly as carbon dioxide. Here, the CO2 is exchanged with the biosphere, the lithosphere (volcanoes) and the sea. The concentration increase of CO2 in the atmosphere by around one third from about 280 ppm in 1860 to approx. 380 ppm in 2005 must be attributed particularly to human activities.

2.4 Biosphere

The exchange of CO2 between the atmosphere and the biosphere occurs mainly via the photosynthesis of the plants during which carbon is stored. The respiration and decaying of plants, and the respiration of animals and humans release CO2 back into the atmosphere. Per year, mankind (around 6.5 billion) exhales about 0.6 Gt of carbon in the form of CO2, which beforehand was withdrawn from the atmosphere by the nutritional chain. The carbon of withered plants forms a carbon reservoir which partly is washed into the oceans by the rivers, and partly is stored in the soil (e.g. in the form of humus). All in all, per year around 150 Gt of carbon are transformed. Deforestation and the intensified agriculture lead to a quicker carbon dioxide transformation, although the amount of carbon stored in forests and in the soil is bigger than that in the remaining biomass. 26 Considerable uncertainties exist concerning the knowledge about the interactions of the atmospherical CO2 with the biosphere. These uncertainties concern the estimates and measuring inaccuracies for the indications about the conversion of forests into agricultural areas, the historical deforestations, the present carbon reserves and the deforestation rates in tropical regions. Also unsettled is the question whether the biosphere will convert from a sink into a source (Cox 2004) and thus might enhance the greenhouse effect (Scheffer 2006), and if so, under which conditions and starting with which CO2 concentration. Next to carbon dioxide also carbon monoxide and methane participate in the carbon circulation, but they play a minor role. 27 3 The Radiation Budget and the Greenhouse Effect The most important energy source for the earth is the sun. At present, about 1367 W/m2 of short-wave solar radiation reach the troposphere. The energy assimilated within a thermal equilibrium is emitted back into space as thermal radiation. Various natural and anthropogenic factors influence the energy budget of the earth.

3.1 Radiation Balance The radiation balance is the difference between the incoming global radiation and the radiation which is reflected or converted, respectively, by the terrestrial surface. For the climate system Earth, the long-term balance between incoming solar and thermal radiation reflected into space is decisive. The radiation processes lead to the global and yearly average radiation balance as shown in figure 3.1. The radiation balance indicates how much radiation (in which wavelengths) hits the terrestrial surface or leaves the earth.

Fig. 3.1: Global and yearly average radiation balance of the earth in W/m2. On the left side, the short wave flux is shown, on the right side the long-wave flux. The flux of latent and sensitive heat which results from the energy difference between the terrestrial surface and the atmosphere are shown in the middle (Kiehl and Trenberth 1997, IPCC 2007))

According to it, of the 342 W/m2 of incoming solar energy (equivalent to a total solar irradiance at the Earth of 1367 W/m2 averaged over the globe (1/4), see chapter 4.1.1) around 198 W/m2 reach the ground, of which 30 W/m2 are reflected again into space. The rest is either absorbed (67 W/m²) by the components of the atmosphere (gases, aerosols, clouds) or re-dispersed back into space (77 W/m2). Accordingly, of the incoming solar radiation around 31 % are reflected back to space, nearly 20 % remain in the atmosphere and 49 % are retained in the ground causing its warming. In order to equalise the radiation energy balance of the earth, the heat radiation of the planet into space needs to be a mere 235 W/m2. With 195 W/m2, the atmospherical gases, clouds and aerosols contribute to this, whereas around 40 W/m2 reach space directly from the ground via the atmospherical transmission windows. At ground level, another 324 W/m2 are added to the solar radiation flux. The high insolation of totally 492 W/m2 is dissipated from the terrestrial surface by a thermal radiation of 390 W/m2, convection of 24 W/m2 and evaporation of 78 W/m2 (Bakan and Raschke 2002). The reliable measurement of the radiative forcing turns out to be extremely difficult. Even satellite-based measurements did not offer unequivocal results yet. According to Wielicki 2005, the evaluation of satellite-based measurements showed that the terrestrial radiation dropped around one half percent in the years between 2000 and 2004. In 2005, Raschke re- 28 calculated the terrestrial radiative budget with many measured values from satellites and the ground. Compared to earlier examinations, big differences were found. The global mean values of energy insolation and reflection differ by up to 30 W/m2, so that new examinations will be necessary.

3.2 Radiative Forcing The radiative forcing (RF) is a scale for the influence of a natural or anthropogenic factor on the change of the radiation budget of the atmosphere. Radiative forcing is defined as the difference between the incoming radiation energy and the outgoing radiation energy in a given climate system. It indicates changes in the net radiation flux density from solar insolation and terrestrial reflection into the tropopause in Watt per square metre (W/m2). The increase of greenhouse gases in the atmosphere leads to a change in the radiative equilibrium and with this to climate changes.

Fig. 3.2: Global mean radiative forcing in W/m2 for greenhouse gases, aerosols and solar radiation, planes, land use with an estimate of the uncertainties (vertical green line) (1750-2000). As far as aerosols, clouds, the land use and the solar influence are concerned, the level of scientific understanding still is quite low (source: HBS Kasang 2005 according to IPCC 2001)

The columns in Fig. 3.2 show the global mean radiative forcing according to IPCC 2001 for the anthropogenic greenhouse gases, aerosols and the changes in the solar radiation and land use. The radiative forcings show the share for the period between 1750 and 2000. The lines indicate the quantitative uncertainties which are considerable in particular for the aerosols. With 2.45 W/m2, the long-living and well mixed greenhouse gases like carbon dioxide, methane, dinitrogen oxide and the CFCs have the biggest share in it since the beginning of the industrialisation. But also natural factors like the solar radiation, volcanic eruptions and mineral dusts are of considerable influence. In contrast thereto, the increased aerosols partly lead to compensated forcings, due to absorption and reflection (direct aerosol effect) and the changed properties of clouds (indirect aerosol effect) which are linked to it. The understanding of anthropogenic warming and cooling influences on climate has improved since TAR, leading to a very high confidence that the globally averaged net effect of 29 human activities since 1750 has been one of warming, with a radiative forcing of +1.6 (+0.6 to +2.4) W/m2 (Fig. 3.3).

Fig. 3.3: Global-average radiative-forcing (RF) estimates and ranges in 2005 for anthropogenic carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and other important agents and mechanisms, together with the geographical extent (spatial scale) of the forcing and the assessed level of scientific understanding (LOSU). The net anthropogenic radiative forcing and its range are also shown (IPCC 2007).

The combined radiative forcing due to increases in carbon dioxide, methane, and nitrous oxide is +2.30 (+2.07 to 2.53) W/m2. The carbon dioxide radiative forcing increased by 20% from 1995 to 2005. The anthropogenic contributions to aerosols together produce a cooling effect, with a total radiative forcing of -0.5 (-0.9 to -0.1) W/m2 and an indirect cloud albedo forcing of -0.7 (-1.8 to -0.3) W/m2. The aerosol forcings are now better understood than at the time of the TAR but remain the dominant uncertainty in radiative forcing. Ozone and halocarbons changes contribute to 0.69 W/m2 and changes in surface albedo, due to land-cover changes and deposition of black carbon aerosols on snow, exert respective forcings of -0.2 W/m2 and +0.1 W/m2. Changes in solar irradiance since 1750 are estimated to cause a radiative forcing of 0.12 (+0.06 to +0.30) W/m2, which is less than half the estimate given in the TAR (SPM, IPCC 2007).

3.3 The Greenhouse Effect The term "greenhouse effect" describes the processes in our atmosphere which - similar to a greenhouse - lead to the warming of the atmosphere. The so-called greenhouse gases like water vapour, carbon dioxide, methane, nitrous oxide (laughing gas), ozone and the synthetic chlorofluorocarbons have the special property to let the solar short-wave radiation pass nearly unhindered, but to absorb the long-wave reflection of the earth. This dissimilar permeability of the atmosphere for radiations of different wavelengths leads to the so-called greenhouse effect (Fig. 3.4). The greenhouse gases in the atmosphere absorb the thermal radiation (IR) emitted by the terrestrial surface and radiate themselves into space and onto the earth surface. The latter is reabsorbed by the terrestrial 30 surface, so that the atmosphere becomes warmer than without greenhouse gases. Before the beginning of the industrialisation, the natural greenhouse effect due to the concentration of these gases led to a warming of the earth by around 33 °C, from -18° C to +15° C. The absorption of the long-wave heat radiation of the terrestrial surface within the infrared spectrum occurs in differing absorption bands, depending on the greenhouse gas, in the so-called water vapour windows where the water vapour absorbs only partly (Bakan and Raschke 2002, Fig. 3.5).

Fig. 3.4: The energy balance of the atmosphere: black lines denote short-wave radiation; red lines denote long-wave radiation. Dotted lines demonstrate the vertical heat transport by evaporation and condensation (latent heat) and upris- ing warm air masses (sensible heat); values in W/m2. (Kasang, HBS 2005).

There is no linear relationship between the concentration of greenhouse gases and the greenhouse effect, because most of the absorption bands of the natural greenhouse gases are nearly saturated (Fig. 3.5). Therefore, only the marginal ranges of the absorption bands of natural greenhouse gases (water vapour, carbon dioxide, ozone) and the still unsaturated absorption bands of some greenhouse gases like the CFCs contribute to it (Claussen 2003).

Fig. 3.5: (a) Spectrum of the terrestrial (255 K) (as an idealised black body) heat radiation (red), the actual radiation (blue surface) due to the greenhouse gas effect, plotted above onto the log. wavelength scale of 0.1 until 60 µm. The product of wavelength and radiance on the ordinate guarantees that similar surfaces correspond to similar energy amounts (b) Wave ranges, in which the greenhouse gases absorb the heat radiation. The absorption coefficient (ordinate) is an indicator for the absorption intensity. The trace gases water vapour, carbon dioxide, ozone, nitrous oxide and methane are the most important natural greenhouse gases (according to IPCC 2001, Kasang HBS and Raschke 2002)

Due to the radiation of the energy previously absorbed by the greenhouse gases, the amount of energy which reaches the terrestrial surface increases. As on a long-term basis the radiation budget of the earth must be balanced, the energy quantity reflected by the earth will increase and, according to the Stefan - Boltzmann Law, also the terrestrial mean temperature. This law states that the emitted energy per unit area is proportional to the fourth power of the absolute temperature T (Fig. 3.6). The proportional constant which helps determining the power is called Boltzmann Constant.

Fig. 3.6: The theoretical temperature of the terrestrial surface is calculated with the Stefan-Boltzmann Law.

The energy balance is not only balanced by the radiation fluxes but also by the latent and sensible heat fluxes between the terrestrial surface and the atmosphere (Fig. 3.4). 32 In order to be able to compare the effect of the greenhouse gases, the so-called global warming potential, GWP, was introduced. It indicates how many more times a greenhouse gas contributes to the greenhouse effect than CO2, the global warming potential of which was defined to be 1 (with a mean residence time of 100 years). Methane has a GWP which is 23 times stronger than CO2, N2O 296 times stronger, and the CFCs up to 12,000 times. With 22,000, SF6 has the highest GWP. It allows comparing the different contributions of individual greenhouse gases to the greenhouse effect and converting the values into CO2 equivalents. This simplifies also the data entry for model calculations. Nevertheless, it must be taken into account that due to the uncertainties concerning the life span data and the indirect effect, the error range with ± 35 % is quite large (IPCC 2001).

F ig. 3.7: The relative molecular global warming potential, compared to the global warming potential of CO2 (=1) for a period of 20, 100, 500 years (in the case of methane, the indirect effect is included via the formation of ozone and stratospheric water vapour) (IPCC 2001)

Meanwhile, both from satellites and from the earth, alterations in the radiation have been measured which are due to the greenhouse effect. With the help of satellite measurements, Harries 2001 has measured the distribution of the heat radiation as a function of the wavelength in the range of the absorption bands of the greenhouse gases and has found a reduction of the heat radiation which was measured with different satellites in 1970 and 1997. Philipona 2004, of the World Radiation Center, Davos, has confirmed these findings by measuring the incoming infrared radiation at 11 measuring points in the Alps. As measurements have shown (Philipona 2005), in Europe the temperature rise of the last years was mainly caused by the increased water vapour content which is due to the greenhouse effect. 33 4 Natural Influencing Factors on the Climate Climate changes may be caused by internal interactions within the climate system, which at least in its subsystems behaves chaotically (Claussen 2003). But also external factors, like changes of solar radiation, alterations of the earth's orbit parameters and explosive volcanic eruptions, change our climate. The anthropogenic influences due to changes in the greenhouse gas concentrations, aerosols, the ozone layer and the land use (see chapter 5) are counted among the external factors. The internal influencing factors are, among other things, alterations of the oscillation conditions in the atmosphere (North Atlantic Oscillation (NAO), Arctic Oscillation (AO), air vortexes in the polar regions (Vortex), and the Southern Oscilla- tion (SO)), which is coupled to alterations of the ocean currents (El Niño Southern Oscillation (ENSO), and the Thermohaline Oscillation (THC). It is discussed how much these are influenced by human activities.

4.1 The Sun The sun has a mean distance of 149 billion kilometres from us. Inside the sun, nuclear reactions take place by the fusing of hydrogen atomic nuclei with helium atomic nuclei, which release enormous amounts of energy. This energy is moved to the surface (temperatures around 6,000°C) by convection and is emitted into the environment in the form of light and heat (Fig. 4.1).

Fig. 4.1: Eruption of prominences (glowing gas clouds) from the solar surface which may project up to 1 million km into the solar atmosphere (the earth is shown for comparison) (http://soho.esac.esa.int/)

The sun has an essential influence on the climate of the earth. In particular since starting satellite measurements in 1979, knowledge about the significance of the solar radiation as a climate factor has increased (Rind 2002, Cubasch 2002). Not only are the distance of the sun and the earth’s inclination within its orbit around the sun of importance (Fig. 4.2). Also the radiation itself has varied over years and millenniums. The solar radiation delivers more than 99.9 % of all the energy available for the earth/atmosphere system. The earth "wobbles" like a top which is falling over. Due to the precession, the earth's axis has inclined to the other side after around 11,000 years. One complete rotation takes 22,000 years. Owing to this "precession", the solar insolation on the Northern hemisphere varies accordingly. Additional periodical changes in the inclination of the earth's axis 34 (obliquity) and in the form of its orbit (eccentricity) lead to cycles with durations of 41,000 and 100,000 years. The larger the inclination angle, the bigger are the seasonal temperature differences. The superposition of these three parameters results in a pattern which correlates quite well with the ice ages (Milankovitch theory).

Fig. 4.2: Schematic of the Earth’s orbital changes (Milankovich cycles) that drive the ice age cycles. “T” denotes changes in the tilt (or obliquity) of the Earth axis, “E” denotes changes in the eccentrity of the orbit, and “P” denotes precession, i.e. changes in the direction of the axis tilt at a given point of the orbit. The earth's deviations from the orbit around the sun lead to periodical changes of the solar insolation on the earth which determine the terrestrial cold - heat periods (IPCC 2007)

4.1.1 Solar Radiation The question of how much solar energy is available on the earth depends on the solar radiation intensity and the orbit parameters of the earth (distance to the sun, axis inclination, rotational speed of the earth etc., see Fig. 4.3). The composition of the atmosphere (concentration of the greenhouse gases), the coverage by clouds and the terrestrial surface texture (e.g. forests, fields, glaciers, water) influence the amount of energy disposable at the terrestrial surface and reflected back into space. On a long-term basis, the solar luminous intensity, and with it the solar energy flux, change for nearly all time scales. In the course of her life, the sun becomes increasingly hot, and the solar energy flux which reaches the earth constantly increases in the course of millions of years (10 % / billion years). In order to understand the climate dynamics of the past several thousand years, the solar alterations of around 11, 22, 78, 211 and most certainly also 1,500 and 2,500 years are of importance (Claussen 2003). The most important cycle is supposed to be the very regular, nearly eleven-year so-called Schwabe cycle which alternates between 9 and 14 years.

Fig. 4.3: The intensity of solar radiation depends on the terrestrial orbit parameters (and on the properties of the atmosphere and terrestrial surface which determine absorption and reflection (Kromp-Kolb Wien) (http://www.iff.ac.at/socec/backdoor/sose05-ring-sozoek/11_KrompKolb_WKOKlima.pdf)

Only for about the past 30 years, has it been possible to directly measure via satellite the solar energy flux, including its variations (fig. 4.4). The mean value of the solar insolation (= solar constant) was found to be 1367 ± 2 W/m2. Before that time, the solar alternations were estimated from observations of changes of the sunspots, or from measurements of the cosmogenic isotopes C-14 and Be-10 which can be found in different climate archives (tree rings, ice cores). The cosmic radiation leads to the formation of Be-10 and C-14 isotopes by conversing atmospherical nitrogen molecules. Since a high solar activity weakens the cosmic radiation, fewer C-14 and Be-10 isotopes are formed in times of high solar activity. Due to this counterbalancing link between solar activity and cosmic radiation, the production rate of the C-14 and Be-10 isotopes is also a measure for the activity and magnetic field of the sun in the past. The spectrum of the solar electromagnetic irradiation (Fig. 4.4) contains a broad wave range from short-wave x-rays to radio irradiation of several 100 m wavelength. The radio flux of 10.7 cm wavelength is an index which generally correlates well with the amount of sunspots, but which is also influenced by the strong magnetic fields of the sunspots (Solanki 2002). The origin of the varying solar activity are magnetic variations of the sun, as well as possible other processes like convection. Changes in solar activity are reflected in the frequency of sunspots. They appear more often when the sun is more active. Together with the sunspots, also solar flares and prominences appear (Fig. 4.1), which lead to an increase of the irradiance. Solar flares and sunspots have a lifetime of several weeks (Brönnimann 2004/05). Changes in the solar energy flux are an important climate forcing (Haigh 2001). Around one third of the radiation is reflected into space and does not contribute to the energy balance. Since the surface of the globe is four times bigger than its cross-section, of the 1367 W/m² and average of 342 W reach each square metre of the terrestrial surface, of which around 30 % are reflected back into space. The remaining 240 W/m2 are absorbed partly by the atmosphere, the ocean and the surface and warm up the earth. Consequently, 1 Watt altera- tion of solar irradiation per square metre effects the terrestrial energy balance with only 0.17 Watt. The solar insolation is not equally dissipated over the earth surface: whereas at the equator the average yearly value amounts to 426 W/m2, it amounts to only 176 W/m2 at the poles. This differing insolation is the foundation for the planetary circulation mechanisms of the atmosphere.

Fig. 4.4: Different measurements of solar activity, observed by satellites (a-d) or from the earth (e, f) in different time scales (a) x-ray irradiance, (b) UV irradiance, (c) total irradiance, (d) radio irradiance, (e) number of sunspots, (f) cosmogenic isotopes (C14, Be10), (from Lean 1998)

The 11-year cycle (Schwabe cycle) accounts for a fluctuation range of around 0.10 % of the solar constant, the Gleissberg cycle (80 years) for around 0.24 up to 0.30 %. The remaining cycles can be detected in the fluctuations of the solar irradiation in measurements of C-14 and Be-10 in tree rings and ice cores (Cubasch 2002). The lower stratosphere reacts differently pronounced to the varying solar irradiation, depending on the phasing of the QBO (quasi-biannual oscillation = a reversion of the wind in the stratosphere with a nearly two-year period (Labitzke and Loon 1999). In the stratosphere, Labitzke found temperature and pressure fluctuations in the same "rhythm" as the 11-year cycle of the sunspots (2003). According to Labitzke 2006, evaluations of the past 65 years confirm the influence of the 11-year sunspot cycle on the strength of the atmospherical polar vortex and the average meridional circulation. According to Mathes 2005, this has also significant impacts on the troposphere (vertical movement, precipitation, cloud formation). After extensive measurements of the isotopic frequencies of Be-10 and C-14 in ice cores from Greenland and the Antarctic, and after the evaluation of historical data, Usokin and So- lanki (Usokin 2003) have found a correlation between the number of sunspots and the temperature development. The number of sunspots reconstructed from these measurements goes back to the year 850. The evaluations showed that for the past 70 years the sun has been extraordinarily active. Another period of increased solar activity - but with a much lower number of sunspots - appeared to be in the Middle Ages from 1100 until 1250. For the complete examined period, the chronological sequence of solar activity shows great similarity to the development of the mean temperatures on earth. Yet, as the activity in the past years did not increase any further, according to Solanki it cannot be responsible for the temperature increase of the last 30 years. Meanwhile, Solanki/Usokin 2004 traced back the average number of sunspots until the year 9400 B.C. (Fig. 4.5) and found that the magnetic activity of the sun, which can be determined 37 from the number of sunspots, has not been as high for the last 8000 years as since around 1940. This was proven by extensive analyses of the C-14 content in tree rings from tree samples. The statement that from a statistical analysis of the length of periods with increased solar activity it could be possible to conclude the decrease of solar activity from its actual peak level within the next 50 years, could be of importance. The probability for it is said to amount to over 90 %. On the other hand, a stable, regular behaviour of the solar activity cannot be detected for the past. This is valid also for the connection between solar fluctuations and terrestrial climate. There is a relation on a regular basis, but it is often not really significant. Nevertheless, the Little Ice Age between 1645 and 1715 is easy to explain because in this period nearly no sunspots were observed.

Fig. 4.5: Number of sunspots reconstructed from C-14 data (10 -year mean values) for the past 11,400 years (blue graph) and the directly observed number of sunspots since 1610 (red graph) until 1900 (the end of reliable C-14 data). Thus, the strong increase since 1930 cannot be seen. The lower graph shows a detail with several episodes of solar activity which is comparable to today (BP = Before Present, BC = Before Christ) (Solanki 2004)

In his evaluation, Muscheler 2005 makes a slightly different statement than Solanki. Accord- ing to him, the solar activity probably was as high around 1150 and 1600 and in the late 18th century as shown by the satellite-based observations of the past 30 years. An evaluation of the fluctuations of luminosity from the records of sunspots and solar flares of the last 100 years proved an increase of the "solar constant" until 1940 by around 0.2 %, then a standstill until around 1970 which was followed by a light increase until today. Until 1970, this process corresponds relatively well to the development of the mean global temperature. Also model calculations by Stott 2001, 2003 have confirmed this connection. After the evaluation of the last two solar cycles from 1980 to 2002 by means of satellite data, Scafetta and West 2005 have found a tendency for the increase of the solar radiation of +0.047 % / decade. Consequently, only a minimal contribution of 10 to a maximum of 30 % of the global temperature increase could be expected from this for this period.

Discussion about the Solar Influence It is impossible to definitely prove temperature fluctuations in connection with the 11-year cycle at ground level - with 0.1 per thousand, the solar radiation fluctuations are very low. Nev- ertheless, changes in the stratosphere may possibly influence the troposphere. In the oceans, too, hints can be found for the effects of the 11-year sunspot cycle. Actually, experts discuss a positive feedback and with this an enhancement of the solar signal. First model results show for periods with increased solar irradiance a shift of the solar spectrum into the UV range. Here, the intensity fluctuations may even amount to 8 % (We- ber, Langematz, Labitzke 2001). This leads to a temperature rise in the stratosphere and to 38 an enhanced forming of ozone which in turn absorbs more solar radiation. Therefore, also the tropospherical circulation may change and influence our weather. The detection of this effect was promoted with the research project KODYACS which was supported by the German Federal Ministry of Education and Research (BMBF). A chemistry model was coupled with a climate model which contains a high resolution radiation parameterisation (AFO 2000, 2005). These models help to reproduce the variations related to QBO and the solar cycle. There is also a discussion about a causal connection between the sunspot activity and alterations of the Arctic and North Atlantic Oscillation (AO/NAO). Changes in the solar irradiance due to a decrease of the sunspots during the Maunder minimum at the end of the 17th century should have led to a temperature change of just 0.3 to 0.4 °C. Nevertheless, model calculations led to a temperature change - which was also observed - of 1 to 2 °C, which can be explained by alterations of the AO/NAO indexes (Shindell 2004). After correlation analysis, Boberg and Lundstedt 2002 assume that there is a connection between the solar wind and the NAO. The direct evaluation of the number of sunspots, as shown in Fig. 4.6, does not show an increase for the past 50 years. This means, it is no explanation for the temperature rise since 1975 (Solanki 2002, 2003, Usoskin 2004).

Fig. 4.6: Number of sunspots 1950-Feb 2007: no increase in the last 50 years (monthly average), (source: SIDC 2007)

4.1.2 Cosmic Particle Radiation and Geomagnetic Field Experts are intensively discussing the influence of the solar wind on our climate. Due to the solar wind, the sun loses around 1 million tons of its mass per second. The strength of the solar wind which consists mainly of protons and electrons, depends on the solar activity and deforms the solar and geomagnetic fields, because it consists of electric particles (Fig. 4.7). The solar wind influences on its part the galactic cosmic irradiation. A high solar activity leads to a reduction of the cosmic irradiation which reaches the earth, because the magnetic field which shields the earth from the cosmic radiation strengthens, too. From this follows that the production of cosmogenic isotopes in the atmosphere is inversely proportional to the strength of the solar activity. 39

Fig. 4.7: The geomagnetic field of the earth deflects the solar wind and weakens the cosmic irradiation which penetrates the earth (www.esa.int/esaCP/ESAFM97708D_Germany_0.html ), (source: NASA)

According to an intensely discussed model of Danish researchers (Friis-Christensen 1991, Svensmark 1997), which was further refined, the ions created by the cosmic irradiation serve as condensation germs for bigger floating particles (clusters) and thus promote the formation of clouds. Consequently, with reduced solar activity the increased cosmic radiation in the terrestrial atmosphere should cause an intensified cooling, because due to the higher number of particles more clouds are formed. The micro-physical process which may influence the atmospherical process of the formation of aerosols due to cosmic irradiation, was in fact confirmed, but the extent of this influence is uncertain (Gray 2005).

Fig. 4.8: The course of the cosmic irradiation in Climax, Colorado (one of the longest series of measurements) and the temperature of the terrestrial surface since 1953 (gliding mean value over 11 years). The cosmic irradiation is shown to be decreasing in upper direction, because according to the theory a decrease of the cosmic irradiation should lead to an increase of the temperature. The course of the cosmic irradiation could theoretically explain more or less the course of temperatures until 1980, but not the subsequent strong temperature increase (data: NOAA (cosmic irradiation), Cru (temperature), graph: ProClim)

The correlation between the solar cycle or the cosmic irradiation and cloud formation, as assumed by Danish researchers (Friis-Christensen and Lassen 1991, Marsh and Svensmark 2001), could not be verified so far in this form (Laut 2003, Sun 2004). But it is assumed that there are causal connections between the temperature change and the regionally differing coverage grade of low-lying, but also high-lying clouds. Different studies find partly differing 40 results (Thejll 2000, Carslaw 2002, Laut, Sun 2002, Bradley 2004, Marsh 2004,Todd 2004, Usoskin 2004, 2005, Pallé 2005). As the study by the Hadley Center 2005 (Gray 2005) conducted for the 4th IPCC report has shown, the contexts are much more complex. Meanwhile, it was possible to prove the theoretical connection between cosmic radiation and cloud formation, but it is valid only for those regions where condensable water vapour is present without substantial competing condensation particles (Gray 2005). Yet, the geographical dispersion of this particle formation and its frequency are unknown. This statement remains un- touched, too, by the findings of the new experimental study by Svensmark 2006, according to which in reaction chambers negative ions form aerosol clusters which can be considered to be the pre-stage of condensation nuclei for the formation of clouds. As shown in Fig. 4.8, the temporarily existing connection between the temperature increase and the decrease of cosmic irradiation in the 80s of the 20th century did not continue, so that at least for the last 20 years the cosmic irradiation cannot be made responsible for the global temperature rise (http://www.proclim.ch/Products/ClimatePress/ClimatePress19D.pdf). This is true also for the solar irradiation. Whereas for the first half of the 20th century there was a parallel increase of the temperature and the solar irradiation, this is not true anymore from 1970 onwards (Fig. 4.9). The global temperature increase of the last 30 years cannot be explained by this theory either, because the solar irradiation remained more or less constant for the last 60 years, although on a high level (Wirsing 2003, Krivova 2004, Foukal 2006).

Fig. 4.9 Total solar irradiance and terrestrial temperature vs. time for irradiance reconstructions with an increase in the 11- year averaged irradiance between 1700 and 1980 of 4 Wm-2. The blue curves prior to 1985 represent irradiance reconstructions (solid curve: cycle-length based, dashed: cycle-amplitude based). From 1985 onwards they represent total irradiance measurements. The red curves represent global (solid) and northern hemisphere (dashed) temperatures. All curves have been smoothed by an 11-year running mean. (http://www.mps.mpg.de/projects/sun-climate/resu_body.html)

Another extraterrestrial theory, published by Shaviv and Veizer in 2003, establishes a connection between global temperature and cosmic irradiation. Since our solar system moves through the spiral arms of our galaxy over periods of hundreds of million years (Fig. 4.10), the galactic cosmic radiation flux is said to change and thus influence the terrestrial temperature by means of the formation of clouds (intensity cycle of the cosmic irradiation of around 143 million years). In 2004, Rahmstorf et al. have investigated this theory and could not con- 41 firm this context. Shaviv and Veizer have also confirmed that their theory applies to a time scale of millions of years and that it is not suitable for shorter cycle times (Rahmstorf 2004). Many German and Swiss climate scientists have published a statement (24.10.2003, PIK) according to which this theory, which is based on long-term geological periods, is referred to as not being relevant for the actual climate discussions which are based on periods of decades.

Fig. 4.10: Our solar system situated in the spiral arms of the Milky Way, green point = actual position of our solar system (http://www.staff.uni-mainz.de/bpfeiffe/Vhs04f-w.pdf)

To sum up, it can be stated that the sun decisively influences our climate (Cubasch 2002, 2006). The IPCC 2001 (TAR) assumes that its share in the global warming amounts to around 20 % for the 20th century; in the AR4 the radiative forcing 1750 – 2005 was halved compared to the TAR (SPM, IPCC 2007). Clausen 2003 assumes 25 to a maximum of 40 %. It does not enable us to explain the warming of the past 30 years. Basically, the scientists do not exclude "that in the future it will be possible to identify indirect solar working mechanisms (e.g. solar wind). Yet, it seems to be improbable that the indirect effects of the solar radiation intensity should be much stronger than the direct effects which already today are part of the models and explain the past quite well (Solanki 2003).

4.2 Volcanoes

Explosive volcanic eruptions emit big quantities of solid matters and gases (several million tons) into the atmosphere (Fig. 4.11). Apart from volcanic ashes, there are also considerable amounts of gases like water vapour, sulphur dioxide, hydrosulphide (H2S), carbon dioxide, HF, HCl, etc. Particularly finest volcanic ashes and sulphate aerosols that reach the stratosphere can influence the climate by 1 to 3 years due to their long life span. The aerosols not only absorb the short-wave solar irradiation, but also the terrestrial long-wave infrared radiation of the earth. Additionally, they disperse the incident sunlight. Generally, the net effect of this change in the radiation budget (Fig. 4.12) is a warming of the stratosphere and a cooling of the terrestrial surface near ground level (Schönwiese 2003, 2005b). 42

Fig. 4.11 Eruption of Mt. Pinatubo 1991: huge amounts of gases and aerosols are ejected even into the stratosphere (http://earthobservatory.nasa.gov/Library/UVB/uvb_radiation3.html)

After the big volcanic eruptions of the 20th century (like e.g. Mt. Pinatubo in 1991 (fig. 4.11), the summer temperature decreased, and the winter temperature increased. For two years, the earth had globally cooled down by about 0.5° C (Robock 2000, 2002). In the case of big volcanic eruptions in high latitudes (e.g. Mt. Katmai, Alaska 1912), the aerosols stay in the hemisphere where they have been emitted (Oman 2005) and cause a significant cooling and decrease of the Asian monsoon, which in consequence leads to a temperature increase in Northern India. Evaluations of the last 500 years have shown also that big volcanic eruptions may cause El Niño events (Adams 2003, Brönnimann 2004/05). Volcanic aerosols do not only influence the radiation flux in the stratosphere, but also chemical processes like the ozone formation and destruction. This leads to a reduced thickness by 3 -10 % of the ozone layer for a period of 1 - 2 years (Bissolli 2001). After the eruption of Mt. Pinatubo in 1991, a reduction of the total ozone of up to 7 % was measured which lead to an enhanced UV irradiance at ground level (Graf 2002). Due to the emerging stronger temperature gradient of the stratosphere, the polar vortex is enhanced which tends to lead to a higher NAO index. 43

Fig. 4.12: Changes of the radiative forcing amounting to 3 – 4.5 W/m2 after big volcanic eruptions for 1 - 2 years in each case (Grieser 1998)

4.3 North Atlantic Oscillation - NAO The North Atlantic Oscillation (NAO) is one of the dominating oscillation patterns of natural climate variability of the Northern hemisphere (Hurrell 1995). It is a more or less regular change of the atmospherical circulation (atmospheric pressure fluctuations) on the Northern hemisphere which strongly influences the weather and climate in Europe and North America. The NAO describes the fluctuations in the atmospheric pressure relation between the Iceland Deep in the North and the Azores High in the South of the Atlantic. The measuring unit is the NAO index. It is defined to be the difference of the standardised pressure anomalies of Ponta Delgada (Azores) and Reykjavik (Iceland). There are further NAO indices. If the NAO index is positive, the atmospheric pressure over Iceland is very low, and the one over the Azores is very high. In the case of little pressure differences, the NAO index becomes negative (Fig. 4.13). Mainly in winter the NAO is pronounced, in the other seasons it is rather weak. A continued positive anomaly of the NAO, i.e. an increased atmospheric pressure contrast, causes an enhanced supply of cold air to the west of Greenland and the warming of this air over the North Atlantic. The West Wind Belt is intensified, and a bigger amount of warmth can be released from the water into the air. The biggest pressure amplitudes appear in winter (Cassou 2001). The North Atlantic Oscillation has a particular influence on the weather in Europe and Northeast America (Fig. 4.14). Consequently, the influx of Siberian cold air to Europe is suppressed, and the winters in Western Europe and at the East Coast of the USA are observed to be mild. In contrast thereto, it is particularly cold and dry in the North of Can- ada and in Greenland (maritime phase). A continued negative anomaly of the NAO - a relatively low pressure difference in winter between the Azores and Iceland - leads to a weakening of the West Wind Belt over the North Atlantic, the influx of mild, humid Atlantic air masses to Western Europe is reduced, and the cold and dry air from Siberia leads to hard winters in Western Europe. It is cold at the East Coast of the USA, and Greenland has a mild winter (continental phase). Fig. 4.15 shows the course of the winter North Atlantic Oscillation Index (NAOI) since 1825. Clearly visible are the 10-year fluctuations and a tendency from a negative to a positive NAOI for the period between 1960 and 1990. Comparisons with NAO reconstructions for the past 350 years show that there were interdecadal fluctuations, but the increase until the mid 1990s was extraordinarily strong. Consequently, these winters were - like at the beginning of the 20th century - extraordinarily warm. The mild European winter 2006/07 showed also a strongly positive NAO index (Nov. +1.70, Dec. +3.08, Jan 2007 +1.77). Obviously, the NAO is closely linked to the Arctic Oscillation (AO), an extensive oscillation of the atmosphere which is characterised by contrasting air pressure anomalies in the Central Arctic and parts of the mid-latitudes (Rind 2005). By the variations of the atmospheric pressure at sea level in the Arctic Ocean, the Arctic Oscillation is permanently positively correlated to the NAO. Addi- 44 tionally, there is a connection between the anomalies of the water surface temperature during the Pacific El Niño event (Wang 2005) and the Indian summer monsoon (Goswani 2006).

Fig. 4.13: Model of the positive and negative phase of the North Atlantic Oscillation (NAO). The arrows show the flux system within the ocean and the atmosphere (from Wanner et al. 2001)

A positive NAO index does not only have effects on the atmosphere and the ocean, but also on the ecosystems. In Greenland, it is particularly cold and dry. Strong storms reach North- ern Europe, heavy precipitation and mild temperatures are its consequences in Central Europe. The ice export from the Arctic increases. The Labrador Sea becomes particularly cold, the Gulf Stream is warming up. The intensified trade winds lead to a cooling of the equatorial Pacific. As a consequence, the fish population (codfish) in the Labrador Sea di- minishes. In contrast thereto, the fish proliferate off the African coast because the nutrient- rich deep sea waters rise up (www.ifm-geomar.de/index.php?id=oz-on_nao#8516).

Fig. 4.14: A positive NAO leads to mild and warm European winters (left), a continued negative NAO phase to severe and cold European winters (right) (Hagen 2003) 45

Fig. 4.15: Anomalies of the North Atlantic Oscillation Index 1825 – 2005/6. Noticeable are the very low values of the 1960s, and the high values around 1990, which were linked to mild winters, the NAO Index for winter 2006/07 was strongly positive (Dec 2006 +3.08!) (http://www.cru.uea.ac.uk/~timo/projpages/nao_update.htm)

Already in 1996, Hurrell demonstrated the correlation of the NAO tendency with the temperature rise in Europe. Correlation studies have unambiguously confirmed the influence the NAO has in winter on the air temperature range in Europe (Tinz 2002).

Discussion of Possible Causes for NAO Changes According to Hurrell 2003, the NAO is a large-scale atmospherical phenomenon which arises from the stochastic interactions of different climate elements. Although the NAO is an internal variability of the atmosphere, stratospheric and anthropogenic processes may influence the phases and amplitudes of the NAO (Hurrell 2003). At present, the experts discuss different mechanisms: Changes in the tropical warming rate influence the atmospheric circulation, and the tropical convection reacts to changes of the water surface temperature below it, which on its part effects the NAO (Hoerling 2001). A second possibility are interactions with the lower stratosphere. A third possibility is an influence on the NAO by a heat exchange between atmosphere and oceans, sea ice and/or continental system (Visbeck 2002). At present there is no consent about which process or which processes influence the NAO most of all. The majority of the model results show that the oceanic currents, extratropical and tropical temperature changes of the surface water are some of the forcings of the NAO fluctuations. The comparison of 17 coupled ocean-atmosphere models within the framework of the project on the comparison of models (CMIP) has shown that increasing greenhouse gas emissions cause a certain enhancement of the NAO towards a positive index (Stephenson 2003, Osborn 2002, 2004, Kuzmina 2005). After having made some model calculations, Scaife 2005 explains part of the strong positive NAO winter tendency between 1965 and 1995 with a coupling of the observed stratospheric circulation changes. On the other hand, these changes in the stratosphere may also have been caused by a positive feedback from the troposphere. Statistical evaluations by Blessing 2005 also indicate interactions between the stratosphere and the troposphere. Increasing greenhouse gases in the troposphere, and decreasing ozone in the stratosphere, enhance the meridional temperature gradient in the lower stratosphere which leads to a stronger polar vortex, a phenomenon which could also be observed. This could have influenced the positive NAO tendency (Hurrell 2003, Plumb 2003). Model calculations which take into account greenhouse gases and aerosols have also shown an increase of the NAO, but the observed increase is significantly bigger than the calculated one. This shows that today's climate models are unable to simulate this important aspect of a large-scale climate change (Gillett 2005). In the past years, the winter NAO has weakened compared to the beginning of the 1990s. In the past three winters, it was slightly negative (Fig. 4.15); also the winter temperatures in Central Europe were slightly higher than the mean values, but did not rise further compared to the beginning of the 1990s. 46 A new AWI model calculation (Dethloff 2006) with an improved ocean/atmosphere model, which takes into consideration the increased reflective behaviour of solar irradiance in the Arctic, predicts a clear change of the weather conditions in the North Atlantic region. Due to the ice - albedo feedback as a consequence of the warming of the Arctic, the energy flux in the Arctic will be reallocated. This will also change the NAO. The improved models predict a tendency towards a negative NAO phase. This could lead to dry and cold winters in the future. Generally, the contribution of the NAO to the Eurasian temperature rise in winter in the last 30 years is estimated to amount to 30 - 50 % (Thompson 2000, 2001). According to Schnur 2003, there are still discussions about how to interpret the NAO tendency since the beginning of the 1960s, and the AO coupled to it, as well as about a possible anthropogenic influence on it.

4.4 Southern Oscillation El Niño – ENSO The strongest natural climate fluctuation for periods of some months up to several years, is the El Niño/Southern Oscillation Phenomenon (ENSO). El Niño and La Niña are phenomena of the tropical-pacific weather which fundamentally change the circulation in the Pacific. These circulation fluctuations in the tropical ocean (Fig. 4.16) are atmospherically closely correlated to the so-called Southern Oscillation (SO), a kind of air pressure oscillation between the South East Asian deep and the South West Pacific high (of the tropical/subtropical Southern hemisphere) (Schönwiese 2005, Wang 2002, 2005).

Fig. 4.16: Simplified scheme of El Niño (http://www.elnino.info/k1.php)

El Niño is characterised by an extraordinary increase of the ocean surface temperatures of more than 5 °C along the equator, starting off the Peruvian coast and spreading into the central Pacific (Fig. 4.17); normally these areas are very cold. This weakens the Southeast trade wind. In the case of El Niño, the equatorial Western Pacific - normally with high precipitation - is extraordinarily arid, whereas due to the increased evaporation above the warmed water surface of the Eastern edge of the ocean (Peru), precipitation increases. The intervals between two El Niño events are irregular, they appear every 3 to 7 years and last for around 12 -18 months. El Niño is mostly followed by La Niña after a transition phase. This cold event is characterised mainly by an enhanced normal situation. 47

Fig. 4.17: Abnormal water surface temperature in °C during the extraordinarily strong El Niño event of 1997/98 off the West coast of South America (source: NCEP)

El Niño is a natural phenomenon which has been appearing for millenniums. The most important - and largely secured - global consequences of El Niño are: - Increase of precipitation in the Eastern, and decrease in the Western equatorial pacific - Increase of tropical storm activities in the Eastern North Pacific - Decrease of hurricane activities in the Atlantic Ocean - Aridity in the Caribbean and Central America - Higher precipitation in the Southern USA and Eastern Africa - Droughts in the Northeast of Brazil and Southeast Asia Consequently there are many reports about crop failures, a decrease of fishery, coral bleaching, droughts, storms and floods in many parts of the world (Asia, Africa, South America). During the strongest El Niño event of the past 25 years in 1997/98, the USA have profited from it by milder temperatures (less heating costs). Very strong El Niño events (slightly) influence the weather in Europe, as Brönnimann has proved in 2004. Thanks to coupled climate models, it is possible today to predict El Niño events some months in advance (Latif 2003).

Discussion of the Possible Influence of the Global Warming Science discusses how far the global warming influences El Niño, or whether vice versa El Niño effects the global mean temperature, or whether the observed temperature rise of the last 30 years is at least partly due to an increased number of El Niño events. According to Sun 2003, the increase of the water surface temperature observed since 1976 in the tropical Pacific of 0.3 to 0.4 °C points to this fact. A significant causal connection exists between the ENSO phases and the global mean temperature. According to Tsonis 2003, a global temperature change caused by natural fluctuations and/or increased greenhouse gas concentrations is an important input for the variabilities of the El Niño phenomenon. Nevertheless, model calculations within the framework of the Coupled Model Intercomparison Project (CMIP) did not show unambiguous results towards an influence on the frequency of El Niño events (Collins 2005). This is also true for the 15 coupled climate models of the AR4 report (Merryfield 2006).

4.5 Thermohaline Circulation (THC) The broad oceanic circulation is determined by the wind field, as well as by heat and fresh water currents at the surface. The global pattern of the heat flux leads to the absorption of heat at the Equator which is released again in the polar region. 48 Together with the deep sea currents, the surface currents of the oceans are part of a current system which comprises all three oceans. It is called the Great Conveyor Belt and it reaches from the North Atlantic via the Antarctic Circumpolar Current and the Indian Ocean into the Northern Pacific and back (Fig. 4.18). Due to its most important forcing factors temperature and salinity, it is also called "thermohaline circulation” (THC). An important motor of the THC is the thermohaline induced sinking of cold and salt-rich water in the North Atlantic current which is a continuation of the Gulf Stream. The biggest sinking region lies between Norway and Greenland, another important one off the Antarctic in the Weddell Sea. In return, warm surface water streams north. The THC is part of the North Atlantic Meridional Overturning Circulation (MOC), which comprises the complete North-South drift over the complete width and depths of the ocean, including also the wind-driven part (http://www.clivar.ucar.edu/organization/atlantic/THCwrkshp.pdf ). The precise reason for this global circulation is the higher salinity (1-3 ‰) of the Atlantic compared to the other oceans, which is due to the stronger evaporation and, with this, the higher density. The warm water of the surface which flows north gives off its heat to the air. It cools down and, due to the evaporation or freezing, becomes saltier and denser. It sinks down and flows southwards within a depth of 2 to 3 km. In the deep, the dense Atlantic water flows into the two other oceans, and lighter surface water flows back into the Atlantic.

Fig. 4.18: Strongly simplified scheme of the global system of ocean currents (great conveyor belt, thermohaline circulation) with cold deep sea currents (blue) and warm surface currents (red) (Rahmstorf 2002)

Discussion of Possible Changes of the THC Over the past few years, experts have intensively discussed whether the global warming would change this circulation and (irreversibly) disrupt the deep sea current. This would lead to an icing of the Northern seas and to a global cooling with a deep impact on Europe. Re- cent model simulations show a differentiated behaviour, and only a small danger of a disruption of the marine conveyor belt and, with this, the absence of the Gulf Stream in the forthcoming decades. Even if the CO2 concentration quadrupled, the circulating force would decline by only 10 to 50 %. No model showed a quick or complete collapse (Gregory 2005). For 2100, the model calculations of the MPI-M 2006 for the AR4 have shown a decrease of around 30 % of the large-scale North Atlantic circulation (see chapter 8.2.3). Based on measurements in the ocean and model calculations, Latif 2006 cannot find a severe weaken- 49 ing of the THC and establishes that in the next decades it will probably continue to exist within the natural climate variability. By means of measurements between 1957 and 2004, Bryden 2005 reported that the Atlantic Meridional Oscillation Circulation (MOC) - the THC is a part of it – seems to have weakened by around 30 % in the last decade. Although the uncertainty about the extend of this decrease is high, the decreasing trend is statistically significant. This decreasing trend would be in line with the results of the computer models of a warming planet. Model calculations (Jacob 2005) with a weakening thermohaline circulation (THC) by half result in changes of the atmospherical circulation and a cooling of the North Atlantic surface by around 3 °C. This leads to lower winter temperatures in Northern Europe around 1.5° C and to increased snowfall in winter. Moreover, the already observed enhanced flow of fresh water from the rivers into the Arctic Ocean (WU 2005) could influence the THC.

4.6. Natural Greenhouse Gases Due to the radiative forcing of the climate relevant, natural trace gases in the atmosphere, the mean global temperature near ground level rise from -18 °C to around +15 °C. This so- called natural greenhouse effect is caused by the absorption and re-emission of longwave terrestrial heat radiation in the atmosphere. The most important natural greenhouse gases are water vapour, CO2, CH4, O3 and N2O (see chapter 3.3). The share of the natural trace gases in the greenhouse effect is shown in Fig. 5.2 of chapter 5.1. 50

5 Anthropogenic Influencing Factors on the Climate The human being is part of the biosphere, and just by his mere existence he inevitably influences his environment, and with this the climate system. The continued increase in the world population since the Stone Age, and the fact that humans settled down several thousand years ago, already influenced the climate because it required the clearing of woods due to the transition from nomadism to agriculture. The first systematic deforestation took place at the time of the Roman Empire in the Mediterranean, when e.g. the Apennines were nearly completely cleared of trees for shipbuilding purposes. In the past 8000 years, mankind has cut down nearly half of the forests in order to make the ground arable (Brovkin 2004). Be- tween 800 and 2000 A.D., the share of forest declined from 90 to around 31 % in Germany. In the same period, the arable land increased from 5 to 38 %. This causes a change in the reflectory properties (albedo) of the terrestrial surface. The draining of swamps reduced the methane emissions, but the rice cultivation increased it again. Urban growth increased the sealing of the landscape. With the beginning of the industrialisation, man started to change the atmospheric composition now on a large and global scale. It is possible to prove the increase of the carbon dioxide and methane content in ice cores for the past 200 years. To this add new and artificial compounds, like e.g. CFCs, which destroy the ozone layer in the stratosphere and contribute to the global warming (Wagner 2004, supplemented by the author). Fig. 5.1 gives an overview of the anthropogenic influencing factors on the climate (Wagner 2004).

Anthropogenic Changes Effects on the Climate System Slash-and-Burn Changes of the terrestrial surface, emission of 1) trace gases like CO2, CO, NOx , CH4, CH3Cl and aerosols Agriculture Changes of the terrestrial surface, emission of trace gases like CH4, N2O, NH3

Livestock production Emission of trace gases like CH4, NH3, H2S 1) Combustion of fossil energy Emission of trace gases like CO2, SO2, NOx , CO, sources HCl and aerosols

Waste disposal Emission of trace gases like CO2, CH4 Artificial building Changes of the terrestrial surface (e.g. changes of the albedo, of air currents near ground level and of the water balance) Industrial processes Emission of multiple, partly artificial trace substances and aerosols 1) Air traffic Emission of trace gases like CO2, SO2, NOx , CO, HCl, direct changes of the cloudiness Regulation of inland waters Change in the water balance

1) NOx = NO + NO2

Fig. 5.1: Anthropogenic changes and their effect on the climate system. In addition to changes of the terrestrial surface, also trace gases and aerosols, the albedo, the water balance and cloudiness are changed (Wagner 2004)

5.1 Anthropogenic Greenhouse Gases

The most important greenhouse gases are water vapour (H2O), carbon dioxide (CO2), methane (CH4), ozone (O3), dinitrogen monoxide (N2O), and the F-gases (CFCs, H-FCs and SF6.) Their contribution to the anthropogenic greenhouse effect amounts to 4 % for N2O and 61 % 51 for CO2 (see Fig. 5.2). Additionally, there are also some precursor substances (indirect greenhouse gases) like nitrogen oxides, organic compounds (NMVOC) and carbon monoxide, which are of paramount importance for the atmospheric chemistry and the formation or destruction of greenhouse gases, like ozone and methane. The World Data Center for Greenhouse Gases (WDGCC) collects data about the regional and global development of the greenhouse gases (http//gaw.kishou.go.jp). Fig. 5.2 outlines the most important properties of the climate-effective trace gases (greenhouse gases) with emissions and concentrations (for 2006 each, pre-industrial concentrations around 1800 in brackets), with an estimate of the contributions to the natural (second column to the right) and anthropogenic greenhouse effect (right column) (Schönwiese 2006, supplemented). In 2006, the CO2 concentration rose up to 381 ppm. According to this figure, CO2 accounts for around 61 % of the anthropogenic greenhouse effect, CH4 for around 15 %, CFCs for around 11 %, N2O for around 4 % and O3 for around 9 %. The most important human activities which emit greenhouse gases are, next to the combustion of fossil fuels, the clearing of forests, agriculture, landfills and certain industrial processes. Fig. 5.2 also sums up the sources of the anthropogenic greenhouse gases (Schön- wiese 2006). The share of the anthropogenic CO2 emissions of around 75 % of fossil energy comprises the sectors power industry, industry, household and traffic. Trace gases overview Trace gas, symbol Anthropog. Atmospheric Greenhouse effect emissions Concentrations Natural Anthrop.

Carbon dioxide, CO2 30 Gt/yr 381 (280) ppm 26 % 61 %

Methane, CH4 300 Mt/yr 1.8 (0.7) ppm 2 % 15 % CFC 0.4 Mt/yr 0.5 (0) ppb - 11 %

Nitrous oxide, N2O 15 Mt/yr 0.32 (0.27) ppm 4 % 4 %

Ozone, O3 370 Mt/yr 34 (25) ppb 8 % 9 %**

Water vapour, H2O rel. small 2.6 (2.6) %* 60 % (indirect) Classification of anthropogenic emissions

CO2: 75% fossil energy, 20% forest clearings, 5% use of wood (part. devel. countries)

CH4: 25% fossil energy, 28% cattle raising, 11% rice cultivation, 4 % manure, 13% solid waste, 10% sewage water, 9% biomass combustion, CFC: Propellant in dispensers, refrigeration, insulating material, purification

N2O: 86% agriculture (including fertilisation), 5% chemical industry, 6% fossil energy, 1% biomass combustion, 2% human sewage

O3: indirectly via precursor substances (e.g. nitrogen oxides NOx, traffic) (Many sources, a.o. IPCC, 2001, Lozen et al., 2001, here according to Schönwiese, 2003)

*) Mean value near ground level **) With further gases

Fig. 5.2: Overview of the trace gases and their contribution to the greenhouse effect, with summary of their emission source, pre-industrial values in brackets (supplemented 2007, source: Schönwiese 2006, EPA 2006)

Since the beginning of industrialisation, the greenhouse gas concentration in the atmosphere has increased at different rates (Fig. 5.3 (since around 1978)). In the past years, it has been possible particularly for the various CFCs to either heavily reduce their increase, or to see their amount decrease. There has also been a clear decline in methane increase. In the past 30 years, the carbon dioxide concentration has risen on an average by around 1.5 ppm per year. 52

Fig. 5.3: Development of the mean global concentrations of the most important, well-mixed and long-living greenhouse gases between 1978 and 2005, data from the global data collection network of the NOAA. These gases account for 87 % of the radiative forcing of the long-living greenhouse gases since 1750 (www.cmdl.noaaa.gov/aggi/)

Between 1970 and 2005, the global greenhouse gas emissions continuously increased (see also chapter 10). Fig. 5.4 clearly shows the contribution of the deforestation to CO2 emissions, and the big share of agriculture in methane and N2O emissions. The share of F-gases amounts to around 1 %.

Fig. 5.4: Trend in global emissions of the greenhouse gases CO2, CH4, N2O, F-gases in Pg t (= billion t) CO2eq from different sectors (source: RIVM/MNP, http://www.mnp.nl/edgar/Images/Olivier2005-FT2000-NCGG4-Utrecht_tcm32- 22124.pdf) 53 For the period between 1990 and 2004, the total emissions of the industrialised countries (annex I) have decreased by 3.3 %, and those of the Kyoto Protocol Member states by 15.3 % (at present 35 states) (UNFCCC 2006). Between 1990 and 2005, the greenhouse gas emissions within the EU25 declined by 5.6 % from 5261 Tg to 4968 Tg CO2 equivalents (Fig. 10.1) (DIW 2006). Since 2000, they have again slightly increased (around 2 %).

Fig. 5.5 shows the development of direct and indirect greenhouse gases, as well as of SO2, for the period 1990 – 2004 in Germany. With the exception of HFC, it was possible to achieve significant reductions for all gases within this period. Chapter 10 refers to the contribution of the power industry.

1990 1995 2000 2003 2004

CO2 1030231 920155 886258 892545 885854

CH4 4752 3893 3091 2675 2450

N2O 273 251 192 201 207 HFC * 4369 6555 6556 8487 8802

CF4 [Mg] 357 222 71 80 76

C2F6 [Mg] 42 32 25 23 22

SF6 [Mg] 200 302 213 180 187

Sum of CO2 1226671 1095116 1023219 1024800 1015692 equivalents

NOx 2884 2140 1865 1616 1566 (as NO2) NMVOC 3585 2100 1513 1212 1234 CO 12095 6409 4994 4313 3668

SO2 5322 1713 633 599 562

* Concentrations in [Gg = 1000 t], with the exception of CF4, C2F6 and SF6 [Mg]

Fig. 5.5: Development of the emissions of direct and indirect greenhouse gases and SO2 in Germany for the years 1990 to 2004 in 1000 t (Gg)and tons (Mg) (source: NIR 2006) It is possible to calculate the increase in radiative forcing, which is so important for the greenhouse effect, from the increase rates of the greenhouse gases. Fig. 5.6 shows the average increase rates of the radiative forcing of the greenhouse gases (CO2, CH4, N2O, MPTGs (Montreal Protocol of greenhouse gases)) between 1958 and 2003. The decrease in the growth of the increase rates is essentially due to the CFC phase-out on account of the Montreal Protocol at the end of the 1980s.

2 Fig. 5.6: Yearly increase rate of the radiative forcing in W/m /a of the well-mixed greenhouse gases; in 2003, CO2 had a share of around 90 %, and since 1995, the MPTG (Montreal Protocol Gases) haven't been of importance anymore (Hansen 2004d)

Up to now, the decrease in methane is not yet completely understood. The breakdown of the Eastern Bloc had a temporary clear effect on carbon dioxide. After a clear decrease at the beginning of the 1990s, the increase rates of the radiative forcing of the well-mixed green- 54 house gases have risen globally in the past years in particular due to CO2, as the graph below (Fig. 5.6)shows (Hansen 2004d, Hofmann 2005). The radiative forcing of the greenhouse gases, which is significant for the climate, has continuously increased (Fig. 5.7). Since 1990, the total radiative forcing has risen by over 21.5 % (AGGI = 1.215) (just CO2 by around 28 %). The yearly greenhouse gas index (AGGI) as defined by the NOAA was set to be 1 for 1990, the baseline year of the Kyoto Protocol.

Fig. 5.7: Radiative forcing of the long-living greenhouse gases for the period between 1979 and 2005, related to 1750. Since 1990, the radiative forcing of carbon dioxide has increased at 28 %, whereas the increase in the case of methane has slowed down and that for the CFCs has decreased. The AGGI index (right side) states the percentage increase of the total radiative forcing since 1990. 1.215 means an increase at 21.5 % (www.cmdl.noaa.gov/aggi)

5.1.1 Water Vapour (H2O) Water vapour is the main absorbing substance of the heat radiation in the atmosphere. In the atmosphere, water vapour is contained by an average 0.3 % of the masses, carbon dioxide by 0.06 %, which means that water vapour corresponds to around 80 % of the greenhouse gas masses in the atmosphere (around 90 % of its volume). With a contribution to the greenhouse effect of between 36 % and 66 %, water vapour is the most important greenhouse gas. Together with the clouds, its contribution even amounts to as much as 66 % to 85 %. On the other hand, water vapour has only a short residence time of around 10 days in the troposphere. As far as the anthropogenic greenhouse effect is concerned, water vapour also has a secondary effect because it increases evaporation due to elevated temperatures. IPCC 2001 states that the anthropogenically caused water vapour increase causes an additional warming of around 50 %. Therefore, water vapour leads to a positive feedback for the greenhouse effect. A part of the measured increase of water vapour in the stratosphere - 75 % in the past 40 years - is due to methane, which has increased, too, because it oxidises to water vapour and carbon dioxide in the stratosphere. The models for the feedback mechanisms take into account the important role of water vapour. Climate models and empirical studies calculate a positive feedback factor for water vapour of 1.3 to 1.7 (Bengtsson 2004). 55

5.1.2 Carbon Dioxide (CO2) Carbon dioxide is an important greenhouse gas and is, next to water vapour, the second strongest contributing gas to the greenhouse effect. On the terrestrial surface, CO2 is emitted and absorbed in manifold ways: absorption and photosynthesis by the terrestrial biosphere, exchange with the oceans, and human activities like the combustion of fossil fuels or changes in the land use (e.g. clearings made by burning). Different processes which progress on varying time scales, remove the carbon dioxide from the atmosphere. With an average of 100 years, its residence time is relatively long. Being the reference gas, carbon dioxide is defined to have a global warming potential of 1.

CO2 Concentrations in the Atmosphere

Since the beginning of industrialisation, the carbon dioxide (CO2) level in the atmosphere has risen by about 35 % (Fig. 5.8 (right)). The annual increase in the concentration for the last two decades amounted to approx. 0.4 %. In 2006, the average global concentration in the atmosphere increased at 2.3 ppm and rose to 381 ppm (0.0381 %). The global increase rate varies strongly on an annual basis (0.9 – 3.1 ppm), and in the period between 1960 and 2005, the average was 1.4 ppm/year. During the last ten years (1995 – 2005) it rose to 1.9 ppm (Fig. 5.8). The highest increase rates (2 - 3 ppm/year) were found in years with warm El Niño Southern Oscillation events (ENSO), but also in 2002, 2003, 2005 and 2006. The lowest increase rate (0.4 ppm/year) with partly negative augmentations in the Northern latitudes was found in 1992 after the eruption of Mt. Pinatubo in 1991. An increase of 1 ppm of CO2 in the atmosphere corresponds to the masses of 2.1 billion t of carbon.

Fig. 5.8: left: Global carbon dioxide mixing ratio and growth rates betwee1980 and 2004; the yearly average value of 1.5 ppm varies between 0.9 and 3.1 ppm. (Hofman 2005), right: development of CO2 concentration in the last 10,000 years (SPM, IPCC 2007) Ice core measurements in Antarctica carried out in the framework of the EPICA Project (European Project for Ice Coring in Antarctica) have shown that the current carbon dioxide concentration of 381 ppm is the highest for 650,000 years (Siegenthaler 2005). The seasonal fluctuations are high in the Northern hemisphere and low in the Southern hemisphere. The fluctuations in the Northern hemisphere reflect the absorptions and emissions of the biosphere, whereas the fluctuations in the Southern hemisphere reflect, additionally to the influence of the biosphere, changes in the sea and the burning of biomass (WDCGG, March 2006, http://gaw.kishou.go.jp/wdcgg.html).

Numerous measurement stations around the globe measure the atmospheric CO2 increase and its seasonal fluctuations. Figure 5.9 shows the measurement stations Schauinsland in the Black Forest, Zugspitze (Germany) and Mauna Loa, Hawaii. 56

Fig. 5.9: Trend of the global CO2 concentration for the period between 1958 and 2005 for the measurement stations Mauna Loa, Hawaii, Zugspitze and Schauinsland, Germany (Ries 2006)

Due to the good intermixture in the atmosphere (mixture time of some days to some weeks in the troposphere), the concentrations vary only slightly in terms of area and time. The annual course of the monthly values, with a peak in springtime and a minimum in the later summer/early autumn, is caused by the interactions of the biological activity, the combustion of fossil fuels and the altitude of the mixing layer. From springtime until early autumn, photosynthesis withdraws carbon dioxide from the troposphere. Due to the mineralisation (decomposition) of biomass, carbon dioxide is subsequently released again until springtime. Therefore, the year amplitude amounts to around 15 ppm. The concentration level is slightly higher at the measuring stations in low lands, because particularly in winter the mountain stations lie above the so-called mixing layer. Due to the fact that the atmospheric mixture does not occur quickly, slightly higher concentrations are measured in areas with strong emission sources than at background stations. For Schauinsland (Black Forest, Germany), a monthly average "fossil excess" of up to 10 ppm was found (annual average 1.9 ppm), and in Heidelberg of up to 50 ppm (UBA 2000).

CO2 Emissions The carbon dioxide increase in the atmosphere since the middle of the 19th century, which rose from 280 ppm to 381 ppm in 2006, is due to human activities. As shown in Fig. 5.10, since 1950, the earth (sea, land surfaces with vegetation) absorbs an average 40 % of the carbon dioxide which has been emitted by the combustion of fossil fuels, and thus clearly reduces the carbon dioxide increase in the atmosphere (Hansen 2004, see also chapter 2 and 10.2). According to IPCC 2007 the annual fossil fuel carbon dioxide emissions increased from an average of 6.4 (6.0 to 6.8) Gt C per year in the 1990’s, to 7.2 (6.9 to 7.5) Gt C per year in 2000 – 2005). Carbon dioxide due to land use change are estimated to be 1.6 (0.5 to 2.7) Gt C per year over the 1990’s, although these estimates have a large uncertainty (SPM, IPCC 2007).

. Fig. 5.10: Measures of atmospheric CO2 growth rates (B) Increase of the global carbon dioxide emissions in Gt C/year due to the combustion of fossil fuels between 1950 and 2003, their amount which remains in the atmosphere (Airborne Amount), and the amount which is soaked up by the ocean and biosphere (Soaked-Up Amount). (C) The amount of carbon dioxide remaining in the atmosphere and originated in the fossil carbon dioxide emissions between 1950 and 2003, varies strongly from year to year, but on average it amounts to a constant 60 % (Hansen 2004)

Gas emissions of the sea or the soil contribute to the carbon dioxide increase only to a small degree. There are several reasons for it: - The anthropogenically caused emission due to the use of fossil energy – at present around 7.5 billion tons of carbon per year - is higher than its corresponding share in the atmospheric concentration increase (see also chapter 10.2). The values are nearly con- current if the carbon sinks are included (sea and vegetation with around 3 billion t C/a). In the period between 1990 and 2003, the global CO2 emission due to fossil combustion has increased at 20 % (IEA 2005b). - Neither in the oceans nor in the soils a decrease of carbon dioxide was observed.

- Parallel decrease of the C-14/C-12 ratio in the case of atmospheric CO2. Hans Suess, Univ. California, firstly described this so-called Suess Effect at the beginning of the 1950s. This effect occurs because fossil fuels do not contain any C-14. The reason for it is that fossil fuels are much older than 10 half-lives of the carbon isotope C-14.

- Parallel decrease of the C-13/C-12 ratio in the case of atmospheric CO2. This effect is due to the fact that fossil fuels, trees and soil carbon originate from photosynthetically created carbon which contains distinctly less C-13. - Parallel decrease of the oxygen content in the atmosphere which is an unavoidable consequence of the oxidation of carbon to carbon dioxide (= combustion process). Source: Bard 2005, Bousquet 2000, Keeling 1996, McNeil 2003, Takahashi 2002, IPCC 2001

5.1.3 Methane (CH4)

Methane (CH4) is the second most important greenhouse gas. Methane contributes to the greenhouse effect both directly and indirectly, directly because of its absorption bands in the IR range, and indirectly because it is a source of climate-relevant gases like ozone, carbon dioxide, carbon monoxide and water vapour. The global warming potential is 21 times higher than that of carbon dioxide, and it contributes to the greenhouse effect by around 15 %. In the atmosphere, methane is destroyed by many single reaction steps with OH, in the stratosphere also by the reaction with chlorine and oxygen, and on the ground by absorption. Its destruction in the stratosphere leads to an increase of the water vapour concentration and thus to an additional radiative forcing which is taken into account as an indirect effect when calculating the radiative forcing of methane. According to a new study of Shindell 2005, further indirect effects, which are due to the reaction with other atmospheric trace gases like ozone and OH, as well as NOx, CO and the VOCs, nearly double the climate forcing which is estimated to be 0.8-0.9 W/m2. There are still uncertainties concerning its sources and sinks (WDCGG 2005). The average atmospheric lifetime is 12 years. In 2006, Keppler published the results of new measurements according to which also plants are able to produce methane and to emit it into the atmosphere. There is even a distinct in- 58 crease in the methane production in plants at higher temperatures. This explains the high methane concentrations above tropical forests which have been measured with the help of satellites.

Since the middle of the 18th century, the CH4 concentration in the atmosphere has risen by 150 %. From 1000 until 1800, the methane content amounted to nearly constant 700 ppb. In 2005, the average annual concentration amounted to 1774 ppb (in Germany, between 1756 and 1875 ppb (UBA)). The annual concentration fluctuations are highest in the northernmost latitudes and decrease towards the South.

Measurements are shown from ice cores (symbols with different colours for different studies) and atmospheric samples (red lines).

Fig. 5.11: left: Monthly average methane concentration (a) and annual increase rate (b) of the years between 1984 and 2004 (http://gaw.kishou.go.jp/wdcgg.html), right: changes in atmospheric methane concentration over the last 10,000 years (large panels) and since 1750 (inset panels) (SPM, IPCC 2007)

For the period between 1984 and 2004, the global annual increase rate (Fig. 5.11) amounted to an average 7 ppb, for the period between 1984 and 1990, it amounted to 11 ppb/year, between 1991 and 2002 it was distinctly reduced with 5 ppb/year, and 1998 showed a high increase rate, together with a simultaneous extraordinarily high global temperature. The stabilisation of the methane concentrations at the current level would require the reduction of the global anthropogenic methane emissions by 8 %.

Average monthly CH4 concentrations show seasonal fluctuations with high concentrations in winter and low ones in summer. High temperature anomalies lead to an increased methane emission from marshlands and to an augmented assimilation by increased OH radical concentrations. As have proved measurements, the first effect prevails on global scale.

Methane Emissions In contrast to unambiguous concentration measurements, it is extremely difficult to determine the origin of methane. Statements of methane emissions from the cultivation of rice are possibly estimated to be too high and amount to only 30 instead of 88 Mg/year (EPA 2006). The annual increase rates have clearly diminished in the past years. The discussion about its reasons encircles methane reductions in coal mining, gas transports, landfills and rice cultivation. On the other hand, there is a chance that the life span of methane in the atmosphere changes due to variations in the content of atmospheric OH, because OH is the primary methane sink (Hansen 2004). Bousquet 2006 states that since 1999, the anthropogenic 59 methane emissions have increased again but have been compensated by lower emissions from marshlands.

Fig. 5.12: Global breakdown of human-related of methane emissions (283 Tg/year) (EPA 2002) (http://www.epa.gov/methane/intlanalyses.html

Per year, around 500 million tons of CH4 are emitted on a global level. Mankind contributes to it by around 60 – 70 % (TAR (IPCC 2001) stated 598 million t total). Between 1970 and 2000, the global methane emission increased by 33 % (IEA 2005b). IIASA 2006 states 335 million t of anthropogenic CH4 emissions for the year 2000 (see also chapter 10.3). The main anthropogenic share can be attributed to livestock production (28 %) and the cultivation of rice (11 %), mining, oil and gas exploitation (15 %) (Fig. 5.12). Further shares are due to landfills and biomass combustion. Natural sources are marshlands, swamps (tundra) and the tropical rainforest, as well as termites, sea and methane hydrates (Fig. 5.13). The TAR documented a large range in estimates for the global sources in CH4 and no significant improvement have been published since then (IPCC 2007).

Fig. 5.13: Shares of natural sources (marshlands, termites, sea and methane hydrates (190 Tg/year)) of the atmospheric methane concentration (EPA 2002) 60

5.1.4 Nitrous Oxide (N2O) Nitrous oxide is a relatively stable and long-living greenhouse gas with a residence time of 114 years. Being an IR absorbing gas, N2O directly contributes to the greenhouse effect by around 4 % (global warming potential of 310). Due to its long life span, it also reaches the stratosphere where it contributes to the ozone depletion. N2O is mainly removed from the atmosphere by photodissociation which takes place in the stratosphere.

Fig. 5.14: Development of the N2O concentration and radiative forcing in the past ten thousand years (SPM, IPCC 2007)

Since 1750 (270 ppb), the nitrous oxide concentration has risen by around 17 % (Fig. 5.14), the current concentration of 319 ppb has remained unmatched for the past 1000 years. The increase rate temporarily dropped in the years between 1991 and 1993, which is supposedly due to a decreased use of manure, reduced biogenic emissions and bigger stratospheric losses due to volcanically induced circulation fluctuations. The annual increase rate of around 0.8 ppbv is relatively constant in both hemispheres. Since 1978, the increase rates have remained relatively constant (Hansen 2004).

N2O Emissions

The balance of N2O emissions is connected to considerable uncertainties (UBA 2000, IEA 2006). N2O is emitted from natural (approx. 61 %) and anthropogenic sources (approx. 39 %). Above all, these are oceans, soils, the combustion of fossil fuels and biomass, the use of fertilisers and various industrial processes. TAR (IPCC 2001) estimated the following global N2O emissions for the mid 1980s: a total of 14.7 million t (Tg) N/year, of it, 9 Tg N/year are natural sources (grass land, forests, savannahs, sea), and 5.7 Tg N/year are anthropogenic sources (agriculture with 3.5, biomass combustion with 0.5, industry with 1.3 and lifestock production with 0.4). For 2000, EPA states a value of 11.2 Tg N2O for the global emissions (Fig. 5.15) (see also chapter 10.4). For the period between 1970 and 2000, the global anthropogenic N2O emission has increased at 40 % (IEA 2005b).

Human sewage 2%

Fig. 5.15: Global breakdown of anthropogenic N2O emission of 11.2 Tg in 2000. With 76 %, the agricultural (ag) soils have the biggest share (source: EPA 2002, (http://www.epa.gov/methane/intlanalyses.html))

5.1.5 Ozone Ozone is an extremely climate-effective IR-absorbing greenhouse gas which is not directly emitted into the atmosphere from natural or anthropogenic sources. Its contribution to the anthropogenic greenhouse effect is stated to be around 9 %. Ozone is a triatomic oxygen molecule. In the troposphere, ozone has detrimental effects on health, yet in the stratosphere, ozone absorbs the unhealthy UV-B radiation. Ozone (O3) is a trace gas with an average concentration of around 30 ppbv (= 0.03 ppmv) near ground level, and 10 ppmv in the stratosphere. 90 % of the total ozone amount is contained in the stratosphere, and only 10 % in the troposphere (Fig. 5.16).

Fig. 5.16: Schematic representation of the vertical distribution of ozone in the troposphere and stratosphere (WMO 2003)

A part of the tropospheric ozone (around 15 %) is transported from the stratosphere into the troposphere, the rest is produced in the troposphere by chemical reactions. Ozone is produced by photolytic oxidation of carbon dioxide, methane and carbohydrates in the presence of NOx, and has an atmospheric lifetime of hours up to days. The NOx concentration in the atmosphere has a decisive influence on the ozone production (Dameris 2005). This reaction produces the OH radical which is important for the oxidative force of the atmosphere ("self- purification"). 62 TAR (IPCC 2001) states that global ozone emissions amount to 370 Tg (million t). Compared to the pre-industrial value, the ozone concentration has increased by 25 % at least (Lelieveld 2004). Also in the past 30 years, an increase in ozone has been measured in industrial countries, with the exception of Canada. Due to the strong seasonal and regional fluctuations, it is difficult to establish a uniform long-term ozone trend for the Northern hemisphere. According to DWD, the annual values in the Northern hemisphere for the period between 1975 and 1999 have increased from 31 to 40 ppb (UBA 2003). In contrast thereto, a significant decrease has taken place in the stratosphere. At the Hohenpeißenberg (Germany), an almost 16 % decrease in the stratosphere has been measured since 1967 (since 1992, a slight increase), and in the troposphere an increase of around 30 % (however, a slight decrease since around 1990) (Fricke 2001). At all measurement stations in Germany, the ozone at ground level has increased by approx. 20 % for the period between 1984 and 2004. Since 1994, there has been practically no increase, with the exception of the extreme summer of 2003 (Fig. 5.17).

Fig. 5.17: Development of the average annual ozone values in Germany for the period 1984 – 2004 at all measurement stations in µg/m3 (Umweltdaten 2006, UBA (http://www.env-it.de/umweltdaten/public/theme.do?nodeIdent=2373))

The different international treaties for the reduction of ozone-depleting substances, drawn up between 1987 (Montreal) and 1999 (Beijing), have resulted in the fact that in the meantime it is possible to measure the drop in CFCs. With this, it may be expected that the ozone depletion in the stratosphere will be stopped in the long term, and that the ozone layer will recover by 2050.

5.1.6 F-Gases and Halogenated Hydrocarbons (FC, CFC, HFC) F-gases are the fluorinated greenhouse gases listed in the Kyoto Protocol which comprise the partly-fluorinated hydrocarbons (HFC, HCFC), the substance class of completely or per- fluorinated hydrocarbons (FC, PFC) and sulphur hexafluoride (SF6) (see chapter 5.1.8). At the beginning of the 1990s, the chlorine-free substitutes - HFC and FC - were introduced in order to replace the ozone-depleting CFCs. The HFC and FC are carbohydrates with fluorine (F), and they "only" play a role in the greenhouse effect. Halocarbons is a general term for carbonaceous compounds which contain halogens (Cl, Br, F, J) and partly hydrogen. Halogenated hydrocarbons (in particular CFC, HCFC) is a general term for carbon compounds which contain one or several halogens, like fluorine, chlorine, 63 bromine, iodine. CFCs are carbohydrates, where hydrogen atoms are substituted by the halogens chlorine or fluorine, respectively. HCFCs are partly halogenated CFCs in which the hydrogen atoms are only partly substituted by chlorine and fluorine atoms. Their ozone- depleting potential is essentially reduced compared to the CFCs, and their global warming potential is also strongly reduced compared to that of the CFCs. Notwithstanding their low concentration in the ppt range, they have two effects: In the stratosphere, they deplete the ozone layer (Ozone Depleting Substances, ODS), and in the troposphere they contribute to the warming. They are the only greenhouse gases of anthropogenic sources. In the past decades, they were used by industry for different purposes like propellants in aerosol dispensers, blowing agent for foams, cooling agent in fridges and air conditioning systems, and as detergents for textiles and in electric components, because they are non-combustible and non-toxic. Because of their ozone-depleting properties in the stratosphere, the use of halogenated hydrocarbons was increasingly restricted by several international agreements (Montreal Protocol 1987, London 1990, Copenhagen 1993, Beijing 1997). Because of the fact that the CFCs are chemically inert - they do not react with other substances -, they remain in the atmosphere for very long periods of time (some for more than 1,000 years). Compared to carbon dioxide, they additionally have an extremely high global warming potential due to their strong absorption in the infrared band which amounts to 6,300 and 10,200 within the first 20 years. With an estimated percentage of 11 % in the anthropogenic greenhouse effect, they are the third most important greenhouse gas after CO2 and CH4. In addition to this warming effect, they also have an indirect cooling effect which is due to the depletion of the ozone layer in the stratosphere. The depletion of the ozone layer in the stratosphere leads to a clear cooling which also influences the troposphere (see chapter 6.3). In a new IPCC 2005 Special Report, the indirect radiative forcing is estimated to be -0.15 ± 0.10 W/m2. The value of this negative radiative forcing is most likely smaller than the positive direct radiative forcing which amounts to 0.32 ± 0.03 W/m2.

Fig. 5.18: Trend of the 13 trace gases as settled in the Montreal Protocol for the period between 1992 and 2003. The increase rates of the radiative forcing in this period have dropped to nearly 0 and currently amount to 0.3 W/m2 (Han- sen u. Sato 2004)

Since the beginning of the 1940s, and until the 1990s, an increase of the CFCs in the atmosphere was measured. Then, the increase of the completely halogenated CFCs started to drop or slow down (Fig. 5.18). The less critical substitution substances (HFCs, partly halogenated CFCs with a lower global warming potential) are still increasing, albeit at a slower rate. On a global scale, the use of CFCs has dropped by over 90 %. In Germany, practically 64 no CFCs are used anymore, but being a replacement for the CFCs, the HFC share in blowing agents for foams and cooling agents increased in the period between 1995 and 2003 from 2591 t to 6540 t (this corresponds to 8.5 million t CO2 equivalents). In contrast to this, the HFC emissions dropped for the same period by 366 t to 121 t (0.86 million t CO2 equivalents) which is due to emission reducing measures in the aluminium production (Schwarz 2004). Due to their relatively strong infrared absorption and their long atmospheric lifetime of up to 14,000 years, the HFCs and FCs have a high global warming potential. For the most important fluorinated gases, it fluctuates between 140 and 7,000 for the HFCs, and between 6,000 and 9,000 for the FC (Schwarz 2004). Their share in the greenhouse gas emissions (CO2eq) amounts to around 1 % in Germany.

5.1.7 Sulphur Hexafluoride (SF6)

Sulphur hexafluoride is chemically extremely stable, the average atmospheric life span is several 1000 years. Additionally, it has a very high global warming potential of 23,900. Sul- phur hexafluoride has practically no natural source in the atmosphere (Schwarz 2004).

Emissions are exclusively due to industrial production. SF6 is mainly used as a spark extinguishing gas in high-voltage switchboards, as tyre fillings, as isolating gas in thermal protection windows and in the aluminium production. Due to leakages, small amounts escape into the atmosphere. The SF6 concentration in the atmosphere amounted to 5.4 ppt in 2004 and has been increasing at 0.2 ppt per year on a global scale for some years (http://www.noaanews.noaa.gov/stories2005/s2512.htm). In 2000, around 6,000 t were globally emitted. In Germany, the SF6 emissions were reduced from 276 to 187 t in the period between 1995 and 2004 (see also chapter 10.9). At 0.4 %, their percentage in the greenhouse gas emissions is relatively low, even with regard to their high global warming potential.

5.1.8 Indirect, Ozone-Forming Greenhouse Gases In the following, substances are listed the emissions of which influence the atmospheric ozone and methane budget (indirect greenhouse gases: NOx, NMVOC, CO). The chemical interactions in the atmosphere are very complex. As an example, the NOx decrease alone has different effects on the radiation budget than the decrease of all indirect greenhouse gases (Naik 2005).

5.1.8.1 Nitrogen Oxides (NOx) without Nitrous Oxide

Nitrogen oxides (NOx, especially NO and NO2) are no greenhouse gases, but they destroy the OH radical, which influences the concentration of methane, carbon monoxide and CFCs in the atmosphere. Additionally, NOx contributes to the formation of ozone in the troposphere by photochemical processes. NOx is removed from the atmosphere by conversion into nitric acid (HNO3) and wet deposition. NOx has a short life span of up to one day. During periods of severe air pollution and thunderstorms, a local radiative forcing of NO2 was observed (Solo- mon 1999), which may lead to an additional warming. According to Velders 2001, its contribution to the radiative forcing for Western Europe and parts of North America is estimated to be 0.1-0.15 W/m2, when the sky is clear. At a global level of 0.005 W/m², the forcing is negligible. There are big differences in the distribution of atmospheric NOx concentrations around the globe (0 – 40 ppb). With the help of satellite data, the local and temporal trend was researched in the framework of the GOME research project. Since 1996, satellite measurements indicate a strong increase in the atmospheric NOx concentrations above the industrialised regions of China, a clear decrease above Europe and varying trends above different parts of the USA (Richter 2005).

NOx Emissions

Sources for the NOx emissions are the combustion of fossil fuels and biomass, lightnings and soils. After evaluating the data from measuring flights carried out within the framework of an EU project in 2004, the share of nitrogen oxides from thunderstorms was estimated to be 65 less than 10 million t/year. Thus, the main part of natural nitrogen oxide originates in thunderstorms. Due to the high energy of lightnings, oxygen and nitrogen in the air combine to form nitrogen oxides. Anthropogenic NOx emissions produced during the energy conversion originate mainly from the combustion of fossil fuels, in particular by street and air traffic and firings of any kind. Further important emissions emanate from nitric acid installations (combustion of ammonia) and from the production and use of manure containing nitrogen. In TAR (IPCC 2001), the following emission estimates were taken as a basis: Total: 41 million t (Tg) N/year, of which 21 from the combustion of fossil fuels, 0.6 from air traffic, 6.4 from the combustion of biomass, 5.5 from soils, 7.0 from lightnings and <0.5 from the stratosphere. According to IIASA 2006, the anthropogenic NO2 emissions amounted to 81 million t in 2000.

The total German part of NOx amounted to around 6 % of the worldwide anthropogenic NOx emissions in 1990. In the period between 1990 and 2004, the emissions nearly halved and dropped from 2.9 million t to 1.6 million t (Fig. 5.5) (see also chapter 10.6).

5.1.8.2 Organic Compounds without Methane (NMVOC)1) VOC are volatile compounds like toluene or benzene. In the presence of nitrogen oxides and sunlight in the atmosphere, they produce the greenhouse gas ozone. Because of their reaction with OH radicals, they additionally inhibit the reduction of direct greenhouse gases like methane and thus reduce the self-purifying capacity of the atmosphere. Certain VOCs form aerosol particles which disperse or absorb radiation and influence the cloud formation (Plaß- Dülmer, 2005).

NMVOC Emissions NMVOC are carbon compounds (without methane) which are formed particularly during incomplete combustion processes. They proceed from the motor vehicle traffic, industry, heating systems, chemical production processes (refineries, chemical plants) and escape during the evaporation of solvents. They are naturally emitted in big quantities (2/3 of the global emissions) by deciduous and coniferous trees in the form of terpenes and isoprenes. In TAR (IPCC 2001), the following estimates of the global emissions were taken as a basis: In total 571million t (Tg) VOC/year, of them 161 emanating from fossil combustion, 33 from biomass combustion, 377 from the vegetation (isoprenes, terpenes, acetone). Anthropogenic and biogenic sources in Central Europe contribute nearly equally to the VOC presence in the lower troposphere (Plaß-Dülmer 2005). In Germany, NMVOC emissions were reduced by around 65 % from 3.6 Mio t (Gg) to 1.2 Mio. t for the period between 1990 and 2004 (Fig. 5.5) (see also chapter 10.7). This is mainly due to the use of catalytic converters in vehicles and to the reduction of solvents in paints, varnishes and adhesives (UBA 2005).

5.1.8.3 Carbon Monoxide (CO) Carbon monoxide is the most important indirect greenhouse gas, because it contributes to the formation of ozone in the troposphere. The main sink is the oxidation of CO with the OH radical to form CO2. Thus, the OH radical is not available anymore for the reduction of greenhouse gases like methane. The average residence time in the atmosphere amounts to 3 to 4 months. Due to its described properties, CO reduces the self-purifying capacity of the atmosphere and thus contributes indirectly to the greenhouse effect. The average global concentration in the atmosphere amounted to 98 ppm in 2002 (Fig. 5.19). From the 1950s until the middle of the 1980s, an annual increase of the atmospheric CO content from 0.3 to 1 % was observed. Then it stagnated more or less with great regional differences. At present, experts are discussing the various reasons for it: a reduction of the biomass combustion, increase of the concentration of OH radicals due to the thinning ozone layer and the increase in UV radiation linked with it, and the reduction of anthropogenic emissions due to effective emission-reducing technologies (Gilge 2001).

1) NMVOC = Non Methane Volatile Organic Compounds 66

Fig. 5.19: Global mean CO concentration (98 ppm) and increase rate 1992 – 2002 (WDCGG 2005)

CO Emissions CO derives from natural as well as anthropogenic sources. On a global scale, the oxidation of methane and the combustion of biomass are important direct sources. The estimates of the global CO budget (in Tg CO/year) according to IPCC 2001 vary greatly, depending on the author. TAR took the following values as a basis: a total of 2.8 million t (Tg) CO/year, of which 1.2 million t (Tg) CO/year due to oxidation in the atmosphere (methane (800 Tg), iso- prene (270), NMHC (140), acetone (20)), and direct emissions of 1.55 million t (Tg) CO/year, of which vegetation (150), sea (50), biomass combustion (700), the combustion of fossil fuels (650). For 2000, IIASA 2006 states 470 million t (Tg) CO emissions due to the combustion of fossil fuels. The use of fossil fuels (traffic, industry, heating) - particularly in the case of incomplete combustion - is an equally important source in the Northern hemisphere. In Germany, the carbon monoxide emissions were reduced by 70 %, from 12.1 million t to 3.7 million t (Tg) during the period between 1990 and 2004 (Fig. 5.5) (see also chapter 10.8).

5.2 Sulphur Dioxide (SO2) Being the precursory substance for the sulphate aerosols, sulphur dioxide is an important tropospheric trace gas. Sulphate aerosols are produced by the oxidation of SO2 in the course of a photochemical gas-particle conversion. Since the sulphate aerosol belongs to the "dispersing aerosols", it counteracts the greenhouse effect and thus has a considerable effect on the development of the climate.

Sources of SO2 come above all from the combustion of fossil fuels (72 %) and biomass (2 %), to a smaller extent from volcanoes (9 %), and the oxidation of dimethylsulphide (DMS) from the sea (19 %) (Koch 2007). In the Northern hemisphere (Fig. 5.20), SO2 is mainly emitted from power plants, industrial furnaces, domestic fuelling and traffic. After the discussion about the forest damages in the 1980s ("acid rain"), the emissions were drastically reduced - in Germany by nearly 90 % from 5.3 million t to 0.56 million t (NIR 2006) (see also chapter 10.10). In most of the industrialised countries, the immissions have correspondingly dropped by a considerable amount, too. Since 2001, at some of the measurement stations of ‘pure air’ in Germany, there has been a slight increase, although at a very low level and possibly due to long-distance transport (Kaminski 2005). Due to the advancing industrialisation in the Asian threshold countries, significant increases have been found there. The net result of these regional reductions and increases leads to uncertainty in whether the global SO2 has increased or decreased since the 1980s (Boucher 2002, IPCC 2007). According to Koch 2007 not all (1/3 to 1/2) of SO2 emission from Southeast Asia and Europe produce sulfate 67 because of the limited amount of oxidants in the atmosphere to convert the emitted SO2 to sulfate. North South Global Range Koch 2007 Hem. Hem. IPCC 2001 Sulphur dioxide Total 75.54 12.003 87.54 84 Fossil fuels and industry 68 8 76 66.8 - 100 73 Air traffic (1992) 0.04 0.003 0.04 0.03 – 1.0 Biomass combustion 1.2 1.0 2.2 1 - 6 2 Volcanoes 6.3 3.0 9.3 6 - 20 9

DMS and H2S Total 12.6 13.4 26 29 Marine biosphere 12 13 25 13 - 36 Terrestrial biosphere 0.6 0.4 1.0 0.4 -5.6

Fig. 5.20: Sulphur dioxide, DMS and H2S emissions in Tg S (million t) per year, listed for the Northern and Southern hemisphere, mid 1980s, IPCC 2001, recent values (right) are in the same range (Koch 2007) 5.3 Aerosols In the past years, the aerosols have become increasingly important in climate discussions (Feichter 2004). While 20 years ago, practically only the influence of the greenhouse gases on the climate was being discussed, in the second IPCC report in 1995 the sulphate aerosols were brought into the picture, and these were supposed to be the reason for the much lower rise in the temperature of the atmosphere than had been expected according to the theory.

North. South. Global Range AeroCom Hemisph. Hemisph. 2006 Organic material (0-2 μm) Biomass combustion 28.3 26.0 54.3 45 - 80 9.1 wildfire 34.7 Fossil fuels 28.4 0.4 28.8 10 - 30 3.2 Biogenic (>1 μm) 56 0 - 90 Black carbon (0-2 μm) Fossil fuels 6.5 0.1 6.6 6 - 8 3.0 Biomass combustion 2.9 2.7 5.6 5 - 9 1.6 wildfire 3.1 Air traffic 0.005 0.0004 0.006 Industrial dusts 100 Sea salt 1440 190 3,340 1,000–6,000 7,925 Mineral dust 1,800 350 2,150 1,000-3,000 1,678

Fig. 5.21: Aerosol emissions (primary particles) in Tg/ listed for the Northern and Southern hemisphere, estimates with indication of the ranges as stated in literature for the mid 1980s, according to IPCC 2001and new values from Aero- Com (Dentener 2006) Gradually, a whole range of further natural and anthropogenic aerosols were discovered which could influence the climate directly or indirectly (Fig. 5.21). The current knowledge and uncertainties of emissions of aerosols are still very high (IPCC 2007). In comparison to TAR the values for fossil emissions of black carbon and organic matter were strongly reduced (Dentener 2006, AeroCom) (Fig. 5.21 right) The biggest fraction of the atmospheric aerosols are the natural primary particles from wind- driven sources (Feichter 2004), like sea salt and mineral dust (Fig. 5.21 - 5.22). According to 68 recent statements, of the 5 billion t of natural mineral aerosols, 1.5 billion t are desert dust, of which 60 % come from the Sahara (http://www.dlr.de/ipa).

Fig. 5.22: Sahara dust above Northwest Africa and the Atlantic on the 26.02.2000, observed by the SeaWiFS Satellite (NASA) (http://www.tropos.de/PHYSIK/fernerkundung/projekte/samum.html#samum1). Up to 1.5 billion t of desert dust are annually transported into the troposphere, 60 % of it comes from the Sahara

Today, the satellite observation of the global dissipation of anthropogenic aerosols works very well (Fig. 5.23).

Fig. 5.23: Global distribution of anthropogenic aerosols. Measurement of the optical thickness by satellite images; a, c, e: mainly urban areas, b, d: areas with biomass combustion (source: Solomon 2005)

The regional effects aerosols have on the climate were researched in extensive international research programmes, like the Indoex Experiment in the Indian Ocean (Ramanathan 2001, 2005).

Aerosols are emitted into the atmosphere either directly (primary aerosols), or they are produced in chemical processes from precursory substances (secondary aerosols) (Fig. 5.24). Aerosols are small particles which are floating in the air, have a diameter of less than 10 µm and can reach the atmosphere due to natural processes like wind, volcanic eruptions or the combustion of fossil fuels or biomass. The aerosols change in the atmosphere, cluster (co- 69 agulate), are chemically conversed and form condensation nuclei of cloud droplets and ice crystals. The atmospheric residence time is short and amounts to hours and days. Then they are washed out or deposited in a dry state. If these particles reach the stratosphere by means of aircraft exhaust fumes or volcanic eruptions, their life span is much longer with periods between 1 and 3 years (Kasang, HBS 2005). These quick changes of the aerosols make research of them extremely complicated.

Fig. 5.24: direct and indirect Aerosols: important processes of their production, conversion and removal from the atmosphere dust aerosol: primary aerosol, sulphate aerosol: secondary aerosol, sulphur dioxide: precursor substance (source: Kasang, HBS 2005)

In principle, a difference is made between the direct and indirect influence of aerosols on the radiation budget and the climate. The direct effect derives from the reflection of incoming solar irradiance by the aerosols (in particular the sulphate particles) into space and the cooling effect connected to it (Fig. 5.25).

Fig. 5.25: The direct effect of aerosols due to reflection and absorption (Kasang, HBS 2005) 70

Boucher 2002 calculated the direct radiative effect of sulphate aerosols for 1990 and has found a negative radiative forcing of up to 3 W/m2 for the industrial regions in Central Europe, China and the USA (Fig. 5.26). In most regions (North America and Europe) cooling from sulphate aerosols counteract some of the greenhouse warming (Stott 2003).

Fig. 5.26: The direct radiative effect of sulphate aerosols for 1990, compared to 1850 (Kasang, HBS 2005, altered according to Boucher 2002)

Also black carbon (soot) particles and some other aerosols have a cooling effect because they absorb the solar radiation, thus heating up the surrounding air but cooling down the near-surface air layers. According to model calculations by Liao 2004, the change in the radiation balance at the upper limit of the atmosphere is due to the direct effect of all the aerosols and amounts to -0.72 W/m2, for the ground it amounts to -4.04 W/m2. The big difference is mainly due to the varying radiative effects of the soot aerosols. Dust aerosols may have a similar effect. According to Stier 2005, the results of recent model calculations with the aerosol climate model ECHAM5-HAM in general correspond quite well to the observed global aerosol system. The model contained the most important aerosol components like sulphate, soot, organic particles, sea salt and mineral dust. Bellouin 2005 determined the direct radiative forcing of aerosols for 2002 by means of NASA satellite measurements. The evaluation of the spectrometers in a clear sky showed a mean annual radiative forcing of -1.9 W/m2, with a standard deviation of ± 0.3 W/m2. The global average value for all weather situations amounts to 0.8 ± 0.1 W/m2, and with this it lies at the upper end of the range (0.2 - 1.0 W/m2), as has been indicated in the IPCC Report 2001. Us- ing other procedures, Chung 2005 calculated a value of -0.35, and Yu 2005 of - 0.5 W/m2. This shows the great uncertainties that still exist concerning the calculation of the radiative forcing of aerosols. Another source of uncertainty is the still insufficient knowledge of the tridimensional dispersion of each aerosol type in the atmosphere, and their development. According to IPCC 2007 the total direct anthropogenic forcing is -0.7 (-0.9 to –0.1) W/m2. The indirect effect of the aerosols (Fig. 5.27) derives from their influence on the cloud formation and precipitation (Lohmann 2005). In particular, they form condensation nuclei for the formation of cloud droplets and ice crystals (effect: cooling down, partly warming). Addition- ally, the droplet size is reduced if the number of condensation nuclei is higher, which leads to 71 a reduction of precipitation and extends the life span of clouds. In addition to this, there is a semi-direct effect due to dissolving clouds which is a result of the heating up of the absorbing soot particles. This leads to a higher permeability of the atmosphere for the solar radiation (temperature rise). As far as these effects are concerned, there are still considerable uncertainties. Therefore, the statements of their radiative forcing vary on a large scale. The cloud dissipation due to soot particles was observed e.g. above the Indian Ocean and during forest fires in the Amazonas region (Cook 2004, Graf 2004, Koren 2004). There are still discussions about the extent of the semi-direct effect. Krüger and Grassl 2002, 2004 were able to prove the influence of the indirect aerosol effect in Europe and China.

Black carbon (BC) deposition clearly affects snow and ice. BC absorbs the solar radiation and is heated up at the same time, the reflection of the - originally - bright surfaces decreases. The effect ablates glaciers and snow at a quicker rate. Hansen 2004 states that the "soot effect" on the albedo of the snow could account for a quarter of the global warming. According to Hansen 2004, this change in the radiative forcing has not been considered sufficiently in the existing evaluation of the IPCC. Statements made in literature on the indirect effect of aerosols vary extremely between -1.9 and -0.5 W/m2 (Quaas 2006). Quaas evaluated aerosol measurements by means of spectral radiometers of satellite data (2000-2005) and used these for the parameterisation of the models (ECHAM4 and LMDZ). Therefore, it was possible to considerably limit the range of the indirect aerosol effect to -0.5 and -0.3 W/m2. According to IPCC 2007 the indirect cloud albedo forcing is – 0.7 (-1.8 to -0.3) W/m2.

Fig. 5.27: Indirect and semi-indirect effect of aerosols and their influence on the cloud formation (HBS 2005) By means of model calculations, e.g. by the Hamburg Max-Planck-Institut of Meteorology (MPI-M), attempts have been made to determine the global climate effect. According to them, in the period between 1860 and 1985, the aerosols are said to have caused an average global cooling of about 0.9 °C. Fig. 5.28 shows the calculated regional dispersion for the mid 1980s, compared to the pre-industrial value. The cooling is strongest in the Northern hemisphere. The clear effects in the Polar regions and Siberia are caused by the snow- albedo effect (Feichter 2004). According to Feichter 2004, at all geographic latitudes on the continents, the aerosol effect has clearly been surpassed by the warming effect due to anthropogenic greenhouse gases in the last 150 years. The role of the aerosols with an extremely high regional radiative forcing of -20 ± 4 W/m2 was also proven in the international 72 INDOEX experiment (Ramanathan 2001, 2005). TAR did not include any assessment of the semi-direct effect.

Fig. 5.28: Changes of the average temperature near ground level in the mid 1980s due to anthropogenic aerosols, compared to the pre-industrial value (direct and indirect effect), according to a model calculation of the Hamburg MPI (altered according to Feichter 2004, source: HBS, Kasang 2005)

Another phenomenon was the decrease of solar irradiance at ground level discovered some years ago ("global dimming“) in the period between the 1960s and 1980s of a global average value of around 7 W/m2 or 4 % - 6 %. The reasons are considered to be, to a smaller extent, greenhouse gases and the connected increase of water vapour concentration, and in particular the increase of aerosols and the linked increase of the cloudiness (Stanhill 2001). Mean- while, in some parts of the world, like in Europe and USA, an increase of the solar irradiance has been measured (global brightening) since the 1990s. Whereas the decrease of the solar irradiance could have counteracted the greenhouse effect, it could have enhanced the greenhouse signal after 1990 (Wild 2005). According to model calculations by Andreae (2005), the climate warming in the 21st century could be much stronger if the emission of anthropogenic aerosols came to an end.

5.4 Changes in the Use of Land Changes in the use of land are caused by deforestation, reforestation, irrigation and urbanisation. Nearly one third of the continental surface is covered by forests (Fig. 5.29). The net loss of forest areas due to clearings and reforestation is estimated to be 7.9 million ha/year (0.2 %) for the period between 2000 and 2005 (FRA 2005). The most extensive clearings take place in Africa and Central and South America with a loss ratio of more than ½ %/year. DeFries 2002 states the annual average net carbon circulation on account of the tropical deforestation to be between 0.6 - 0.9 billion t/year for the 1980s and 1990s, figures based on satellite measurements. This is clearly less than the FRA 2005 (Forest Resource Assess- ment) estimates with 1.9 (0.6-2.5) billion t per year. In recent years, discussion has focussed on the question whether changes in the use of land, as we have experienced it for thousands of years, could have influenced our climate (Pielke 2005, Liess 2004). The large-scale clearing or burning of forests is common practice. Ac- cording to estimations, this has an effect on approximately between a 1/3 and up to half of our terrestrial surface (Claussen 2003). The land use changes the structure of the terrestrial surface, because agricultural surfaces are often brighter than forest areas, and they also show a different evaporative behaviour. According to Claussen 2003, a slight cooling will be 73 probable on a global average which is basically due to the increasing reflective power of solar radiation. This is confirmed by model calculations of Bauer 2003. The use of land does not only change the structure of the terrestrial surface but contributes to the CO2 and soot emission by forest burning. Changes in the use of land may influence manifold climate-relevant factors like emissions of dust, soot and greenhouse gases, changes in the albedo and radiative balance at ground level, as well as changes in the evaporative behaviour. Therefore, they are not yet included in the climate models in detail (BASC 2005). On a global scale, the reduction of the evaporation due to the deforestation is more or less counterbalanced by an increase in the evaporation due to the irrigation of the agricultural areas. Yet, regional differences have a considerable effect on the climate (Gordon 2005).

Fig. 5.29: Coverage by forests in 2000; nearly 1/3 of the continental surface (dark green = dense forests, medium green = open forests, light green = bushland) (http://www.grida.no/geo/geo3/english/fig91.htm)

Model calculations permit the reconstruction of the large-scale effects of the deforestation in the Mediterranean and the Amazonas. An extreme consequence is the emerging of desert landscapes in the Mediterranean, and of steppes in the Amazonas region (Liess 2004). Fed- dema 2005 also shows that model calculations which consider changes in the use of land, like deforestation and the extension of agriculture, lead to considerable regional climate changes. Due to this, the results of the calculations for the TAR (IPCC 2001) are regionally even reversed – cooling instead of warming or vice versa in certain regions. The IPCC report 2001 considers the influence of changes in the use of land on the carbon dioxide and methane emissions, as well as the mean global albedo change on the model calculations (Pielke 2005), but it does not consider regional changes in temperature and precipitation. Up to now, according to Myrhe (2005), there has only been little research in the changes of the climate forcing due to future changes in the use of land. Therefore, BASC 2005 proposes to take into account future changes in the use of land, considering them to be an additional climate forcing, and to include them in the models in order to get more realistic model results.

6 Climate Observation Since about 1850, the atmospheric pressure and the temperature have been measured for great parts of the earth surface. The number of measurement stations has constantly increased, and now they also include the sea surface with ships and buoys. Since the beginning of the satellite measurements, the data flux has dramatically increased. Measurement series of long periods gathered in a global interlocking measurement system of meteorological, hydrologic and oceanographic services are at the disposal of any interested person (Fig. 6.1).

Fig. 6.1: Development of the gathering of meteorological data since the beginning of the instrument ( Brönnimann 2005)

Satellite climatology has experienced a dramatic rise. In 1959, the first satellite took off with a radiometer on board. Meanwhile, around 20,000 satellites are launched in different orbits around the earth. At present, 3,000 commercial satellites orbit still the earth. Polar orbiting weather satellites are orbiting at an altitude of approx. 850 km, but today, also numerous geostationary satellites orbit the earth at an approx. altitude of 36,000 km. On a regular basis, they map every spot on the earth. Satellites observe the terrestrial radiation field by means of high-resolution sensors which analyse the electromagnetic spectrum. They measure the radiation which is absorbed, reflected or emitted by the earth and atmosphere. With constantly increasing exactitude, they also measure precipitation, aerosols, humidity, solar constant, temperature near ground level and in the atmosphere, ozone column, air composition, cloudiness, snow and ice coverage, and the emitted and reflected solar radiation. Additionally, it is possible to measure the global dispersion and transport of trace gases and aerosols with increasing exactitude. Due to satellite observations, a number of basic climate properties, but also indications of climate trends were found in the last decades. Meanwhile, satellite data is also used for checking results of climate models (Schumann 2003). Today, the evaluation of satellite data is one of the most important facilities for weather forecasts, environment monitoring and climate research (Brönnimann 2004/05, 2005).

6.1 Temperature Trend Near Ground Level The average global temperature is calculated in a complicated statistical procedure (Brohan 2006). Homogenised, quality-controlled monthly average data from around 4,394 continental stations and from ships and buoys on the sea are evaluated. The data are 75 interpolated to a regular grid of the terrestrial surface, with indication of uncertainty ranges and error limits. The results of the three evaluation groups in the USA (NASA, NOAA) and Great Britain (Hadley Centre) vary only slightly.

6.1.1 Average Global Temperature Trends Since the beginning of industrialisation - mid 19th century -, the average temperature of the Earth has risen by about approx. 0.8 °C (Hansen 2006). The main increase occurred between 1910 and 1945, and since 1975 it has continued to today (Fig. 6.2).

Fig. 6.2: Temperature difference from 1850 to 20056in °C (zero point around 1900); the average global temperature increase amounted to 0.8°C (evaluation Hadley Centre/GB, Brohan et al. 2006, Jones 1999/2005) (http://www.metoffice.gov.uk/research/hadleycentre/CR_data/Monthly/Hadplot_globe.gif)

According to evaluations of the WMO, 2005 was the second warmest year since 1861, the warmest year which showed an anomaly of 0.63° C was in 1998. Eleven of the last twelve years (1995 – 2006) rank among the 12 warmest years in the instrumental record of global surface temperature (since 1850) (SPM, IPCC 2007). The anomalies were more pronounced on the continental surfaces than on the sea surface. The linear trend in the 20th century was 0.7 °C and rose to 0.8 °C in 2005. In the past 30 years, it has risen by 0.2 °C per decade (Hansen 2006). Schönwiese 2003 also states a clearly enhanced trend, in particular for the last decades. On the other hand, the warming trend in the Northern hemisphere was interrupted between 1945 and 1975, but after 1975, it showed a strongly increasing trend, similar to the period between 1910 and 1940. In the Southern hemisphere, it continued uninterrupted for the complete period (Fig. 6.3). There are big regional and seasonal differences in the observed climate trends. The period 1891 – 1990 experienced a global warming, but at the same time it is linked to regional cooling, e.g. above the North Atlantic and Central Africa (Fig. 6.9) (Schön- wiese 2003). 76 Next to the increase of the ground-level temperature, double the increase of night temperatures have been observed since 1950. The global average sea surface temperature increased at 0.6 °C in the 20th century, but there were big regional differences.

Fig. 6.3: Temperature trends between 1880 and 2005, separate for the Northern and Southern hemisphere. The increase on the Southern hemisphere has been much less pronounced in the last years (Sato, Hansen 2006, http://data.giss.nasa.gov/gistemp/graphs/)

Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations. This is an advance (SPM, IPCC 2007) since the TAR’s conclusion from ‘likely’ to ‘very likely’. Discernible human influences now extend to other aspects of climate, including ocean warming, continental-average temperatures, temperature extremes and wind patterns (SPM, IPCC 2007). According to Delworth 2000, the warming at the beginning of the 20th century could have been caused by a combination of the anthropogenically induced radiative forcing and an extremely long-lasting variability of the coupled atmosphere/ocean system over the period of several decades.

6.1.2 Warming Trends of the Land Surface Temperature from Satellite Data By means of NASA/NOAA satellite data, Jin 2004 evaluated the land surface temperature for the years from 1981 to 1998. This showed an increased temperature rise of 0.43 °C per decade than was found in air temperature measurements conducted at 2 m height (0.34 °C/decade). But, one problem is the snow covering because it is not possible to carry out measurements underneath it. This means that only approx. 65 % of the terrestrial surface can be taken into account. Also by means of satellite observations, an increase of vegetation activity was found in the boreal zone of the earth (taiga forests and tundra) (Lucht 2002, Myneni 2005, Jia 2003). Meanwhile, springtime starts there 1 week earlier than 20 years ago. The increased growth of the vegetation was clearly caused by higher temperatures which for the Northern countries amount to 0.4 °C per decade.

77 6.1.3 The Past 420,000 Years - Climate History The evaluations of ice cores inform us about the climate history of the past 420,000 years or, in the light of recent evaluations, even the past 650,000 years. The period 100,000 years ago, which was caused by fluctuations in the eccentricity of the earth's orbit (elliptically formed) (see chapter 4.1), is clearly reflected in the temperature variations (Fig.6.4).

Fig. 6.4: Reconstruction of the atmospheric CO2 and CH4 content and temperature variations from Antarctic ice cores of the past 420,000 years (Petit 1999), supplemented by data from the last century until 2004. The zero point of the temperature is the average value for the period between 1880 and 1899 (Hansen 2005)

Recent evaluations of ice cores in the Antarctic within the EPICA Project, and which date back 650,000 years, also show that lower greenhouse gas concentrations were linked to lower temperatures (Siegenthaler 2005). The evaluation of the data from ice cores shows temperature variations of around 10 °C, which were most probably triggered by changes in the earth's orbit. Due to the climate change caused by this, the development of methane and carbon dioxide concentrations widely coincided with the temperature changes. Hansen 2005d, f states that now it is man who changes the trace gas concentrations in the atmosphere and the terrestrial surface and thus increases the earth's temperature (Fig. 6.4).

78 6.1.4 The Past 10,000 Years - Climate History Since the last Ice Age 10,000 years ago, the climate has been considered to be relatively stable with temperature variations of about ± 1 °C. The average temperature of the Ice Age lay at about 5 - 6 °C under the today's value (Fig. 6.5).

Fig. 6.5: Climate trends in the Holocene since the end of the last Ice Age 10,000 years ago (Kasang, HBS 2005 according to Schönwiese)

6.1.5 The Past 1000 Years - The Hockey-Stick Discussion After a publication by Mann 1998, an intensive discussion started about the determination of the average global temperature for times before instrumental measurements were made, because it showed the so-called hockey stick graph which represents the temperature trend of the past 1,000 years (Fig. 6.6). The temperature determination by means of so-called proxy data is a generally accepted method. As far as historical sources are concerned, a difference is made between direct and indirect climate data. Direct data are: weather logs, cloud observations, water marks etc... Indirect statements reflect climate impacts from which the weather conditions may be concluded (e.g. penology, which is the actual state of the vegetation, harvest dates, grain prices, supplicatory processions, gliding flight times above the Atlantic etc.) (Düwel-Hösselbarth 2002, Glaser 2001). During the conversion of this data into usable climate parameters, problems may arise e.g. if a stationary condition is assumed. As an example, it is postulated that the statistical relationship between the date of the grape harvest and the climate has not changed within the course of time. Additionally, extreme events are often overestimated in the chronicles. Criteria like "for ages" or similar are nearly impossible to quantify. Neverthe- less, historic sources may contribute important and precise information to climate history. In terms of time and location, they are very detailed, and they are abundantly existent for Europe, but also e.g. for China. 79

Fig. 6.6: Variation of the average terrestrial surface temperature for the last thousand years. Blue graph: Temperature fluctuations per year. Grey graph: Uncertainties of the annual data. Black graph: 40 year smoothed graph. The uncertainty of the data increases from the right to the left side (Mann 1998)

In addition to historical sources, natural archives also exist which strongly depend on the climate and store the relevant information in highly resolved intervals. Examples are: Tree rings, corals, sediments and ice cores. Used parameters are e.g. ring growth, ice accumulation, ratios of stable isotopes, frequency of certain indicative pollen or plankton, and others. In order to form a climate/period measuring series, it is necessary to perform several interim steps: correction functions, dating and finally the calibration with climate data, which is not without problems. As far as the tree rings are concerned (Fig. 6.7), the decisive aspects are those facts to which the tree growth reacts and has reacted in the past (temperature, precipitation, season), or the question how much the tree or the group of trees is typical for the regional climate. .

Fig. 6.7: The width of tree rings indicates temperature and humidity of the individual years. It is possible to create a complete sequence of tree rings for the past 8,000 to 9,000 years by aligning tree rings of old trees the age of which is known, and by overlapping tree rings of historical and archaeological wood finds 80 Only by means of instrumental measurements it is possible to calibrate all climate proxies. This means that depending on the location it is not possible to go further back than 1900. Therefore it is necessary to clarify whether a transfer function which has been deduced from the 20th century in fact can be adapted to earlier centuries. Another problem concerning the tree rings is that the current CO2 enriched atmosphere could have influenced the calibration of tree ring data for the C-14 age determination. Notwithstanding all these difficulties, is has repeatedly proven that it is possible to reconstruct climate because independent archives (ice cores, sediments, tree rings) often coincide well (Brönnimann 2004/05). The calibrated time measurement series alone is only an incomplete picture of the climate because it is relevant only for a certain location. If a number of such series exist for a certain region, it is tried to extract the interesting data, such as the average temperature of the Northern hemisphere, by means of reconstructive methods. The standard procedure is the multiple regression by which first of all the number of variables is reduced by an analysis of the principle components (PCA, Principal Component Analysis), which is a statistical standard method. This avoids that imprecise, unimportant or erroneous information is included in the reconstruction. The predictive data (e.g. tree ring series) have to be existent not only for the period to be reconstructed, but also for a "calibration period" which should be as long as possible and for which the variable which is to be reconstructed exists (e.g. for the period between 1900 and 2000). Principal component analysis and regression model are statistically adjusted, and the parameters gained from them are used in order to invert the procedure for the past (Brönnimann 2005). The temperature diagram of the past 1,000 years Mann had reconstructed in 1998, has the form of a hockey stick - a slight decrease of the temperature until approx. 1900, and then a steep increase (Fig. 6.6). For the reconstruction, a lot of available climate data of the past centuries was used, among others measurement data of meteorological stations, but also indirect climate data, the so-called proxydata, data from sediments, ice core analyses of the polar ice, tree ring analyses, corals and further data. By means of the principle component analysis, the temperature development was determined from more than 70 different climate records. The IPCC used this diagram in its 3rd Assessment Report (TAR) as an indication for the anthropogenic greenhouse effect, because the temperature rise coincided with the increasing combustion of fossil fuels.

The Hockey Stick Discussion The so-called hockey stick diagram has led to intensive discussions amongst the scientists. More recent calculations (McIntry and McKitrick 2003, 2004, von Storch 2004, 2005) have proven that most likely methodical errors were made during the computer-based evaluation of the basic data which are said to inevitably lead to this form of graph. Von Storch 2004 states that due to the regression-based method, the temperature variability of the Northern hemisphere is underestimated by a factor of 2. In von Wahl 2006, this statement is attributed to a miscalculation. According to von Storch 2006, this overestimation is preserved all the same. Also Bürger and Cubasch 2005 showed that the used instrument data is not suitable for calibrating the regression model employed. On the other hand, next to the studies by Mann (1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005) and Rutherford 2005, there are numerous other publications (Bradley 2001, Briffa 2001, Esper 2002, 2005, Soon 2003, Huang 2004, Jones 2004, Widmann 2003), (Fig. 6.8) which show a similar course of graph but with considerable fluctuations particularly around 1100 - 1200 during the so-called Me- dieval Warm Period (MWP) and the Little Ice Age (LIA) around 1700. All these curves are (just) still within the range of uncertainty of Mann's curve. In a new study, Wahl and Ammann 2006 show that the temperatures reconstructed by Mann are robust at least since 1400, independently of the possibly wrong mathematical use of the so-called principle component analysis. According to these findings, the temperatures of the early 15th century had to be corrected only slightly by 0.05 °C. 81

Fig. 6.8: Temperature development since 850 according to different reconstructions (Moberg 2005). None of the reconstructions proved higher temperatures than have been measured in the past decades

Despite the controversial or wrong use of the principle component analysis, other studies confirm Mann's graphs with their uncertainty range because in this special case, this method has no significant influence on the method used by Mann and thus leads to only small deviations (Zorita 2005, von Storch 2005, Huybers 2005). Nor has Moberg 2005 (Fig. 6.8) for the last 2,000 years found a warmer period than that after 1990, but he stated that the climate variability of the last centuries, with a clear temperature increase in the Middle Ages, has been bigger than assumed so far. Today, the majority of the climate scientists assume the existence of the Medieval Warm Period (MWP) and the Little Ice Age (LIA) with corresponding temperature fluctuations. Osborn 2006 confirmed this fact by statistical analyses, and he found that the warming in the 20th century was the most pronounced and most extensive one. After having carried out extensive simulations with a tridimensional coupled atmosphere/ocean model, Cubasch 2006, too, states that the temperature fluctuations of the past 1,000 years have been bigger.

After extensive literature evaluation, the new study of the US-American National Academy of Science (National Research Council 2006) concludes that the global warming has currently reached its highest level for the last 400 years. For the years between 1000 and 1600, the data is not very clear any more, but none of the reconstructions shows that the temperatures during the Medieval Warm Period were higher than those of the past decades. In its report, the committee adds that the proof of the anthropogenic influence on climate is completely independent of the question whether the so-called hockey stick graph is correct or not.

The discussion about the temperature trend of the last 1,000 to 2,000 years has not yet fin- ished, as have shown the most recent commentaries of Wahl 2006, Rahmstorf and von Storch 2006 in Science, as well as the Wegman Report 2006 for the US House of Represen- tatives (http://energycommerce.house.gov/108/home/07142006_Wegman_Report.pdf). IPCC 2007 states that average Northern Hemisphere temperatures during the second half of the 20th century were very likely higher than during any other 50-year period in the last 500 years and likely the highest in at least the past 1300 years (SPM, IPCC 2007).

6.1.6 Urban Heat Islands There was an intensive discussion about the influence of urban heat islands on the temperature increase of the past 150 years, because it is a fact that the average temperatures in metropolitan areas are clearly higher than their surroundings, particularly at night. Addition- ally, urban areas have significantly grown in size in the past decades. Yet, extensive research (IPCC 2001/07, Peterson 2003, 2005) has shown that the effect of the urban heat islands does not contribute more than 0.05 °C to the global temperature development for the 82 period from 1900 to 1990. Thus, it is practically of no influence on the global temperature rise. Parker 2004, 2006 has shown that the temperature increase above land was equally strong in windy as in calm nights. This indicates that the observed global warming is not a consequence of the urban development, because the effect of the urban heat islands ap- pears particularly at night and in times of weak wind.

6.2 Regional Climate Changes The evaluation of regional and seasonal trend analyses draws a complex picture. Next to regions with temperature increases, there are also regions which have cooled down in the last 100 years. The so-called global warming does not exclude dropping temperatures limited to certain areas (Fig. 6.9). The average value for the last century shows that particularly the Euro-Asian region and parts of America have clearly warmed up.

Fig. 6.9: Regional distribution of the linear temperature trend from 1901 to 2000 (annual values in ° C, K) (from: Schönwiese 2006, source, Jones 1999, CRU 2005))

As an example, the areas above the North Atlantic or Central Africa, as well as in the high latitudes, cooled down. Fig. 6.10 shows the temperature changes of 1980 – 1999. Afterwards, there is a clear temperature rise particularly in the Asian region, in Central Europe, Scandinavia, parts of Can- ada and above the North Atlantic. Especially some areas above oceanic regions experienced cooling.

Fig. 6.10: Regional temperature trend 1980 -1999, next to warming regions, there are also cooling regions (from Schönwiese 2006, source of data: Jones 2002, analyses: Fundel/Schönwiese 2002)

Evaluations made by NASA for the period from 1900 to 2005 prove a similar warming and cooling behaviour, as shown in Fig. 6.11. Areas which have cooled down, are located particularly in Central Africa and South America. Clear temperature increases can be seen in North America and parts of Asia. On a whole, the regions that are warming are meanwhile predominant. In this period, the terrestrial surface has warmed by approx. 0.8 °C (Hansen 2006).

Fig. 6.11: Changes of the terrestrial surface temperature between 1900 and 2005, based on local, linear trends of the surface temperature of the air above land and the sea surface temperature (Hansen 2006) 84 There were significant regional changes not only in temperature, but also in precipitation in the 20th century (Fig. 6.12).

Fig. 6.12: Regional distribution of the precipitation trend between 1900 and 1999, proportional trend of the annual precipitation amount, global analysis (IPCC 2001); the figures on the right state the values for the marked latitudes around the globe (Schönwiese 2006)

The regional distribution of the precipitation trend for the years 1900 until 1999, shows areas with a clear increase and others with a decrease in precipitation. In particular for Central Af- rica and the West coast of South America, the decrease was pronounced. Increasing precipitation could be observed, especially for North America, Central Europe and Australia. Also the Sahel (Northern Africa) experienced increased precipitation. According to IPCC 2007, long-term trends from 1900 – 2005 have been observed in precipitation amount over many large regions (eastern parts of North and South America, northern Europe and northern and central Asia) (SPM, IPCC 2007).

6.2.1 Climate Trend in Asia Since the 80s of the 20th century, China has experienced a clear climate change. The summer rain belt has moved, and most of the summers were characterised by droughts. Its cause is assumed to be growing soot and sulphate emissions and forest clearings which could have contributed to a reduction of the measured solar insolation (Fig. 6.13) (Xu 2001, Menon 2002, Hansen 2002).

Fig. 6.13: Regional climate changes in China due to changes of solar insolation (red), precipitation (blue) and monsoon belt (green) in summer (HBS, Kasang 2005 according to Xu 2001)

Model calculations have shown that black carbon (soot) and sulphate emissions influence the air circulation by changing the radiation conditions, and thus change the precipitation amount in the North and South of China in a contrasting manner. According to Menon 2002, this could be the reason for heavier rainfall in the South, and for intensified droughts in the North of China in the last decades. Due to model calculations and observations, Ramana- than 2005 fears that the number of droughts could double in the next decades in China, if the aerosols continue to increase.

6.2.2 Climate Trend in Europe and Germany

Europe

Europe has warmed more than the global average, with a 0.95 °C increase since 1900. Temperatures in winter have increased more than in summer. The warming has been greatest in northwest Russia and the Iberian Peninsula. In the past 100 years the number of cold and frost days has decreased in most parts of Europe, whereas the number of days with temperatures above 25 °C (summer days) and of heatwaves has increased.

Annual precipitation trends in Europe for the period 1900–2000 show a contrasting picture between northern Europe (10–40 % wetter) and southern Europe (up to 20 % drier). Changes have been greatest in winter in most parts of Europe. Glaciers in eight out of the nine glacier European regions are in retreat, which is consistent with the global trend. Sea levels around Europe increased by between 0.8 mm/year (Brest and Newlyn) and 3.0 mm/year (Narvik) in the past century (EEA 2004).

Germany The last 10 years of the 20th century were the warmest decade of the century in Germany and world-wide. Nine of these years lay above the long-term average temperature value of 8.3 °C. 2000 was the warmest year of the past century. All in all, for the period between 1901 and 2003, a statistically significant temperature increase of 0.8 °C was experienced in Germany. As shows Fig. 6.14, this increase was not a constant one. The increase until 1911 was followed by a very warm period starting in 1988. Figure 6.16 shows a similar picture for the period between 1761 and 2000 (Schönwiese 2003). 86

Fig. 6.14: Annual average day temperature trend in Germany between 1901 and 2005 (green: individual values, pink: mean value 1961 – 90, orange: linear trend) (DWD 2004, source: UBA 2006 from DWD 2006)

In the 20th century, all seasons contributed to the temperature trend nearly to the same extent. In the last two decades, particularly the winter warming increased at 2.3 °C, compared to the summer warming of 0.7 °C, whereas the autumn warming has come to a standstill (Fig. 6.15). In the last century, and particularly during the last three decades, the winter precipitation has significantly increased (Schönwiese 2003, 2005a).

Fig. 6.15: Overview of the observed temperature (above) and precipitation trends in Germany between 1901 and 2000 (spring, summer, autumn, winter, year) (Rapp 2000; Schönwiese 2003, 2005, source: Schönwiese 2005a) The summer of 2003, with an anomaly of 3.4 °C above the average value for the period between 1961 and 1990, was the warmest summer since 1761. There has also been a trend towards an increase of hot days in Germany for some decades (Schönwiese 2003, 2004, 2006). 87 In Central Europe, there are measurement series from several stations which date even further back to the 18th century and which show temperatures that are as high or even higher than those of today. First of all, these measuring series do not show an appreciable trend for the complete period, like this is reflected e.g. in the measurement series of Hohenpeißen- berg, Germany. For these stations, the warming just seems to be a recovery from a cool phase in the 18th century (DWD 2002). Yet, the warming trend is maintained in the German area mean since 1761 (Fig. 6.16), also for Hohenpeißenberg (Böhm 2006). The strong winter temperature increase of the past 30 years can be correlated to the positive NAO index for this period (Tinz 2002).

Fig. 6.16: Year anomalies of the area mean of air temperature near ground level for 1761 - 2004 in Germany. The trend function is non-linear, but since 1901, it is linear in good approximation and indicates a warming of approx. 1 °C. Some relatively warm and cold years are stated (including the so far existing heat record in 2000) (data according to RAPP 2000, supplemented according to DWD, from Klimatrendatlas Deutschland 1901 – 2000, Schönwiese 2005a)

Regional temperature trends are mainly influenced by circulation anomalies that can either enhance or weaken a global anthropogenic trend. Therefore, regional temperature trends only allow for very limited conclusions about anthropogenic influences.

6.3 Troposphere - Satellite Measurement For years, experts have intensely discussed the (supposed) discrepancy in the temperature trend near the ground and in the troposphere. It was the reason for doubting the anthropogenically caused climate warming, because according to the climate models, a slightly stronger warming should have taken place in the troposphere than near the ground. Data evaluation in the past 15 years showed a negative trend at first, but after continuous corrections, the trend was positive. The difference to the ground data was stated particularly for the tropics and subtropics.

Satellite Measurements Since 1979, polar-orbit satellites have been observing the earth's atmosphere nearly completely. The two satellites (MSU, AMSU) operated by the US American national "weather authority", NOAA, allow indirect temperature and humidity measurements in the lower troposphere by measuring the radiance in different spectral ranges. High-resolution spectrometers (Microwave Sounding Unit, MSU) measure the microwave radiation of oxygen. Oxygen is

88 used, because temperature profiles can only been drawn up if the dispersion of the examined molecules in the atmosphere is known and possibly regular. By means of radiance (= radiation flux per area unit and solid angle), the temperature is determined by Planck's radiation formula (see chapter 3.3). The radiation intensity is proportional to the temperature in broad vertical layers of the troposphere. The incident radiation is measured in different frequencies, and each of the differing frequency channels comprises a certain area of the atmosphere that may overlap e.g. towards the lower stratosphere. Radiation fluctuations at different frequencies near a spectral line allow the determination of temperature profiles. The NOAA satellites are near-polar, solar-synchronous satellites for which the local solar time of certain geographic latitude nearly always is the same at the moment the satellite crosses it. This means that a certain spot on earth is always crossed at the same local time. With a mean orbit altitude of 860 km, the orbital period above the poles amounts to approx. 106 minutes (www.palmod.uni-bremen.de/~amma/diss/). Particularly difficult is the evaluation of time series from by now nine different micro transmit- ters in the satellites that are following each other, because a satellite may sink down during its lifetime, and because of its time drift in relation to the local solar time, which has to be calculated and cleared. After their first publication in 1990 (Christy, Spencer), the calculated temperature trends were corrected several times (Christy 2003, 2004, Spencer 2004, Hase 2005) in the subsequent 15 years. By means of the data of radiosondes it was tried to verify the data, procedure which was difficult because it was not directly measured but deviated. Yet, also in this area problems arose because the two measuring systems are comparable only to a certain extent. On the one hand, the measurements were not made at the same time, and on the other hand the radiosonde delivered a point measurement and the satellite a measured area of at best 1 km2. Additionally, both procedures are impaired by measurement errors (measurements by radiosondes: uncertainty around 0.3 °C). In 2004, Fu stated that the strong temperature decrease of 0.5 to 0.9 °C per decade in the stratosphere, which was found in the last two decades, most probably has influenced the temperature trend in the troposphere. According to Fu, only 85 % of the sampled microwaves that are used for the temperature determination, originate from the troposphere. The rest originates from the stratosphere which has clearly cooled down. If the temperature values are corrected by these findings, they result in a positive temperature trend of 0.17 °C. In August 2005, three papers were published about this topic (Mears et al., Santer et al., Sherwood et al. 2005), which contributed new findings to this question. As the interpretation of the measurement data was extremely difficult, since 1978, when the measurements were started, many corrections were made in order to correct the errors which were recognised. Two groups in the USA – the UAH group (Spencer and Christy), and the RSS group (Wentz, Mears and colleagues) - concerned themselves with the evaluation and for years had differing results, which however continuously were approximating. Thus, one of the first problems which was recognised was the satellite drift. It was caused by the slowly sinking in the course of years, and it falsified the values. Other errors were due to the fact that because of their short operating time, satellites had to be replaced within some years, and the satellite data were inexact. In 2005, after new corrections, the RSS group found a higher trend of 0.19 °C, whereas the UAH group rose its trend from 0.086 to 0.12 °C per decade in May 2005 (Fig. 6.17). Mears 2005 equalised the differences by a correction factor which considers the fact that the satellites do not always orbit the same location at the same time. In practice, these positions vary slightly. Santer 2005 compared the corrected values with calculations from 19 different models and found that the corrected values concurred well. Sherwood 2005 proved the earlier reasoning in favour of the low temperature trend – that is the correlation with the radiosonde measurements of weather balloons – to be flawy, too, because the measurements were inexact, and particularly the measurements in higher latitudes were taken for comparison. Measurements carried out by means of weather balloons are not exact because due to the solar insolation, some measuring instruments warm up to a greater extent than others. It was striking that the temperature differences between day and night 89 have constantly minimised since the 1970s. In order to consider the solar heating of the measuring instruments during the day, the read value was corrected downwards. Due to the fact that the insulation of the measuring instruments against solar radiation had improved over the last years, yet the measured values continued to be corrected downwards by the same value, the actual warming was in fact underestimated. The discussion about the warming in the troposphere surely is not concluded yet, because the exact evaluation of satellite data still is connected to considerable uncertainties. In the past years, numerous special publications have been published about this topic (Spencer, Christy, Mears, Stabile, Wentz, Vinnikov, Groggy, Schiermeier, Jinn, Dickinson, Alit. R.C. Balling, Curvy, Teat etc.). Nevertheless, it becomes increasingly clear that due to the approximation of both evaluation groups concerning the determination of the warming rate, the latter coincides more or less with the model calculations. Spencer of the UAH group (www.Marshall.or/article.phi?id=312) explains the still remaining difference of 0.12 to 0.19 °C with the differing calibration of the time series of two subsequent satellites.

1980 1985 1990 1995 2000 2005 Fig. 6.17: The graph shows the latest corrected evaluations of the positive temperature trend in the lower troposphere (RSS: 0.19 K/decade, UAH: 0.12 K/decade); the stronger warming due to El Niño events is clearly visible (e.g. 1997/98), actual state Sept. 2005 (www.ssmi.com/msu/)

The observed temperature decrease in the stratosphere is - in correlation to the models - caused by the ozone depletion and the increase of greenhouse gas emissions (Fig. 6.18).

Fig. 6.18: The graph shows the latest corrected evaluations of the temperature trends in the lower stratosphere, with a clear cooling (RSS: -0.32 K/decade, UAH: -0.44 K/decade) and a short-term warming after the volcanic eruptions of El Chicon in 1982 and Mt. Pinatubo in 1991 (http://www.ssmi.com/msu/msu_data_description.html#msu_amsu_trend_map_tlt) As shown in figure 6.17, the troposphere has warmed by 0.12 – 0.18 °C per decade since 1979, whereas the stratosphere has cooled by 0.322 – 0.445 °C per decade during the same period (Fig. 6.18). Clearly detectable are short-term warmings of the lower troposphere due to El Niño events and big volcanic eruptions. Figure 6.19 shows that the warming rate differs for the varying regions. The strongest warming occurs around 40 °N and approx. from 60 °N upwards. 90

Fig. 6.19: Warming of the lower troposphere between 1979 and 2004, decadic trend (MSU Kanal TLT). Data of regions that are polewards 82.5° North and 70° South, and of areas with land or ice elevations of over 3000 m, are not available and marked white After another correction of the UAH data, Vinnikov 2005 finds a global warming trend in the troposphere of 0.20 °C per decade. The research report of the American climate research programme published in June 2006 (Karl 2006) confirms that the earlier discrepancies are not existent anymore and that in the past decades a warming had taken place both near ground level and in the lower atmosphere, which correlates to the climate models. IPCC 2007 states that the discrepancy noted in the TAR is now reconciled (SPM, IPCC 20079). 91 7 Climate Research Institutes and Programmes For several decades, numerous international organisations have concerned themselves with the scientific contexts of climate change and its possible consequences, and with considerations about how to avoid or adapt to climate changes that possibly are to be expected. Vari- ous international and national research programmes have been initiated.

7.1 IPCC In 1988, the World Meteorological Organisation (WMO) and the United Nations Environment Programme (UNEP) founded an international intergovernmental committee, the Intergov- ernmental Panel on Climate Change (IPCC), in order to collect and analyse all information about climate changes. In 1992, the environment conference of Rio de Janeiro adopted the United Nations Framework Convention on Climate Change. The further stages of international climate protection are shown in Fig. 7.1.

Stages of International Climate Protection Before four PrepComs 1992 1992 United Nations Conference on Environment and Development (UNCED) Rio de Janeiro – signature of the Framework Convention on Climate Change 1994 Framework Convention on Climate Change enters into force 1995 First Conference of the Parties (COP) in Berlin 1996 Second COP in Geneva 1997 Third COP in Kyoto – adoption of the ‘Kyoto Protocol’ 1998 Fourth COP in Buenos Aires - adoption of the "Buenos Aires Action Plan“ 1999 Fifth COP in Bonn 2000 Sixth COP in The Hague 2001 Sixths COP continued in Bonn – adoption of the "Bonn Agreement“ 2001 Seventh COP in Marrakech 2002 Eighth COP in New Delhi 2003 Ninth COP in Milan 2004 Tenth COP in Buenos Aires 2005 Eleventh COP and first MOP in Montreal, Kyoto Protocol come into force 2006 Twelfth COP in Nairobi

Fig. 7.1: Stages of international climate protection from 1992 to 2005. After the Kyoto Protocol had come into force on 16 of Feb. 2005, the Members of the Protocol (MOP) met for the first time (source: Schafhausen 2005, BMU, completed)

IPCC is an international expert panel of hundreds of scientists of different disciplines, who document the state of the art of the worldwide research on climate change in their reports and publications. The most important committees of IPCC are shown in Fig. 7.2.

92 Central Bodies of the International Climate Protection Scheme IPCC: Intergovernmental Panel on Climate Change (established by WMO and UNEP) COP = Conference of the Parties = top body UNFCCC Subsidiary Bodies - SBSTA: Subsidiary Body on Scientific and Technological Advice - SBI: Subsidiary Body on Implementation MOP = Meeting of the Parties = top body Kyoto Protocol Climate Secretariat

Fig. 7.2: Important committees of IPCC (source: Schafhausen 2005, BMU) The structure of the organisation of the UN Framework Convention on Climate Change with its subcommittees and the IPCC Secretariat is shown in Fig. 7.3. The Conference of the Par- ties (COP) is supported by the IPCC Secretariat and subordinated groups, like SBI, which is responsible for questions of the implementation, and SBSTA, responsible for scientific and technological advice.

Fig. 7.3: Representation of the Organisation of the UN Framework Convention on Climate Change (source: UNFCC)

7.1.1 The IPCC Working Groups All nations that are members of WMO or UNEP, are also members of IPCC and its three working groups which deal with the various aspects of climate change (Fig. 7.4). The first working group (WG1) deals with the scientific findings about climate-influencing factors. The second working group (WG2) assesses the ecological and socio-economic effects of global warming for the living space which is the earth, and the third working group (WG3) analyses possible strategies for combating the greenhouse effect. The first two reports of the three working groups were published in 1990 and 1995. It was already stated in the first report that: "The anthropogenic influence on the global greenhouse effect is probable. Therefore, it is recommended to take preventive measures. “

Fig. 7.4: Organisational structure of IPCC with its 3 working groups (source: UNFCC) In 2001, the Third Assessment Report (TAR) was published entitled "Climate Change“. The three volumes comprise a total of 2,696 pages and were drawn up by 455 lead authors and further 839 contributory authors. They were helped by 72 review authors who surveyed the inclusion of proposals for changes by the over 1,000 expert and government consultants. In the procedure for the drawing-up of these reports, all commentaries and objections were screened and dealt with by review editors. Controversies about certain topics were expressly mentioned, and the probability rating was lowered when deviating results or opinion existed. TAR consists of three volumes which were each drawn up by the respective working groups: - The Scientific Basis (IPCC 2001) - Impacts, Adaptation and Vulnerability (IPCC 2001a) - Mitigation (IPCC 2001b) For each volume, there is a Summary for Policymakers (SPM) and a Technical Summary (TS) available. In several plenary sessions, the first was subject to a line-by-line "approval". Controversial wordings had to be adopted unanimously. The TS is not subject to such a complicated procedure but has to be "accepted" by the general assembly. The Synthesis Report (SR) (IPCC 2001c) contains an abstract of the three reports and answers a series of questions. This SR also had to be approved. Meanwhile, these reports have been published in German. Since the first report was published in 1990, knowledge about numerous contexts described in it has been ascertained and completed, and significant progress has been made in the understanding of climate changes. Nevertheless, many statements are still subject to smaller or bigger uncertainties. In order to prevent criticism, a very differentiated system of probability factors was introduced as a means for dealing with the uncertainties. In particular in Working Group I "The Scientific Basis", an indicative system was introduced for statements like "highly likely" (90 – 99 % probability), "likely" (66 – 90 % probability) till "extraordinarily 94 unlikely" (< 1 % probability). Unfortunately, this assessment system has not been kept up quite consistently. The Working Group I Summary for Policymakers (SPM) of the 4th Assessement Report (AR4) was published on 2 February 2007; the report was produced by around 600 authors from 40 countries, and reviewed by over 620 experts and governments. The indicative system was changed a little: e.g. “very likely” means 90 – 95% probability of occurrence.

7.1.2 Important Findings of the 3rd and 4th IPCC Report (TAR, AR4) The first report "Scientific Basis" (TAR) draws the following conclusions: A growing number of observations draws a collective picture of a warming world: In the 20th century, the global average temperature rose by 0.6 +- 0.2 °C. On a global level, it is likely that the 1990s were the warmest decade, and 1998 the warmest year since the beginning of the instrument measurements in 1861. The temperature increase of the past century is likely to have been the most pronounced one for the last 1,000 years. In the 20th century, the average global sea level rose by 10 to 20 cm, and the ocean heat content has increased. With few exceptions, the extension of snow and ice covers has decreased. Precipitation is increasing in central and high latitudes of the Northern hemisphere - in particular due to heavy precipitation -, in the tropical areas it is decreasing. There is new and clearer proof of the fact that the major part of the warming observed in the last 50 years must be attributed to human activities. Owing to human activities, the concentration of atmospheric greenhouse gases and their radiative forcing have continuously increased. In the light of recent evidence, and considering the remaining uncertainties, the major part of the observed warming in the course of the past 50 years is probably to be attributed to the increasing greenhouse gas emissions. Human influences will continue to change the atmospheric composition in the course of the 21st century. For the period from 1990 to 2100, an average global temperature increase near ground level of 1.4 °C to 5.8 °C is predicted. Snow coverage and the extent of the sea ice in the Northern hemisphere will continue to decrease, and glaciers and ice caps will continue to retreat. In the period between 1990 and 2100, the average global sea level is predicted to rise by 0.09 to 0.8 m. The second report "Impacts, Avoidance, Adaptation" deals with the repercussions of climate changes. First, an attempt is made to try and assess the influence of climate changes on natural and near-natural systems (water resources, agriculture, forestry, and ecosystems like coral-reefs, mangrove forests, habitats in the Arctic and mountains, swamps, prairies and glaciers), and on human systems like health, settlements, energy, industry, insurance industry etc. Regional analyses try to work out the special susceptibility of various regions and countries to climate changes. The knowledge of such specific susceptibilities is the basis for the development of specific strategies for adaptation. The countries with the smallest resources, like Africa, consequently have the smallest capacities for adaptation. In this respect, questions of "fairness" and "sustained development" are of special importance, e.g. in the case of the small island countries which could particularly be affected by a sea level rise. Also according to the opinion of German specialists (3rd German IPCC Strategy Workshop in 2002), the current state of knowledge is completely insufficient. Therefore, the attempts for developing "adaptation" measures for individual regions and/or sectors are said to remain in- adequate. The third Report assesses "the scientific, technological, environmental, economic and social aspects of the mitigation of climate change". Here, mitigation of climate changes is defined 95 as measures initiated by mankind in order to reduce greenhouse gas emissions or to increase sinks. For the Third Assessment Report, IPCC decided on an interdisciplinary approach with the objective to assess options for the reduction of greenhouse gas emissions or for strengthening sinks with regard to a cost-benefit analysis. Also for this topic, aspects of fairness and sustained development are of utmost importance. However, the development of political concepts and strategies for adequate measures for the limitation of an increase of greenhouse gases is of very general character, and due to the complexity, their deliberation has not yet come to conclusion. As was the case for the previous report, critics find fault with an allegedly excessive exertion of political influence, in particular in the summaries for policymakers. They argue that many of the critical and also deliberating ideas are missing in the summaries, which in the long version of the reports are dealt with to the full extent. On the other hand, one has to understand that many different interests come together in the IPCC which will only find a majority if extreme, pointed statements give way to compromise wording. A committee of the US American National Academy of Science (NAS 2001) called the report of WG 1 "an admirable summary of research activities in climate science“. Meanwhile on February 2007, the summary for Policymakers of the 4th Assessment Report (AR4) was published. The findings of the 3rd Report were confirmed and even emphasised (see also chapter 8.2.3). The main findings are: • The world’s average surface temperature has increased by around 0.74°C over the past 100 years (1906 - 2005). This figure is higher than the 2001 report’s 100-year estimate of 0.6°C due to the recent series of extremely warm years. • The amounts of carbon dioxide and methane now in the atmosphere far exceed pre- industrial values going back 650,000 years. As stated above, concentrations of carbon dioxide have already risen from a pre-industrial level of 280 ppm to around 379 ppm in 2005, while methane concentrations have risen from 715 parts per billion (ppb) to 1,774 in 2005 • If atmospheric concentrations of greenhouse gases double compared to pre- industrial levels, this would “likely” cause an average warming of around 3°C, with a range of 2 - 4.5°C. For the first time, the IPCC is providing best estimates for the warming projected to result from particular increases in greenhouse gases that could occur after the 21st century, along with uncertainty ranges based on more comprehensive modelling. • Best estimates and likely ranges for globally average surface air warming for the low scenario (B1) is 1.8°C (likely range is 1.1°C to 2.9°C), and the best estimate for the high scenario (A1FI) is 4.0°C (likely range is 2.4°C to 6.4°C). • The best estimates for sea-level rise due to ocean expansion and glacier melt by the end of the century (compared to 1989 – 1999 levels) have narrowed to 28 - 58 cm, versus 9 - 88 cm in the 2001 report, due to improved understanding. However, larger values of up to 1 m by 2100 cannot be ruled out if ice sheets continue to melt as temperature rises. • Sea ice is projected to shrink in both the Arctic and Antarctic regions. Large areas of the Arctic Ocean could lose year-round ice cover by the end of the 21st century if human emissions reach the higher end of current estimates. The extent of Arctic sea ice has already shrunk by about 2.7% per decade since 1978, with the summer minimum declining by about 7.4% per decade. • Snow cover has decreased in most regions, especially in spring. The maximum extent of frozen ground in the winter/spring season decreased by about 7% in the Northern Hemisphere over the latter half of the 20th century. • It is “very likely” that precipitation will increase at high latitudes and “likely” it will decrease over most subtropical land regions. The pattern of these changes is similar to what has been observed during the 20th century. • It is “very likely” that the upward trend in hot extremes and heat waves will continue. The duration and intensity of drought has increased over wider areas since the 1970s, particularly in the tropics and subtropics. The Sahel, the Mediterranean, southern Africa and parts of southern Asia have already become drier during the 20th century.

96 A number of widely discussed uncertainties have been resolved. The temperature record of the lower atmosphere from satellite measurements has been reconciled with the ground- based record. Key remaining uncertainties involve the roles played by clouds, the cryosphere (glaciers and ice caps), oceans, deforestation and other land-use change, and the linking of climate and biogeochemical cycles (SPM, IPCC 2007)

7.2 Research Programmes Since the beginning of the 1980s, many climate research programmes have been launched worldwide. In 1980, the World Climate Research Program (WCRP) was founded by the ICSU (International Council of Science) and the WMO (World Meteorological Organisation). Its aim is to determine to which extent it may be possible to predict natural climate fluctuations and the anthropogenic influence. To this end, research should concentrate on a description of the current condition of the climate, the forming of models, the decisive climate processes and future climate trends (Lemke 2003). In the following, the most important subprogrammes are listed (www.wmo.ch/web/wcrp/prgs.htm): Since 1994, the Arctic Climate System Study (ACSYS) and its succeeding project Climate and Cryosphere (CLIC) have focussed on the observation and modelling of the Arctic Ocean and the atmosphere above it, as well as on the role the Arctic plays in the climate system. The CLIC project researches on the entire global cryosphere. Since 1995, the CLIVAR project (Climate Variability and Predictability Programme) has been concerned with the basis of natural climate variabilities and predictability of the global coupled climate system. The Global Energy and Water Cycle Experiment (GEWEX), Strato- spheric Processes and their Role in Climate (SPARC) and World Ocean Circulation Experi- ment (WOCE) are further sub-programmes of the WCRP. Important for the development of models are also the Working Group on Coupled Modelling (WGCM), as well as the two IGBP programmes Global Analyses Integration and Modelling (GAIM) and Coupled Model Inter- comparison Project (CMIP), which carries out comparisons between the individual models. In addition to them, there are numerous further international, but also national research programmes, like the DEKLIM programme in Germany (www.deklim.de) and a very extensive programme in the USA, the so-called Climate Change Science Programme (CCSP) (www.ccsp.gov), (http://www.climatescience.gov/about/default.htm). For the American research programme, the financial framework is planned to amount to 20 billion US$. Also the European Union carries out numerous research programmes (ACACIA, MICE, PRUDENCE). 97

8 Climate Models and Model Results Climate models based on physics first of all help in the understanding of today's climate, and then, based on it, the simulation of climate situations of the past as well as of those to be expected in the future. As is common practice for most of the models, the complex processes and structures of interaction in the real world have to be represented in a simplified manner. The extent of simplification varies strongly depending on the model type. Models represent (Brönnimann 2004/05) the sum or the integration of our physical knowledge about the atmosphere. They try to simulate the atmospheric processes on the basis of physical laws, mathematical equations and a large amount of parameterisations for processes which can only be described by their effects. Models are not a perfect but an important tool for climate research. It is the objective of present climate models to draw a picture of the reality which is as realistic as possible by incorporating a preferably large amount of relevant processes. Models describe only a part of reality, as it is not possible to include all the processes and parameters (von Storch 2003).

8.1 Climate Models

Climate models describe the climate system of the earth in physical-mathematical equations, which a computer can solve numerically. They consist of a combination of basic physical laws which calculate the most important atmospheric processes and state variables by means of differential equations. To the largest possible extent, they represent the interactions of the individual parts of the complex climate system and their internal processes of change. From them, the computer "calculates" the succession of weather events, which is the characteristic repartition of the most frequent average and extreme weather conditions and procedures for a certain location or larger area. From the results, the weather statistics - which is the climate - are derived (von Storch 2005). Energy balance models have the simplest structure of all climate models. From the balance of solar insolation and terrestrial reflection, the average global air temperature near ground level is calculated. The two-dimensional radiation/convection models consider the exchange of impulse, energy and masses, while recording temperature, humidity and radiation flux in vertical direction. They help to determine the influence of radiation, cloud formation and convection on the global climate. These simple approaches have their justification in the quick determination of the statistical behaviour of individual climate elements. A complete climate model should contain the physical description of all climate components and allow for their coupling (Fig. 8.1). The climate system of the earth (chapter 1.1) consists of 5 components: the atmosphere as the setting of weather interacts with the hydrosphere (sea and water circulation), the cryosphere (ice and snow), the biosphere (plants and animals), the geosphere (soil and rock). The interactions occur on very differing time scales from hours (clouds, atmospheric pressure) to millenniums (ice masses). Difficulty is caused by the consideration of so-called non-linear interactions by small internal disturbances which may have big effects ("butterfly effect") (Cubasch 2003). Also external factors have to be considered in the model calculations, like changes in solar insolation, volcanism and mankind with the additional greenhouse effect and changes in the use of land.

Fig. 8.1: Scheme of a coupled atmosphere/ocean model and supplementary models http://www.atmosphere.mpg.de/enid/ACCENTen

In the following, the most important model types are listed (according to MPI, Brönnimann 2004/05): - Atmospheric models (GCM, atmospheric circulation) - Ocean/atmosphere models (OAGCM or AOGCM, coupled model with oceanic and atmospheric circulation) - Chemical climate models (CCM, coupled model with atmospheric circulation and atmospheric chemistry) - Chemical transport models (CTM, chemical model without circulation) - Earth system models (ESM, modular modelling system with atmosphere, sea, soil surface processes, biosphere etc.) Fig. 8.2 shows the chronology of model development in the last 30 years according to IPCC 2001. In order to be able to include all interactions, the models constantly become more and more complicated and complex. 99

Fig. 8.2: Chronology of the climate model development (as of the year 2000) according to IPCC 2001. The inclusion of various more recent components like carbon circulation, vegetation and atmospheric chemistry, leads to a drastic increase in the complexity and calculation time of the climate models. Yet, it is a necessary development in order to gain a growing amount of quantitative model results

8.1.1 Coupled Atmospheric Circulation Models At present, the climate models physically depict "only" atmosphere, landmasses and sea as individual systems and in their interactions. The remaining subsystems of the climate are included only in a generalised manner. Perhaps the biggest advance in climate modelling in the past 15 years has been to couple atmospheric models (GCM) to dynamic models of the ocean (AOGCM) (Scaife 2007). In this complex model systems (AOGCMs) the ocean is fully simulated which also take into account the feedback with sea-based and land-based ice sheets and continental surfaces. In order to solve these equation systems with the computer, the earth's atmosphere and the sea are split up into grid cells. Today, they have a horizontal resolution of around 200 to 500 km and of 8 to 20 vertical layers, for the sea they have up to 30 layers. Due to the high dynamics of atmospheric processes, also high resolution in terms of time is necessary for the GCM. The intervals normally comprise between 30 to 60 minutes. This requires extraordinarily long calculation times of sometimes several months on modern large-scale data-processing systems. It is not possible to model physical-chemical processes that occur within a grid cell. They have to be included in the model by parameterisation, which means that they have to be derived from known meteorological regularities of the grid cell edges. This applies to processes like e.g. convection, boundary layer processes, cloud formation, precipitation and radiation transfer, which cannot be resolved on a model scale. The development of such parameterisations is based on detailed observation and high-resolution process model studies (www.mpimet.mpg.de/wissenschaft). The finer the employed calculation grid in the climate models, the easier it is to directly calculate important smaller spatial processes which otherwise would fall through the "loopholes" and could be included in the calculations only as parameters (Böttinger, 2004) (Fig. 8.3). Current models, like ECHAM5 of the Hamburg MPI-M, have a resolution of less than 200 km (T63). 100

Fig. 8.3: Typical resolutions of current climate models with a grid width of around 500 km (T21), around 250 km (T42), 180 km (T63), and 110 km (T 106). T21 depicts the continental contour only very roughly. It is not possible to calculate the climate with this resolution, but the T42 models also only allow a limited calculation (MPI-M, Hamburg).

GCM models combine the basic physical laws (like conservation of momentum, mass and energy, radiation equation, gas laws) in the form of differential equations and calculate the most important atmospheric processes and state variables for each grid point. Depending on the starting and boundary conditions, an extensive system of differential equations must be applied for, e.g. solar insolation, topography of the terrestrial surface and albedo. Since it is impossible to solve these equations exactly (there is no known analytical solution), numerical approximation methods with iterative approximation to the respective solution have to be applied which requires an intense process of calculation. In order to calibrate these models, extensive tests are carried out. In addition to tests for individual components like atmosphere, sea and land, tests are also carried out for the coupled system in order to detect trends towards unrealistic states. It is important to validate them by recalculating the climate of the past centuries and by comparing them to the climate as it is actually observed. Despite all the uncertainties that still exist, it is meanwhile possible to reach quite a good agreement between the climate calculations from the model simulations (control runs) and the historically reconstructed climate. 101

Fig. 8.4: Schematic representation of an earth system model and its components (physical climate system (WCRP: World Climate Research Project), biogeochemical climate system (IGBP: International Geosphere - Biosphere Program), Human activities (IHDP: International Human Dimensions Program) (Cubasch 2002 and www.ucar.edu/)

8.1.2 Earth System Models Since 1990, important improvements have been obtained for the inclusion of further climate system components. While pure climate models (GCMs, AOGCMs) nearly exclusively consider physical processes in the atmosphere or sea, further developed climate system models also consider biological and geochemical interaction systems. The carbon circulation or other substance circulations, dynamic changes of kinds of vegetation, and the atmospheric chemistry are some of the processes, which at present are included in the existing circulation models. The earth system model (Fig. 8.4) strives to consider and model possibly all components of the climate system, accordingly also the biological and chemical processes in the sea and atmosphere, including their feedback and external disturbances. The models of all involved subsystems are coupled - that is, they exchange information at regular intervals – and thus form a simplified "earth system in a high-performance computer" (Böttinger 2004). With them, it is also planned to represent future consequences for e.g. marine and terrestrial ecosystems and their feedback on human societies (Cubasch 2003). This requires huge calculation capacities which only few computers in the world are able to perform. In mid 2006, with 280 tera flops, Blue Gene L in California was the quickest supercomputer of the world. Meanwhile, 13 different worldwide modelling groups have developed earth system models of intermediate complexity (EMIC). They use models of intermediate complexity for atmosphere and sea, but include additional processes like the carbon circulation and feedback on vegetation. The models are discussed and compared in regular workshops, and sensitivity studies are carried out (www.pik-potsdam.de/emics/toe_05-06-07.pdf). As there are still many processes which are represented only inadequately in climate models (e.g. clouds and convec- tive processes, precipitation, eddies in the sea), ensembles of several integrated models are designed to help quantify these uncertainties. To this end, the EU-supported PRISM Project (Program for Integrated Earth System Modelling) was developed (Brasseur 2003). In the course of ensemble calculations, model calculations are repeated several thousand times each time with slight variations of the initial values, in order to be able to separate random 102 results better from statistically secured trends (Böttinger 2004). Also the parameterisations of the model are changed according to this pattern. Accordingly, the higher the number of conducted model runs, the better the basis for the statistical evaluation of the ensembles. Addi- tionally, for the further development of earth system models, the European Network for Earth System Modelling (ENES – www.enes.org) was established with the help of the EU. When simulating the future climate by using e.g. greenhouse gas scenarios, a climate model is calculated long enough until there is no further significant change in the statistics of the climate elements. The state of balance found in this way, is called a climate signal and represents the difference between the climate statistics with disturbances which are due to the increased greenhouse gas concentrations, and the so-called climate noise, the statistics without disturbances. It is assumed that climate noise represents the natural variability of the climate.

8.1.3 Uncertainties in the Climate Model Calculations In addition to system-inherent uncertainties, the climate noise (see above), which derives from non-linear changes and instabilities of the climate dynamics, there is another uncertainty due to the insufficient knowledge of the system. Therefore, the complex coupled circulation models are also affected by uncertainties (Min 2006). Notwithstanding significant progress in the development of climate models, climate simulations are subject to numerous problems which should be taken into account at the time of evaluating their results. The potential of the computer systems employed is indeed growing at an enormous pace - the Japanese "Earth Simulator“ attains a maximum speed of 40 tera flops (40 billion operations per second). Nevertheless, numerous processes in the real climate and their changes have to be left unconsidered. At any one time it is possible to describe only partial aspects of the climate system and their changes which are based on certain disturbances. On the one hand, a reason for it is the limited potential of the models themselves, and on the other hand it is the observed data and other inputs originating from reality which are used for operating the models (changed, according to Kasang HBS 2005). Also von Storch (2005) states that the global climate models are subject to (relatively small) systematic errors and are capable only of describing part of the reality. Therefore, a climate change is derived from the difference between a "control run" (in which the composition is pre-defined with a changed time pattern) and a "scenario run" (for which the composition definition is changed at certain intervals) (von Storch 2005). Also according to Meehl (2005), the more recent models still contain some systematic errors. According to Edwards (2002), circulation models will contain semi-empirical values (parameters) and equations also in the foreseeable future. Despite all progress made in the past years in the development of models and large-capacity computers, parameterisation will continue to be carried out as small-scale processes cannot be represented by the rough grids of the circulation models. This applies to clouds, activities at the planetary boundary layer and factors which refer to the land surface, e.g. roughness and altitude above sea level. According to Bengtsson (2004), the coupling of atmosphere and ocean constitutes a special problem. Small changes in clouds and sea ice dramatically influence the exchange of energy and water. At the time of the model coupling, the observation data is replaced by the respective data of the other model system (Fig. 8.5). This creates errors in the heat, water and impulse flows which may result in significant deviations from the observed climate. This problem, which is called "climate drift", is corrected by a so-called "flux correction" which is a non- physical adaptation to reality. Accordingly, the flux of heat, fresh water and wind between atmosphere and sea are "flux-corrected" in terms of space and time in such a way that a climate drift is avoided, that means the flux correction is derived from the difference between the model flows and those which are necessary to adapt the model climate to the real one. Therefore, "flux correction" does not mean that the real flows, which are unknown, are entered in the model. More recent and complicated model developments, like the Hamburg ECHAM5/MPI-OM Model (see chapter 8.2.3) and most of the AR4 models, operate without these flux corrections and show a significant improvement compared to those models with 103 flux correction (Schnur 2003, Bengtsson 2004). Nevertheless, they are not free of errors either. Improvements were achieved in particular for heat flows.

Fig. 8.5: Ocean and atmospheric model are first of all started in a separate mode and define the boundary conditions of the other system by means of the real ocean and the real atmosphere (left). After having coupled both systems, it is necessary to carry out a flux correction in order to avoid a climate drift (right) (Kasang, HBS 2005)

In order to reduce the uncertainties of the model results, in 1995 the Coupled Model Inter- comparison Project (CMIP) was established (Meehl 2005). In it, among others, homogenous model calculations were carried out by all the participating model groups with an annual global average CO2 increase of 1 %. After a 70-year running time - which is the time it takes for the CO2 amount to double –, the results of the 12 model groups vary greatly by the factor 2 and lie between 1 and 3 °C. For precipitation, this difference is even bigger (Bader 2004). A good correlation was found after having defined the average of the multi-model ensemble. This is true also for ENSO and NAO. Systematic errors concerning the sea surface temperature and precipitation continue to exist for the Inner Tropic Convergence Zone (ITC) in the Pacific and for the Atlantic with the Southern hemispherical anticyclone, which is represented too weakly (Davey 2001). Big differences exist for the Polar regions, particularly due to a differing consideration of climate feedbacks in the model calculations for AR4; the deviations for the year 2100 are 1.3 to 4 times higher than the global average value (Bony 2006). Another model problem is the "cold bias“. This describes the temperature in the area of the extra tropical tropopause, which is systematically simulated several K too low by the global climate models. Sausen (2004) showed in an experiment carried out within the DEKLIM project COBI, that the cold bias is strongly influenced by the erroneous temperature distribution in the model. By using a higher resolution in the climate models, the cold bias could be significantly reduced. One of the biggest uncertainty factors in climate simulations is the influence of clouds because they can have both a cooling or warming effect. On the one hand, they absorb solar radiation (high clouds) and reflect it (the albedo is increased), which results in a negative radiative forcing. On the other hand, they (low clouds) can absorb long-wave infrared radiation and re-emit it (the greenhouse effect is enhanced), which results in a positive radiative forcing. Therefore, it is difficult to correctly integrate the effect of clouds in climate models. This is also shown by a model comparison by Soden (2006), according to which the feedback of the clouds continues to be the biggest source of uncertainty in the model calculations. There is by no means such detailed understanding of the manifold interactions of clouds as would allow their being exactly reconstructed in numerical models (Raschke 2002, Bony 2006). The global average is a 50 % cloud coverage of the earth. The climate effects of clouds derive from their radiative properties, their water and ice content (latently retained warmth), their production of precipitation, the dynamics of the atmosphere which is linked to their convection, and the processes which take place within them. Another uncertainty for the 104 inclusion of clouds in the climate models is the altitude of clouds, the precipitation amounts and the precipitation frequency. The aerosols (indirect effect) are another important influencing factor on the cloud formation. Certain aerosols can systematically reduce the size of particles in clouds, which increases their albedo and reduces the precipitation efficiency. As Schmidt (2006) reported, the improved GISS model of NASA, which was used for the simulations for the AR4 Report, also continues to have problems with the cloud coverage, particularly for the marine stratocumulus. The uncertainties of the Hamburg climate model ECHAM5 are referred to at the end of chapter 8.2.3. In contrast thereto, measurements of the increase of the moisture content in the upper troposphere, carried out by von Soden (2005), have confirmed the predictions of the climate models. Analyses of the water absorption bands of 6.3 µm with microwave spectrometers of satellite measurements in the period between 1982 and 2004, and the comparison with model calculations have shown a very good correlation. The increase of air humidity amounted to around 2 % and is considered to be the water vapour feedback as a result of the terrestrial warming. With this, another uncertainty factor of the climate models was eliminated. Another uncertainty is the evaluation of future emissions, as carried out by IPCC. Corre- sponding projections in climate models are partly based on the extrapolation of the trends of past decades (+ 1 % per year for the "equivalent" CO2), although it has to be taken into account that the increase has been smaller since the beginning of the 1990s and was nearer to 0.5 % per year. Future methane concentrations for example, are very difficult to assess, because of insufficient knowledge about the strength of sources and sinks (Bengtsson, 2004) (see chapter 6.1.3). 8.2 Results of Model Calculations The IPCC reports 2001 and 2007 published the model results of the participating model calculation groups. Using a model of average climate sensitivity, temperature projections were made for the six standard SRES scenarios and the "business as usual“scenario of the IPCC report (IS92a) for the period between 1990 and 2100. Some of the results are dealt with in chapter 8.2.2 and 8.2.3.

8.2.1 Emission Scenarios In order to assess the future climate on a realistic basis, in addition to the knowledge about the internal dynamics of the climate system, it is also necessary to know about the development of future natural and anthropogenic forcings. To this end, IPCC developed varying scenarios based on different assumptions of the development of mankind. The important factors are, in addition to the development of the global population, its standard of living, the energy consumption, the energy sources used for it and the efficiency of energy usage. From these factors result the emissions and environmental changes to be expected. The emission scenarios which were designed in a special IPCC report (SRES), are to cover the whole range of economically plausible future developments (Fig. 8.6). - Scenario A1 is based on a world with a quick economic growth and the quick introduction of new and efficient technologies. The CO2 and SO2 emissions start to decrease from the middle of the century. - Scenario A2 depicts a very heterogeneous world with a focus on traditional values. CO2 emissions continue to increase. After a strong increase, SO2 clearly decreases after 2050. - Scenario B1 describes a world which turns away from materialism, linked to the introduction of clean technologies. CO2 emissions increase slowly until around 2070, then they decrease. SO2 emissions decrease continuously. - Scenario B2 focuses on local solutions for economic and ecological sustainability. CO2 emissions continue to increase moderately, SO2 emissions slowly decrease.

105

Fig. 8.6: Overview of the four scenarios of the IPCC Report 2001/2007, together with the older "business as usual“ scenario of the 1992 report. The two graphs show the predicted trend each for the global carbon dioxide (upper right) and sulphur dioxide emissions (lower right) by the year 2100. These emissions strongly determine the anthropogenic influence on the climate and are directly included in the model calculations of the climate models (Kasang, HBS 2005, according to IPCC 2001)

There have been some controversies about the prognoses of the economic growth rates and the employed emission scenarios. Particularly the AF1 scenario with a quadrupled CO2 emission, which is based on a far-reaching combustion of the fossil energy reserves and which is said to lead to an extreme temperature increase of around 5.8 °C, is considered to be unrealistic. Also in the case of the IPCC scenario with the lowest amount of accumulated emissions and the smallest temperature increase, in 2100, the growth of the gross national product per inhabitant in the Asian states is said to be 70 times higher than in 1990 and nearly 30 times higher in the remaining developing countries. The assumption which is based on this scenario and which states that the economies of the poor developing countries will catch up relatively quickly with those of the rich countries, is considered to be unrealistic e.g. by Castles and Henderson (2003, 2005). Another disputed point of criticism was the fact that the market exchange rate (MEX) was taken as the basis for the economic change as expected, but not the purchasing power parity (PPP) (Tol 2004, Lawson 2005). The temperature differences resulting from this, however, amount to a mere 0.1 °C for the year 2100. Also for the power generation in the developing countries, the assumed growth is said to be too high, compared to the IEA prognoses. While IEA states a factor of 3.2 by 2030, the IPCC scenario is based on a factor of 5.5. Therefore, it is assumed that the emission scenarios are assessed at too high a level. Tol 2005 compared the SRES scenarios with more recent ones and did not find any major discrepancies. In various workshops, IPCC has discussed the criticisms and rejected them in parts. The Electrical Power Research Institute (EPRI), USA, for instance, carried out calculations with MEX and PPP which showed only small deviations (IPCC 2003, Manne et al 2005). In an extensive study, also Nakicenovic (2003) rejects the criticisms in detail. The 4th IPCC Report will again be based on the previous emission scenarios, but the criticisms will be taken into consideration. The various scenarios of the IEA, the EEA and OECD will be assessed, and peer-reviewed scientific publications (IPCC Expert Meeting on Emission Scenarios 2005) will be taken into account. New emission scenarios, which consider the criticisms of the econo- mists, are to be drawn up for the 5th IPCC Report in 2013 (Schiermeier 2006). For the period 106 until 2030, IIASA (2006) calculated new emission scenarios for some direct and indirect greenhouse gases, and partly significant deviations from the SRES scenarios were found for CH4, NOx, CO and SO2. The emission scenarios lead to carbon dioxide concentrations (Fig. 8.7) between 540 and 970 ppm, which are used in the model calculations (chapter 8.2.2).

Fig. 8.7: Scenarios of the anthropogenic CO2 emissions and the atmospheric carbon dioxide concentration for the six exemplary scenarios of IPCC 2001 and the "business as usual" scenario (IS92a) of IPCC 1996 (Kasang, HBS 2005, according to IPCC 2001)

8.2.2 Climate Projections for TAR (2001) - Model Results By means of the emission scenarios, the climate models allow to estimate what kind of climate changes these possible future emissions could have. Due to the fact that the employed scenarios are based on various assumptions and therefore are no prognosis, the model results are called projections. In the model calculations, the climate change is derived from the difference between a control run with a "real climate" and a scenario run. According to the varying scenarios, the carbon dioxide concentrations amount to between 540 and 960 ppm for 2100, with an annual carbon dioxide emission of between 5 and 29 billion t. The climate projections with their 35 different emission scenarios predict an increase of the average global air temperature near ground level of 1.4 to 5.8 °C by the end of this century. The enormous range of the temperature prognoses is on the one hand rooted in the uncertainty of the climate model calculations, and on the other hand in the big differences of the emission scenarios which were taken as the basis (Fig. 8.8). The range of eight employed model results for the emission scenario A2 in the year 2100 accordingly varies by more than factor 2. The grey graph, which is labelled "all model results", shows the whole range of the results, if all 35 SRES scenarios, all the different models and the uncertainties are taken into account. Nearly everywhere, the temperatures will increase all over the globe (Fig. 8.11). Owing to its thermal inertia, the increase will be slowed down a little above the sea; in the Arctic regions, the temperature rise will be significant after permafrost and sea ice will have melted away there (von Storch 2006). 107 .

Fig. 8.8: Temperature scenarios according to the IPCC 2001 emission scenarios, with indications of existing uncertainties. For 2100, an average global temperature rise of between 1.4 and 5.8 °C will be the result, compared to 1990 (IPCC 2001)

8.2.3 Climate Projections for AR4 (2007) - Model Results 17 modelling groups from 10 countries have contributed to the 4th IPCC Report (AR4) with 23 models. The model data – 27 tera bytes - are collected, archived and put at the experts' disposal by the PCMDI (Program for Climate Model Diagnosis and Intercomparison). The results of the model calculations, which are included in AR4, were peer-reviewed in over 200 papers which were published in specialised journals (www.ipcc.ch). According to IPCC 2007, a major advance of this assessment of climate change projections in AR4 compared with the TAR is the large number of simulations available from a broader range of models. Taken together with additional information from observations, these provide a quantitative basis for estimating likelihoods for many aspects of future climate change.

Model projections based on analysis of the different computer climate models running within different SRES scenarios predict during the 21st century following surface air warming:

9 Best estimate for a "low scenario" is 1.8 °C with a likely range of 1.1 to 2.9 °C 9 Best estimate for a "high scenario" is 4.0 °C with a likely range of 2.4 to 6.4 °C 9 A temperature rise of about 0.1 °C per decade would be expected for the next two decades, even if greenhouse gas and aerosol concentrations were kept at year 2000 levels. 9 A temperature rise of about 0.2 °C per decade is projected for the next two decades for all SRES scenarios. Confidence in these near-term projections is strengthened because of the agreement between past model projections and actual observed temperature increases. Advances in climate change modelling now enable best estimates and likely assessed uncertainty ranges to be given for projected warming for different emission scenarios. Results for 108 different emission scenarios are provided explicitly in this report to avoid loss of this policy- relevant information. Projected globally-averaged surface warmings for the end of the 21st century (2090–2099) relative to 1980–1999 are shown in Fig. 8.9. These illustrate the differences between lower to higher SRES emission scenarios and the projected warming uncertainty associated with these scenarios (SPM, IPCC 2007).

Fig. 8.9: Solid lines are multi-model global averages of surface warming (relative to 1980-99) for the scenarios A2, A1B and B1, shown as continuations of the 20th century simulations. Shading denotes the plus/minus one standard deviation range of individual model annual averages. The orange line is for the experiment where concentrations were held constant at year 2000 values. The gray bars at right indicate the best estimate (solid line within each bar) and the likely range assessed for the six SRES marker scenarios. The assessment of the best estimate and likely ranges in the gray bars includes the AOGCMs in the left part of the figure, as well as results from a hierarchy of independent models and observational constraints (SPM, IPCC 2007)

For the model calculations of the MPI-M, carried out for the 4th IPCC Report 2007 (AR4), the coupled atmosphere/ocean/sea ice/continental surface model ECHAM5/MPI-OM was used, which was newly developed at the MPI-M. According to indications of MPI-M, the calculations were carried out with the 1.5 tera flops NEC SX-6 vector computer which is the quickest European supercomputer for climate research at present. Thousands of processors calculated at record speed of 1.4 trillion computer operations per second (tera flops). The Hamburg MPI-M 2006 states in its brochure (2006) the following uncertainties concerning its climate prognoses: - future emissions, - natural climate fluctuations which superimpose anthropogenic trends, - a rough calculation grid of around 200 km, - calculation of those processes which cannot be resolved by the calculation grid, - missing processes like e.g. biochemical circulations. The British Hadley Centre found similar model results in its model calculations for AR4. In 2005, Hansen published model results according to which the earth currently absorbs 0.85 109 W/m2 more solar energy than it reflects. This imbalance is confirmed by exact measurements in the sea (Novakov, 2005). Consequently, the temperature will additionally increase by 0.6 °C also if there are no further changes in the atmospheric carbon dioxide concentrations.

8.2.4 Regional Model Results Local climate change is influenced greatly by local features such as mountains, which are not well represented in global models because of their coarse resolution. As global climate models calculate only statistical average values and their changes over decades and centuries, a downscaling has to be applied for regional considerations. Regional climate models focus on one section of the earth, and therefore, they need adequate boundary conditions for the boundaries of the model region. These boundaries are taken from scenarios of the global climate models. Therefore, it is said that a regional climate model is driven by a global climate model. This is called "dynamic downscaling", a term which describes the downscaling of global forcing data until a very fine regional resolution is obtained (up to one kilometre grid width) (Matula 2003).

Fig. 8.10: From a global to a regional and local climate model by means of dynamic downscaling (Kasang, HBS 2005)

For the dynamic downscaling (Fig. 8.10), high-resolution models for individual regions are embedded in a rough global model, using the data of the global model as boundary conditions. According to the same principles, a local model may be embedded in a regional model. If an empirical/statistical downscaling is performed, a statistical relation between regional or local climate variables, e.g. for temperature and precipitation, and large-scale conditions (e.g. circulation patterns) are derived from observations. Then, these relations are applied to the results of the global coupled models in order to establish local and regional climate properties (Cubasch u. Kasang 2002; Matulla 2002). Projected warming in the 21st century shows scenario-independent geographical patterns similar to those observed over the past several decades. Warming is expected to be greatest over land and at most high northern latitudes, and least over the Southern Ocean and parts of the North Atlantic ocean (Figure 8.11). 110

Fig. 8.11: Projected surface temperature changes for the early and late 21st century relative to the period 1980– 1999. The central and right panels show the Atmosphere-Ocean General Circulation multi-Model average projections for the B1 (top), A1B (middle) and A2 (bottom) SRES scenarios averaged over decades 2020–2029 (centre) and 2090– 2099 (right). The left panel shows corresponding uncertainties as the relative probabilities of estimated global average warming from several different AOGCM and EMICs studies for the same periods. Some studies present results only for a subset of the SRES scenarios, or for various model versions. Therefore the difference in the number of curves, shown in the left hand panels, is due only to differences in the availability of results (SPM, IPCC 2007).

On 25 April 2006 (UBA 2006), the Hamburg MPI-M presented to the public the results of its "Regional Projections for the 21st century". Employing the regional climate model REMO, climate change simulations were carried out with a grid width of 10 x 10 km for Germany, Austria and Switzerland.

Fig. 8.12: Chronological trend of the simulated air temperature (°C) in Germany for the three emission scenarios of IPCC (A1B, B1, A2) for the period between 2000 and 2100 (www.umweltbundesamt.de/uba-info- presse/hintergrund/Klimaaenderungsworkshop.pdf)

111 Depending on the amount of future greenhouse gas concentrations, temperature increases of an average of 2.5 to 3.5 °C are expected for 2100 according to the above-mentioned calculations (Fig. 8.12). Regionally different temperature increases of up to 5 °C may occur in the Alpes, and of 3 °C at the Baltic Sea. The summers in the South, Southwest and North- east of Germany will probably become more arid. The total amount of precipitation will most probably not change, but in the mountains in the South of Germany, precipitation will increase by around one third in winter. A new regional model study for Germany (WETREG) published by UBA on February 2007 shows similar but smaller results with regional differences compared to the REMO model results (http://www.umweltbundesamt.de/uba-info-presse/hintergrund/ Regionale- Klimaaenderungen.pdf). According to this study, end of the 21st century the average temperature could rise 1.8 to 2.3°C. Uncertainty in the impacts of regional climate change comes from many sources, not least the downscaling methodology, model and emissions scenario chosen. Ensemble experiments demonstrate that the predictability of the regional climate varies strongly (Vidale 2003). Uncertainty due to internal variability become greater as spatial scale reduces from. the global scale to continental scales (Stott 2003). Differences in projections of regional temperature are smaller than precipitation changes by different models.

8.2.5 Detection of the Greenhouse Effect - Influencing Factors on Model Calculations By means of climate model calculations, it is tried to identify causes for the climate changes which have happened after 1850, and to simultaneously test the models by means of climate observations. In order to get realistic results from model calculations, all influencing factors on the climate system have to be taken into account (Fig. 8.13).

Fig. 8.13: External (natural (solar radiation, volcanos) and anthropogenic (greenhouse gas emissions)) and internal influencing factors on the climate system produce climate change (Kasang, HBS 2005) To this end, several climate experiments were carried out (Cubasch 2003), which are shown in Fig. 8.14. In a first experiment, only natural forcings and their fluctuations (solar variability and volcanism) were considered, in a second only the anthropogenic ones (greenhouse gases and sulphate aerosols), and in a third experiment, the combination of natural and anthropogenic forcings was tested. The blue graph represents the model calculations, including their uncertainties, the red one the observed temperature trend. As can be seen in Fig. a), fluctuations of the solar insolation are responsible for several tenths of degrees of the temperature increase. But also anthropogenic changes (Fig. b) are not sufficient data for a simulation of the temperature increase by means of a model. Figure c) shows that only the consideration of all forcings obtains a good correlation with the observations. 112

Fig. 8.14: Results of climate model calculations which consider various natural and anthropogenic influencing factors (IPCC 2001, Cubasch 2003)

According to Cubasch (2003), the results as they are represented here, show that the climate models are able to reproduce the observed temperature trend of the 20th century in good approximation, if the most important anthropogenic influencing factors like greenhouse gases and sulphate aerosols are taken into account. According to Roeckner (2002, 2004), this does not only apply to the average global temperature, but also to the Arctic ice extension and the heat content of the big oceanic basins. In his study, Stott (2001) confirmed that anthropogenically caused changes in the concentration of greenhouse gases, sulphate aerosols and ozone may explain the climate warming since 1975, but not the warming in the first part of the last century and the subsequent cooling (Schnur 2003). Stott 2003 assumes that the present climate models underestimate the temperature changes due to weak signals, like changes of the solar radiation. As a result, he found a bigger influence of the change in solar insolation on the average global temperature in the first half of the past century. By means of model calculations of the Hadley Centre, GB, Stott 2003 proves in another study that there is an anthropogenic contribution to the climate warming in the 20th century in six different regions of the earth like Europe, America and Asia. By means of model comparisons, Stott 2006 shows that the temperature trend in the 20th century is represented relatively well if the natural and anthropogenic forcings, including the aerosols, are taken to form the basis. All three models show the cooling effect of aerosols. The climate-modelling members of the NASA Goddard Institute (Hansen 2005a) have used the best estimations of the climate forcings since 1880 for their climate model (GISS), and they simulated the temperature trend until 2003 (Fig. 8.15). The sporadic cooling effect of volcanic aerosols is as clearly shown as the small positive trend of the solar forcing. The simulation calculations also correlated quite well with the observed temperature trend. This is 113 considered to be further evidence for the fact that current climate models correctly simulate the temperature trend, although there might be some discrepancies in the spatial distribution.

Fig. 8.15: Model calculations of the Goddard Institute with (A) climate forcings used for the climate simulations, and (B) the temperature change simulated with the GISS model and actually observed for the period between 1880 and 2003 (Hansen 2005a)

Also the so-called fingerprint method, which examines the varying spatial warming pattern caused by changes in the solar insolation or anthropogenic influences, has shown a clear preponderance of anthropogenic patterns in the last decades. The greenhouse effect produces a different vertical and horizontal warming pattern (particularly high in high latitudes and above the continents) than an increased solar insolation (Kaminski and Cubasch 2003). According to Santer (2003), the observed increased elevation of the tropopause by some 100 m is another "fingerprint“ of the anthropogenic contribution to the climate warming. The observed temperature increase mainly in winter and at night also corresponds to the theoretical expectations (UBA 2004). From 1979 to 2004 both day- and night-time temperature have risen at about the same rate. The trends are highly variable from one region to another (SPM, IPCC 2007). The distribution of the ocean warming measured by Barnett 2005 is also considered to be a proof ("smoking gun“) for the anthropogenic greenhouse effect (see chapter 9.5.1). A study (Rahmstorf 2006), which was performed at the end of the 1990s, showed that the temperature trend until 1940 might be explained by a combination of greenhouse gases and internal variability, and partly by an increase of the solar activity. The further course between 1940 and 1970 is derived from the superposition of the cooling effect of the aerosols and the 114 warming effect of the greenhouse gases. By means of empirical-statistical analyses, Grieser 2000 establishes a highly significant context between the increase in greenhouse gases and the increase of the average global temperature. This is not so clear for Europe, because here, the NAO influence prevails. After having performed statistical analyses of temperature/time series, also Rybski 2006 found that the greenhouse gases must have played a role in the warming of the 20th century. Rahmstorf 2007 found good agreement between model projections for the TAR and the observed trends of CO2 concentration, gobal average temperature and sea-level rise since 1990. The equilibrium climate sensitivity is a measure of the climate system response to sustained radiative forcing. It is not a projection but is defined as the global average surface warming following a doubling of carbon dioxide concentrations in degrees Celsius per radiation unit (°C/W/m2)). It is likely to be in the range of 2 °C – 4.5 °C, with a best estimate of about 3°C and was repeatedly confirmed by many model studies, and also the 4th Report of IPCC considers it to be the most probable value (SPM, IPCC 2007). The direct warming due to the radiation effect with a doubled carbon dioxide amount results in 1.2 °C. To this end, the feedback by water vapour, ice albedo and clouds has to be taken into account. The largest uncertainty remains in the insufficient knowledge of the feedback of clouds. To this end, extensive measuring programmes are being carried out at present (Rahmstorf 2006). Kuzmina (2005) compared the results of 12 coupled climate models, which participated in the model-comparing project (CMIP2), with data from observations. The majority of the models shows a significant trend towards an enhanced NAO, if the greenhouse gas concentrations increase. Current models represent climate effects of volcanic eruptions correctly. Upshot: Many examinations carried out by climate scientists with different methods confirm that the climate warming of the last 50 years has, among others, substantially been caused by anthropogenic factors (SPM, IPCC 2007). 115

9 Impacts of Climate Change Statements about changes of global average values alone do not yet offer any indications about the impact a climate change could have on nature and mankind. Climate changes may cause positive as well as negative effects on man and nature in different regions.

Fig. 9.1: Map of the world with tipping points for which possible climate effects are discussed (Schellnhuber, Rahmstorf 2006)

Figure 9.1 shows a map of the world according to Schellnhuber (2005), indicating critical regions (tipping points) for which possible climate impacts are being discussed. Tipping points shall help to focus on regions, where sudden short-term events could occur in at least subcontinental dimensions, mainly triggered by an anthropogenic climate warming. Among these are the instability of the Greenland ice sheet, the Amazonas rain forest, thawing of permafrost, the Asian summer monsoon and others. A positive effect could be a newly vegetated Sahel, and also changes in the summer monsoons could partly lead to positive effects. In order to be able to assess climate effects, a very differentiated approach is necessary. In many regions, higher temperatures are favourable for agriculture and crop yields - as long as there is enough water for irrigation. In other regions, a temperature rise causes more droughts and reduces the crop yield. An ice-free Arctic region is favourable for navigation which would considerably shorten the sea routes, but the albedo would change considerably, with the respective climate effects. Warmer winters reduce the number of heating days, but in hot summers, the increasing use of air conditioning systems will augment energy consumption. 116 9.1 Temperature Extremes Extreme events are understood to be rare weather events and natural phenomena strongly deviating from the average. Extreme events may cause major damages. At present, scientists discuss whether the observed climate change could result in an increase in extreme events. Based upon pure statistical considerations, it must be assumed that an increase of the average temperature will cause a rise in the number of hot days (IPCC 2007, Graßl 2003) (Fig. 9.2).

Fig. 9.2: If the average climate shifts towards a warmer state, the frequency of extreme periods will shift as well. There will hardly be any cold periods, hot periods will be more frequent and even hotter (IPCC 2007).

Accordingly, one consequence of climate change could be higher temperature extremes. It is expected that such heat waves will cause reduced crop yields and result in additional death cases. An example is the extremely hot summer in 2003, which in Germany alone caused around 3,500 deaths attributable to heat - in Europe, more than 20,000 (Schär 2004). On the other hand, it has to be taken into account that an evaluation of various heat waves showed fatalities to drop below the average experienced value ("harvesting effect") after the heat wave was over. This means that during a heat wave a part of the increased mortality occurs some days earlier. Yet, epidemiological studies also revealed death cases which were not to be expected within the following weeks without the impact of heat (Munich Re Group 2004), i.e. an actual increase in mortality also existing over a long period. Stott 2004 concluded that more than half of the risk for hot summers such as the one in 2003 is attributable to anthropogenic influences (probability of error 10 %). After having carried out model calculations, Meehl (2004) states that in the 2nd half of the 21st century, heat waves will be more frequent in Europe and USA. Dai 2004 established that the share of very arid areas in the global land surface has increased from 12 to 30 % since the 1970s (Fig. 9.3). Eurasia, Africa, Canada, Alaska and Eastern Australia have become more arid since the 1950s, and Argentina, the Southern parts of USA and Western Australia have experienced enhanced precipitation during the same period. 117

Fig. 9.3: The share of very arid regions in the global land surface (60 S - 75 N) between 1950 and 2002. A clear increase since the 1970s (Kasang 2005), according to Dai (2004))

A study carried out by the PIK (Zebisch 2005) shows an increase of heat extremes for Ger- many during the last 100 years.

9.2 Precipitation, Floods On a warmer earth, the total amount of precipitation will increase, because more water evaporates and the atmosphere is able to retain more water. According to model simulations, precipitation will enhance mainly above landmasses (Roeckner 2004). This leads to an in- tensification of the water circulation, and the probability of heavy precipitation will increase (Fig. 9.4). The understanding of this process, and model calculations, too, lead to the assumption that the intensity of heavy precipitation and floods will enhance. According to Alex- ander (2006), heavy precipitation has globally increased in the 20th century.

Fig. 9.4: Schematic representation of the greenhouse effect: rise of temperature leads to an increased water vapour content in the atmosphere and more evaporation. The consequences are more droughts in some regions, and heavier precipitation in others (Kasang, HBS 2005)

After the disastrous flood of the river Elbe in 2002, Muddelsee (2003) evaluated the historic flood data of the Elbe and Oder rivers but could not find any significant increase of flood fre- 118 quencies for the past 80 and 150 years, whereas the water level of the Rhine in Cologne shows an upward trend, although with significant fluctuations (Jonas, 2005). In an extensive study carried out for the KLIWA project, Caspary 2004 found out that since the 1970s, the flood water levels (90 water levels) have increased in Southern Germany. Even if the statements about an intensified water circulation are true for the global average, the evaluation of flood data shows that other influencing factors may be more essential for individual regions. The spatial distribution of precipitation is closely connected to the horizontal and particularly vertical movements in the atmosphere. Therefore, weather conditions with their specific circulation patterns are an important influencing factor on precipitation. Thus, the change of certain weather situations may influence heavy precipitation (Fricke 2002). An analysis of Hohenpeißenberg in Bavaria showed that the increase in the number of days with heavy precipitation coincides with an augmentation of extended-range weather situations, during which heavy precipitation is frequent. A Germany-wide analysis of heavy precipitation in the period between 1901 or 1951 and 2000 shows an increase in heavy precipitation and its intensity. In winter, higher and more significant trend increases occurred (30-35 %) than in summer (Zimmermann, DWD 2002, Schönwiese 2005c). Jonas, Schönwiese (2005b) have found changes in frequency and intensity of extreme events in Central Europe, but they do not agree with the general statement that climate in Germany has overall become more extreme. Due to the temperature increase, the frequency of freezing days will probably decrease in the course of the climate change. As a consequence, less heating days ought to be necessary, and the energy consumption in the heating period will decrease, which in turn will lead to a reduced CO2 emission.

9.3 Storms and Hurricanes The discussion on a possible increase in storms and hurricanes is still in progress amongst experts and quite controversial in part. According to Munich Re Group, statistics on tropical cyclones in the North Atlantic and North West Pacific show an increase in storm activities for the period between 1950 and 2003. Yet, this increase could be stated only for weaker events. The average annual number of hurricanes and typhoons remained the same. The reasons for this increase are unclear. At least for the period after 1970, an improved observation due to the analysis of satellite images could be responsible for it. Additionally, the growth of maritime regions with a regional sea temperature increase to over 26 °C could play a role in the formation of tropical cyclones (Munich Re Group 2004).

9.3.1 Storms Weisse (2005) found a rise in storm activities in the Eastern North Atlantic and the North Sea for the period between 1958 and 2002, which, however, partly decreased again, or respectively the increase rate of which slowed down for the past years. Figure 9.5 clearly shows that since the beginning of the 1970s, the storm frequency has increased above the North Sea, but it also shows that around 1880, the situation was similar. Analyses of wind speeds and low air pressure values alike showed an above average frequency of storms and strong depressions above the North Atlantic in the 1990s. Due to the fact that a similar maximum occurred at the end of the 19th century, the current increase could also be a short-period oscillation of the climate system (Lefebvre 2003). Model calculations carried out within the PRUDENCE EU project showed that under future climate conditions, storm tide extremes at the North Sea coast could increase (Woth 2005, Barring 2004). Ulbrich (1999) calculated an increase of depression activities for North West Europe in the case of a carbon dioxide doubling (Fig. 9.6). Otte (2000) observed an increase of squalls over wind force 6 for some German stations in the period between 1969 and 1999. 119

Fig. 9.5: Storm frequency in the area of the North Sea, British Isles, Norwegian Sea (1881-2002); a storm indicator is dis- played, which is derived from the intra-annual percentile of geotropic wind. Updated version of the graph by Alex- andersson (2000) (from: von Storch 2005): No increase of the storm frequency in the 20th century

Fig. 9.6: According to model calculations, the graph shows the changes in depression activity (geopotentielle metres) above Northwest Europe in the case of the doubling of the CO2 concentration (Ulbrich 1999, Kasang, HBS 2005)

Von Storch (2005) and Woth (2005) calculated the storm tides to be expected for the Ger- man North Sea coast in 2070 and found an increase of around 70 cm in the case of a continued climate change. 30 to 40 cm are the result of elevated storm tide levels, and 20 to 40 cm are the result of thermal water expansion caused by higher temperatures and the ablation of parts of the Greenland ice shelf and Antarctica.

Current State of the Discussion The experts discuss whether the frequency and/or strength of storms will increase in future if the climate continues to warm up. Due to the fact that the expected stronger temperature increase in higher latitudes reduces the temperature gradient between Equator and Pole, storm activities should rather decrease. On the other hand, the temperature rise in the upper layers of the atmosphere caused by the greenhouse gases is more pronounced in the tropical regions than in the higher latitudes. More water vapour is released which condenses in high altitudes and releases latent heat energy. This results in an increase of the meridional temperature gradient, and the jet stream is enhanced. Consequently, in the lower tropo- 120 sphere there is a formation of rather less strong than many weaker depression vortexes and storms (Kasang, HBS 2005). Model calculations for the German North Sea coast carried out by von Storch (2005) resulted in an increase of storm tides (see above).

9.3.2 Hurricanes (Tropical Cyclones) Hurricane Katrina of September 2005 with its dramatic consequences for New Orleans and its surroundings has rekindled the discussion about a possible contribution of global warming with respect to the intensity and frequency of tropical cyclones. With 28 tropical cyclones, among them 15 hurricanes and 7 major hurricanes, the year 2005 produced the highest amount of tropical cyclones since the beginning of weather recording (noaa.gov) (Fig. 9.7). The Atlantic hurricane season 2006 was against the forecasts slightly under normal with 5 hurricanes and 2 major hurricanes. Probably due to a rapidly-forming El Niño event, combined with the pervasive presence of the Saharan Air Layer over the tropical Atlantic, contributed to all tropical cyclone activity ceasing after October 2. (http://hurricane.atmos.colostate.edu/Forecasts/2006/nov2006/nov2006.pdf) Decadal fluctuations of hurricane activities were already observed in the 1940s and 1950s. In the 1970s and 1980s, the hurricane activity clearly decreased. The reason for the decadal fluctuations is stated to be a corresponding fluctuation of the ocean temperature which is possibly connected to variations of the thermohaline circulation.

Fig. 9.7: Number of storms and hurricanes in the North Atlantic between 1944 and 2005 (Pachauri 2007)

What is a tropical cyclone? Everywhere in the tropical seas, tropical cyclones develop where the water is warm enough and other preconditions are met (Fig. 9.8, 9.9). Depending on the region where they occur, they have different names: they are called hurricane in America, the Atlantic and Eastern Pa- cific regions, they are called typhoon in the Northern West Pacific near Japan and China, cyclone in the Indian Ocean and off East Africa, and Willy-Willy in Australia. 121

Fig. 9.8: Development and structure of a hurricane (Kasang, HBS 2005) The preconditions for the development of a tropical cyclone are: - The water must have a minimum temperature of more than 26 °C. - The air must be very humid. - The sea needs to have a certain minimum size, like the Atlantic, the Pacific or Indian Ocean. - The high-altitude winds must not blow with a quite different pattern than the surface winds (e.g. no big shear winds). - A wave disturbance (Easterly Wave) or a non-tropical depression is necessary as starting mechanism. - The warm and humid air rises, and further air masses are drawn behind it. - Condensing air humidity forms thundery clouds and releases additional energy which enhances the rising air current. - High air pressure forces the risen air towards the outside. - The rotation of the Earth (Coriolis force) starts to spin the storm (clockwise in the North- ern hemisphere, and the opposite in the Southern hemisphere). - In the middle, a calm eye develops. Within it, strong up-currents circle upwards on its edges. - In the middle of the eye, the air is sucked downwards, and extremely low air pressure develops. Tropical cyclones may reach a diameter of more than 500 km, an altitude of 15 km and a velocity of over 250 km/h. The warmer the oceans, and the bigger the sea water regions, the more frequent and destructive hurricanes may be. This allows the assumption that a climate warming could lead to more frequent and stronger tropical cyclones.

Discussion about the anthropogenic influence The US-American scientists Emanuel (2005) and Webster (2005) gathered evidence for a possible anthropogenic influence. Webster studied the number, duration and intensity of tropical cyclones for the past 35 years (Fig. 9.7). With an increasing sea water surface temperature, number and share of hurricanes of the category 4 and 5 strongly increased. This is particularly true for the Northern Pacific, the Indian Ocean and the South West Pacific Ocean, but it is almost not applicable to the North Atlantic. 122

Fig. 9.9: Hurricane above Florida, USA (www.ncdc.noaa.gov/oa/climate/research/2005/hurricanes05.html) The evaluations of tropical cyclones since the middle of last century by Emanuel (2005) showed that the total amount of energy of the cyclones has significantly increased. In his so- called PDI index, Emanuel compiled data of the earth surface affected by the cyclone, wind speed, cyclone radius and duration. The result was unambiguous. The amount of energy which was released by North Atlantic and Southern Pacific cyclones has clearly increased since the 1970s. This is due to an increase of both, the duration of hurricanes and the maximum wind speeds in the Atlantic and Pacific by around 50 % in the last 50 years. According to Emanuel, this fact confirms the simulations, and he assumes that the hurricane energy is closely connected to the sea temperatures and that it reflects the climate warming. Other researchers do not go as far: They state that there is an increasing probability of the formation of hurricanes at higher sea temperatures, but a statistical connection cannot be confirmed yet (Prof. Gerstengarbe, PIK Potsdam, Welt 30. Aug. 2005). Munich Re Group is also very tentative in this respect (see above). Since the first half of the 1990s, there has been a clear increase in the strength of hurricanes, but in the 1950s and 1960s there was a comparable accumulation of strong hurricanes. Other climate scientists, like Bengtsson and Botzet of MPI-M Hamburg (2005) emphasise that a climate warming could also prevent hurricanes, because more movements could occur in higher altitudes, thereby enhancing shear winds and thus preventing either of the preconditions for the development of hurricanes. Emanuel (2005), Landsea (2005), Kerr (2005), Pielke (2005), Trenberth (2005) and others have concerned themselves with the various statements about the reason for the increase in hurricanes. A new study by Hoyos (2006) concludes that the increase of the surface temperature of the oceans in the tropical zone amounts to nearly one degree C for the period between 1970 and 2004, and that this is a "contributive element" to the increasing strength of hurricanes. The NOAA – the North American Weather Service - declared in a statement published on 29.Dec.2005 that hurricane scientists and meteorologists of the NOAA (but not all of them) assume that the present enhancement of hurricane activities primarily is the result of natural fluctuations in the tropical climate system (tropical multi-decadal signal). 123

9.4 Ice Glaciers and ice caps retain considerable bodies of water which correspond to a sea level equivalent of around 70 m (glaciers and smaller ice caps account for around 51 cm, Greenland ice approx. 7.2 m, Antarctic Ice Shelf about 61.1 m). The behaviour of these ice masses in the case of a global warming has a decisive influence on our climate. Due to a clearly lower surface temperature, the Antarctic should be considerably more stable (Greve 2003). If the sea level rose by around 5 m, countless near-coast flat countries with approximately 2 billion inhabitants would be affected. If the sea level rose by 1m, around 3 million people would be affected at the German coast.

9.4.1 Glaciers The increase and retreat of glaciers are above all natural processes which have frequently occurred in the past. Figures 9.10 and 9.11 show that the retreat of some glaciers already started before industrialisation. Between 1961 and 1990, the ablation of glaciers contributed to a sea level rise by a total of 0.25 mm/year (Dyurgerov 2002). The WGMS (World Glacier Monitoring Service) collects data of around 68,000 glaciers. Since 1946, a mass balance has been drawn up for approx. 300 glaciers (http://nsidc.org/data/glims/glaciermelt/index.html). Since 1986, the WGMS (www.wgms.ch) Zurich has been collecting worldwide data on the

Fig. 9.10: Annual change of the global glacier thickness (left axis m/year water equivalent) and accumulated value (right axis in m). The cooling effect due to volcanic eruptions with stratospheric aerosols is also clearly visible; red arrow: change of the volume change rate (source: Dyugerov, http://nsidc.org/data/glims/glaciermelt/index.html) behaviour of alpine glaciers. For decades, the majority of the studied glaciers (30 glaciers in 9 mountain areas around the globe) has clearly ablated. The loss of the average mass balance has clearly accelerated in the last years (Fig. 9.10), and the number of glaciers with an increase has dropped (10 % in 2002/03, compared to 32 % in the period between 1980 and 99). Since 1850, the glacial volume has decreased by an average of approx. 50 % in the Alps, and the glacial surfaces have been reduced by around 30 – 40 % in the same period (Haeberli 2005). The increase of the Franz Josef Glacier in New Zealand originates in the strong rise in precipitation in the last years. In Norway and New Zealand as well, growing glaciers were found (Fig. 9.11) (Chinn 2005). Therefore, forecasts on global changes are 124 only possible to a limited extent. Extensive measuring programmes of the big ice masses are carried out in the Antarctic region and in Greenland as well. They are destined to find out whether ablative or increasing processes by solid-formed precipitation are prevailing. Meanwhile, in the Alps the first glaciers are being covered with plastic foil in order to avoid further ablation in summer (parts of Gurschen Glacier near Andermatt, dpa, 10. May 2005). According to Bindschadler (2006), in both hemispheres, glacier discharge to the sea has increased markedly in recent years as warm water from intermediate depths is melting the floating ends of glaciers from below, accelerating them. The estimated contribution from glaciers and ice caps to the sea-level rise has accelerated: 1961- 2003 0.5 ± 0.18 mm/yr to 1993 - 2003 0.77 ±0.22 mm/yr (SPM, IPCC 2007).

Fig. 9.11: Changes of 20 glaciers around the globe (see map below). The box length (above) corresponds to 1 km (source: IPCC 2001, HBS 2005)

According to statistical evaluations of the simulation carried out with the climate model ECHAM4, the retreat of the alpine glaciers before 1900 is explained by Bengtsson (2004), like already by Reichert (2002) to be a process dominated by natural fluctuations, whereas 125 the one occurring in the 2nd half of the 20th century is most certainly attributable to anthropogenic effects (Bengtsson 2004). IPCC 2007 summarises: Mountain glaciers and snow cover have declined on average in both hemispheres. Widespread decreases in glaciers and ice caps have contributed to sea level rise (SPM, IPCC 2007).

9.4.2 Antarctica At present, the ice of the South Pole contains around 90 % of the global solid water. The Western Antarctic ice shelf holds 75 % of frozen fresh water, which represents over 3 million cubic kilometres. Should it ablate, the sea level would globally rise by 5 m. While experts agree that the ice sheet is relatively stable on the east side of the continent, they are not so sure about the future behaviour of the Western Antarctic ice mantle. Thus, it was feared that the ice flows might start to slide towards the Ross sea (Fig. 9.12). After all, in the past years, the ice sheet has thinned in a little sector (Amundsen Sector), and the majority of glaciers (87 %) has retreated (Alley 2005, Cook 2005). New measurements of changes in the gravi- tate from the Gravity Recovery and Climate Experiment (GRACE) satellites have determined a mass loss in particular for the Western Antarctic ice sheet for the period between 2002 and 2005. The loss rate amounts to 152 ± 80 km3 per year, which corresponds to a sea level rise of 0.4 ± 0.2 mm/year (Thomas 2004, Velicogna 2006).

. Fig. 9.12: Structure of Antarctica: The Western ice shield (above) forms the smaller part of Antarctica and is not as resistant to a possible ablation as the Eastern part (http://www.atmosphere.mpg.de/enid/Zukunft_der_Arktis/Eisschmelze_3tz.html)

In some regions, the summer temperatures have increased. In other South polar regions temperature remained constant for the last 50 years or even decreased slightly (Doran 2002). Turner 2005 evaluated 19 stations, and for the past 30 years established a warming for 11 stations, and a cooling for 7 stations. In the case of 4 stations, the trend towards warming reversed in the last years. Particularly the Peninsula strongly warmed at a rate of 0.56 °C/decade. According to a recent study (Turner 2006), the troposphere above Antarc- tica has also warmed up strongly by 0.5 to 0.7 °C/decade in the last 30 years. The reason is 126 supposed to be an observed increase of warm Western winds (westerlies) by a change of the "Southern Annular Mode“ in the past decades. The partly observed temperature decrease in Antarctica, which was not to be expected on the basis of the models, can be attributed to various reasons. On the one hand, the ocean on the Southern hemisphere could have retained an increased amount of heat, on the other hand observations show dynamic changes in the atmosphere. Thompson (2002) proved that over the past years, the "Southern Annular Mode“ (a variability pattern influencing the West- ern winds around Antarctica) had a more positive phase with stronger winds which act as a barrier and thus prevent warm air from the continent to reach Antarctica. As model calculations have shown, this could have been caused by a combination of stratospheric ozone reduction and stratospheric cooling caused by greenhouse gases (Hartmann 2000, Gillett 2003, Shindell 2004). With the expected recovery of the ozone layer, the reverse trend is expected and, with it, a warming of Antarctica. Contrary to the Greenland ice shield, model calculations show a positive mass balance for Antarctica for the next 100 years due to an increasing accumulation (Alley 2005). At present, intensive research is carried out to find out whether the critical Ross glacier flows could start to move during climate warming (Scambos 2004) (Fig. 9.16). If the present movement rate continues, the Western Antarctic ice sheet will have completely vanished within no more than 700 years. In the last years, researchers mainly agreed that the fluctuations between ice ablation and snowfall were more or less balanced. However, according to Monaghan (2006), the annual amount of snowfall in Antarctica has slightly diminished in the last 50 years. In the case of a further warming, the ablation of the edges in West Antarctica and in Greenland is assumed to lead to a considerable sea level rise, particularly due to fears as to an unstable behaviour which is currently not represented correctly by the models. Such a destabilisation of the continental ice was observed around the former Larsen B ice shelf (Alley 2005).

Current State of the Discussion Climate scientists do not agree yet whether the expected increase in snowfall will counter- balance the ablation of the edges. A destabilisation of the Continental ice is not to be ex- cluded.

9.4.3 Arctic Satellite data show that the sea ice cover of the North Pole has strongly shrunk by around 9 % in the last 25 years (in springtime and summer, by around 15 to 20 %). At the same time, the sea ice thickness has been reduced by 15 % and partly by up to 40 % (Fig. 9.13) (Hassol 2004, ACIA report, Lindsay 2005). After all, the sea ice in the Arctic covers a surface of the size of the USA. Yet, the sea ice extension is characterised by decadal fluctuations, as have shown evaluations of the last 50 years. The melting of the summer ice in the Arctic is considered to be another indication for global warming. Scientists found an accelerated ablation, which will extend beyond the fluctuations of the last 100 million years, provided this trend continues. Consequently, the sea level is expected to rise worldwide (Overpeck 2005).

Fig. 9.13: Extension of Arctic sea ice has decreased by 20 % according to satellite evaluations by NASA for the period between 1979 and 2005 (source: NASA) 127 The reasons for these fluctuations are not yet understood in detail (Lemke 2005). One of the reasons surely is the Arctic Oscillation which also shows a decadal fluctuation and which creates an enhanced polar vortex during its positive phase. Further, a connexion to enhanced cloud formation is assumed, which has been observed for the last 40 years. It led to a reduction of the albedo and thus to a reduction of the ice coverage (Ikeda 2003, Chapin III 2005, Overpeck 2005, Wang 2005). Additionally, a haze of aerosol particles from long- distance transports has been observed (Stohl 2006, AWI 2005). As infrared measurements by satellites have shown, the sea surface temperature in the Arc- tic has clearly increased. Furthermore, a rise in air temperature of 0.5 °C per decade could be observed in the last 30 years. Melting sea ice does not raise the sea level, but it enhances the warming trend because the ice sheet reflects more sunlight than the sea surface. This sea/ice/albedo feedback could have a strong impact on the climate of the earth. If this trend continues, the sea ice could have disappeared completely by 2080 (ACIA report 2005). Han- sen (2004a) proves that anthropogenically caused soot coverage additionally enhances the effect of the albedo feedback. Also AWI (2005) stated an aerosol haze above the Arctic (Ritter 2006), which affects the global climate, as model calculations have shown (Dethloff 2006). Arctic temperatures suffer stronger fluctuations than the global mean temperature. The Arctic strongly warmed during the warming period in the first half of the 20th century, it clearly cooled down between 1940 and 1976, and it has strongly warmed again since then. The extent of the temperature rise until 1940 was slightly, but not significantly exceeded until 2004 (Fig. 9.14). According to Bengtsson (2004), the warming between 1935 and 1945 can be attributed to natural causes. Next to natural causes like changes in the Arctic Oscillation (AO), the greenhouse effect could also play a role in the temperature rise over the last three decades (Johannessen 2004). With the Arctic warming of the last three decades, the ice coverage of the Arctic Ocean has decreased as well. Yet, due to Archimedes´ Principle, this did not result in a sea level rise. For the period between 1900 and 2000, Polyakov (2002) found a decrease of the Arctic ice surface with a trend of -0.5 +-0.7 %/decade. The temperature development is similar to the evaluations of the ACIA report. According to Polyakov (2005), the rise in temperature continued, which means that both evaluations of the ACIA report and in Polyakov (2002) lead to comparable results (Fig. 9.14).

Fig. 9.14: Annual anomalies in the land surface air temperature in the Arctic (65° - 90° Northern latitude) for the period between 1900 and 2005, referred to the period of an average between 1961 and 1990 (IPCC 2007))

Model calculations within the framework of the ACIA programme lead us to expect a temperature rise of between 3.5 °C and almost 6 °C by 2100 for the Arctic. Pfeifer (2005) of the Hamburg MPI-M finds similar results with the regional climate model REMO powered by the global model ECHAM 4. Based upon the medium B2 emission scenario, an average temperature increase of 5.5 °C for the period between 2070 and 2079 was calculated for the entire Arctic, compared to the period between 1970 and 1979. Computer simulations were carried out by use of measuring data (aerosols, clouds, radiation) from the measuring campaign ASTAR 2004. They have shown that not only temperatures will be influenced, but also at- 128 mospheric circulation. Particularly the North Atlantic Oscillation - a natural large-scale oscillation pattern - may be changed by it (Dethloff 2005). According to model calculations by the MPI-M for the 4th IPCC Report (AR) with different emissions scenarios, a clear decrease of the sea ice coverage in the Arctic is to be expected until 2100 (see Fig. 9.15).

Fig. 9.15: Model calculations of the retreat of sea ice until 2100 in million km2 with various emission scenarios; time series of the area covered by sea-ice in the northern hemisphere, as an annual average for scenarios A2, A1B and B1 (MPI-M 2006)

These climate-caused changes in the Arctic can have considerable consequences for the earth's climate. Thawing permafrost releases big amounts of fresh water into the arctic basin. This will change the salinity of the North Polar Sea, which may lead to changes of the oceanic circulation pattern. There are discussions about the effects on the Gulf stream - even the interruption of the conveyor belts which transport heat to the North - which are examined in model calculations (see chapter 4.4). Temperatures at the top of the permafrost layer have generally increased since the 1980s in the Arctic (by up to 3° C) (SPM, IPCC 2007). Satellite images since 1981 have proven that the huge forest and tundra regions (Russia, Canada) have turned green and that the vegetation line has shifted in the Northern regions, which after all cover around a quarter of the vegetated land surface of the earth (Jia 2003). Lucht (2002) confirmed this fact in model calculations carried out within the framework of an extensive research project under the direction of the Potsdam Institute for Climate Impact Research (PIK). The tundra regions in Rus- sia and Alaska have turned green in the last decades, but more recent measurements show that the Arctic has become a net source for carbon dioxide and methane. This is due to the increased microbial decomposition of the soil and the release of methane from the thawed permafrost, which again will trigger an enhanced greenhouse effect. A further positive effect next to an extended vegetation period is that the Arctic Ocean will be of interest as a sea route between Asia to Europe (and vice versa). It would shorten the sea route by up to approx. 40 %.

Current State of the Discussion The question as to the causes of these clearly visible changes is intensively discussed by the experts. Are these changes part of a natural cycle since the end of the "Little Ice Age", or are they caused by the increasing concentrations of greenhouse gases? According to the Alfred Wegener Institute in Bremerhaven (AWI), the high complexity of the Arctic climate system impedes reliable prognoses, particularly because natural climate fluctuations play an impor- 129 tant role in the temperature changes of the last decades. Thus, the climate fluctuations of the Arctic (AO) and North Atlantic Oscillation (NAO) have predominantly been in the positive mode since 1970, which means that warm air currents are travelling north. On the other hand, the NAO could be influenced by climate warming, e.g. higher sea surface temperatures, as results from some climate models (Serreze 2005). Through inclusion of these fluctuations into computer models, the prognosis of future climate trends is to be improved considerably (AWI 2005). According to IPCC 2007, Arctic temperatures have high decadal variability, and a warm period was also observed from 1925 to 1945 (SPM, IPCC 2007).

9.4.4 Greenland The ice cap with a thickness of up to 3,000 m and an extension of 1.7 million km2 plays a special role in climate discussions, because its complete ablation would result in a sea level rise by about 7 m. According to satellite measurements, the ice has grown particularly in high altitudes by around 5 cm/year within the last 11 years (Johannessen 2005). This correlates to climate models since warmer and more humid air in this region should lead to an increased snowfall. On the other hand, in the last decades, the ablation of the Greenland ice sheet has accelerated by 0.7 %/year (Fig. 9.17). Measurements at the coast of Southern Greenland showed a decrease in temperatures of approx. -1.29 °C for the period between 1958 and 2001 (Hanna 2003). This cooling is significantly and inversely correlated to the increase of the NAO in the past decades. Yet, since the mid 1990s, a slight temperature increase could be noticed. Chylek 2006 stated that the warming rate between 1920 and 1930 was significantly higher than that between 1995 and 2005.

Fig. 9.16: Schematic representation of glacier movements that flow towards the sea. An acceleration caused by climate warming is feared (http://www.atmosphere.mpg.de/enid/Zukunft_der_Arktis/Eisschmelze_3tz.html)

According to Rigot 2006, recent satellite radar evaluations show an extensive, accelerated glacier retreat between 1996 and 2000. The loss of ice masses has increased by 90 to 220 cubic kilometres per year because of an increase in the flow rate of the glaciers. Zwally 2002 carried out a new calculation of the mass balance for the period between 1992 and 2002 by means of satellite radar evaluations. Zwally 2005 finds a clear decrease of ice masses at the edges of Greenland, but on a whole a slight increase of the total ice masses may be stated. According to Zwally 2006, after 2002, the loss of ice masses at the edges of Greenland accelerated. Hanna 2005 found a statistically insignificant decrease for the years 1998 – 2003.

From satellite measurements, Dowdeswell 2006 calculated a strong increase of the ablation water from the glaciers south of Greenland between 2000 and 2005. After evaluating satellite-supported gravity measurements for the period between 2002 and 2005, Chen 2006 calculated an annual loss of ice masses of 224 ± 41 cubic kilometres. Following evaluations of gravity measurements for the period between 2003 and 2005, Luthcke 2006 also estimates a net loss of ice masses in Greenland of -113 ± 16 Gt/year.

130

Fig. 9.17: Extension of the deglaciation area in Greenland, according to satellite data. It shows the two extreme years 1992 (af ter the eruption of Mt. Pinatubo) and 2005 (a), as well as the chronological trend (b) Source: Steffen and Huff, 2005

The deglaciation area of Greenland ice has again increased, according to Steffen 2005 (http://cires.colorado.edu/science/groups/steffen/greenland/melt2005/). The critical question is whether the increased movement of the glaciers at the edges will remain higher than the compensation due to snowfall in inner Greenland.

Current State of the Discussion Measurements of changes in the Greenland ice and snow masses have not yet shown a clear, long-term trend. But in the case of a continued temperature increase, most of the models show an ablation of the Greenland ice within the next 1000 years. More recent model calculations (Huybrechts 2005) have shown that a global warming of 3 °C would suffice to rapidly melt the Greenland ice. This process could be initiated irrevocably already in 2050, if the greenhouse gases continued to increase. Hansen 2006 apprehends that this process could occur much sooner if glacier masses started to drift due to enhanced ablation at the edges. Climate models are unable to completely reflect this behaviour. According to Over- peck 2006, a comparison with paleoclimate data shows that a sea level rise caused by a warming of the Polar regions could happen much sooner than assumed so far.

9.5 Ocean The oceans cover 71 % of the terrestrial surface and convert solar radiation energy into heat energy mainly in the top layer of the ocean. Additionally, the high specific heat capacity of water leads to the sea having balancing effects particularly for the seasonal temperature fluctuations of the atmosphere.

9.5.1 Warming and Acidification of the Seas In the past 40 years, the oceans have warmed up due to the anthropogenic greenhouse effect (Fig. 9.18 North Atlantic). This is the conclusion drawn by Reichert 2002, Barnett 2005 and Levitus 2005. 131

Fig. 9.18: Anomalies in the mean annual sea surface temperature in the North Atlantic, relative to the average for the years 1961 and 1990 (black bar: average for January – November 2005, grey: smoothed curve), source: Hadley Center, GB, http://www.munich-re.com/publications/302-04772_en.pdf?rdm=46812

The global warming of the sea surface temperature amounted to 0.6 °C, with temperature rises of several degrees in the Arctic region and a cooling of several tenths of degrees off the US-American coast and in the Gulf Stream region. The global average oceanic temperature and the average temperature for the total water column has only risen by 0.04 °C since 1955. The reason for it is that by now, only a superficial layer (the mixed top layer) of some 100 m has warmed, but the average depth of the oceans amounts to 3,800 m (WBGU 2006). Observations have shown that 84 % of the total earth warming (oceans, atmosphere, continents, cryosphere) of the past 40 years has been absorbed by the oceans. The signal is a complex one, and it has a vertical structure, which varies strongly in the oceans. This warming may not be explained by a natural internal climate variability, or by solar and volcanic forcings, but it is well simulated by the results of two anthropogenically forced climate models. Barnett 2005 used a "fingerprint method“ for the temperature trend of the upper 700 m in the different oceanic basins since 1960. It was compared to the results of the model calculations, and it showed a good correlation. Climate scientists like James Hansen, NASA God- dard Institute (Hansen 2005b, c), consider this to be another proof ("smoking gun“) for the anthropogenic climate influence. Lymann 2006 reports a cooling of the sea between 2003 and 2005, as it had already happened between 1980 and 1983. There are still discussions about the extent to which the temperature increase of the sea surface temperature in the tropical and subtropical regions in 1976 (van Loon 2006), which are rooted in a change in the atmospheric patterns, have contributed to this trend.

The additional uptake of CO2 at the sea surface leads to an acidification of the ocean. Ac- cording to Orr (2005), the pH value of the sea surface has declined by 0.1 since the beginning of the industrialisation, and it is calculated to possibly decrease by further 0.3 - 0.4 units by the end of the 21st century. According to IPCC 2007, the average global surface ocean pH will reduce by 0.14 to 0.35 units over the 21st century (SPM, IPCC 2007). Critical ecological consequences for corals and some plankton types, which are at the beginning of the nutrient chain for some fish, are feared (Feely 2004, WBGU 2006). 9.5.2 Sea Level Rise Due to thermal expansion, a temperature increase in the oceans inevitably leads to a sea level rise. Owing to the varying warming of the oceans and rising and sinking movements of many coastlines, the geographic dispersion of rising sea levels varies widely (Fig. 9.19). Ac- cording to measurements (IPCC 2007), the global average sea level rise amounted to around 0.17 m (0.12 to 0.22) in the 20th century. According to Miller (2005), the last years 132 have shown an accelerating increase in the sea level, which now amounts to 2 mm per year. Based on analyses of satellite measurements, Church (2005) states an increase rate of 3.2 mm/year for the period 1993 to 2000, compared to 1.8 mm/year for 1950-2000. For the 1990s, Jevrejeva (2006) states an increase rate of 2.4 mm/year - with big regional differences -, which had, however, already appeared once in the years 1920 to 1945. According to IPCC 2007 the global average sea level rose faster over 1993 to 2003, about 3.1 (2.4 to 3.8) mm per year (1961 to 2003 1.8 ±1.3 to 2.3 mm/yr). Wether the faster rate reflects decadal variability or an increase in the longer-term trend is unclear (SPM, IPCC 2007). By the end of the 21st century, a sea level rise of 0.18 – 0.59 m is expected (SPM, IPCC 2007) (Fig. 9.20 3 scenarios, MPI-M 2006)). Based on his model calculations, Huybrechts (2004) assumes that the sea level rise caused by the loss of Greenland ice masses will be roughly levelled out by enhanced snowfall in Antarctica in the 21st century. In addition to thermal expansion, the ablation of ice also plays a role provided it does not float in sea water. The ablation of alpine glaciers probably contributed to the sea level rise by 2 – 5 cm in the 20th century (IPCC 2001). There are still discussions about the contribution of the Antarctic and Greenland ice. If global warming continues, the long-term ablation of the Greenland ice shield is expected (Gregory 2004), while the East Antarctic ice shield will most certainly grow. The future of the Western Antarctic ice shield is uncertain, because due to its position and the existing probability of a quick ablation of edging areas (for which there are indications), it could suffer big losses in future centuries (Alley 2005). In this area, further measurements, observations and model calculations alike are required in order to receive unambiguous results. Rahmstorf 2006 found a semi-empirical relationship between sea level and temperature rise. As a result sea level rise in 2100 could be with 0.5 - 1.4 m above the 1990 level much higher as in AR4 predicted.

Fig. 9.19: Sea level rise in the last 135 years. The average global increase is currently estimated to amount to 3.1 mm/year (SPM, IPCC 2007).

The sea level rise by 2100 shown in Fig. 9.20 with the model simulations for AR4 to the amount of 20 – 30 cm does not take into account the enhanced ablation of the Greenland ice shield and edge areas of Antarctica (see chapter 9.4), as some scientists fear. However, for the North Atlantic, an additional sea level rise of 20 cm was calculated resulting from changed water circulation. 133

Fig. 9.20: The range of sea level rise according to the IPCC scenarios by 2100, based on the new model calculations of MPI- M for AR4 and observations made in the 20th century MPI-M 2006).

Storage lakes and other artificial water reservoirs also have a clear effect on the sea level. Thus, the well-known major storage lakes contain a water body corresponding to a sea level equivalent of -14 to -28 mm. If all artificial water reservoirs were taken into account, the effect would probably be more than twice as much (Sahagian 2000). This (slightly) counteracts the sea level rise.

9.6 Climate Impacts on Mankind, Nature and Environment Meanwhile, climate impact research has become an individual discipline. Thus, some years ago, the Potsdam Institute for Climate Impact Research (PIK), Germany was established, which by now, among others, has published several regional studies (Germany, Branden- burg, Baden-Württemberg, Bavaria) about this topic. The impacts of climate change (temperature increase, changes in precipitation, sea level rise etc.) may influence man and nature in different ways: - Health (deaths due to extreme heat or cold, infections, communicable or other diseases) - Agriculture (crop yield, irrigation) - Water resources (water stocks, water quality, competition for water) - Coastlines (erosion of beaches, flooding of islands, coastal protection) - Flora and fauna (loss of species, changes in the habitat, glacier shrinkage) - Infrastructure (destructions due to storms and floods) - Tourism (less winter sports, more summer vacations e.g. at the North Sea and Baltic Sea) According to Schönwiese (2006), the following positive (+) and negative (-) impacts of climate change should be expected (examples):

134

+ Reduced heating requirements in the temperate (winter) and subpolar climate zones + Reduced stress due to cold temperatures in the temperate (winter) and subpolar climate zones + Extended vegetation period and improved possibilities for agricultural use in the temperate climate zone (favourable soil and water conditions assumed) - "Misreactions" of ecosystems (e.g. leafing in warm winters) - More favourable conditions for the expansion of plant pests and pathogens - Flooding of island countries and delta regions (due to sea level rise) - Summerly heat waves in the temperate, subtropical and tropical climate zone - Regional problems of water supply (e.g. in the Mediterranean) - More frequent floods (e.g. in the temperate climate zone, in winter) in some regions - More storm damage (?)

In model studies about the vulnerability of the European ecosystem in the case of a global climate change, Schröter (2005) reports of positive as well as negative impacts. In 2005, the PIK research project "Climate Change in Germany - Vulnerability and Adaptation Strategies of Climate-Sensitive Sectors" offered concrete regional estimations (http://www.umweltbundesamt.deKlimaschutz/).

9.6.1 Damage – Statistics, Costs The extent of losses caused by natural events is generally predominantly determined by the number of affected people living in exposed areas: with an increasing population, the values exposed to hazards emanating from nature, increase nearly proportionally. Particularly river meadows and coastal regions are intensely used as cheap, attractive building land for residential, industrial and trading areas. Moreover, residential houses are much more valuable today than they were in earlier times. This increases dramatically the amount of loss in the case of floods or storm tides (Munich Re Group 2005). In Germany, the new Flood Control Act is designed to counteract this development by the identification of "retention areas". According to Munich Re Group (2005), the following factors are responsible for the increase of natural disasters:

Population growth Higher standard of living Concentration of people and material goods in megacities Settlement in regions with a high threat of natural hazards Increased vulnerability of modern technologies Increased insurance density Changes in the environment - climate change

Statistics of Natural Disasters Statistics about natural disasters caused by weather, earthquakes and volcanic eruptions (Fig. 9.21), and their damage to national economies, which are particularly drawn up by insurance companies such as the Munich Re Group, have to be considered with caution. The increase in the amount of loss is not inevitably connected to an increase in storms, floods or precipitation. Often man himself has contributed to an increase in the amount of loss by settling in critical areas like coastal zones or at river banks. 135

Fig. 9.21: Global trend of major natural catastrophe, divided up by type of event between 1950 and 2005 (Munich Re Group 2006)

At the workshop “Climate Change and Disaster Losses — Understanding and Attributing Trends and Projections” in Hohenkammer in May 2006, the participating climate scientists (among others, von Storch and R. Pielke jr.) and representatives of the insurance industry published a statement with recommendations for action (http://www.munich- re.com/Templates/Special/PrintPage.aspx?lang=de¤t_page=/pages/03/georisks/geo_ climate/workshop_climate_change_02_de.aspx?print=yes). The document states as follows: 1. Climate change is real, and has a significant human component related to greenhouse gases. 2. Direct economic losses of global disasters have increased in recent decades with particularly large increases since the 1980s. 3. The increases in disaster losses primarily result from weather related events, in particular storms and floods. 4. Climate change and variability are factors which influence trends in disasters. 5. Although there are peer reviewed papers indicating trends in storms and floods there is still scientific debate over the attribution to anthropogenic climate change or natural climate variability. There is also concern over geophysical data quality. 6. IPCC (2001) did not achieve detection and attribution of trends in extreme events at the global level. 7. High quality long-term disaster loss records exist, some of which are suitable for research purposes, such as to identify the effects of climate and/or climate change on the loss records. 8. Analyses of long-term records of disaster losses indicate that societal change and economic development are the principal factors responsible for the documented increasing losses to date. 9. The vulnerability of communities to natural disasters is determined by their economic development and other social characteristics. 10. There is evidence that changing patterns of extreme events are drivers for recent increases in global losses. 11. Because of issues related to data quality, the stochastic nature of extreme event impacts, length of time series, and various societal factors present in the disaster loss record, it is still not possible to determine the portion of the increase in damages that might be attributed to climate change due to GHG emissions. 12. For future decades the IPCC (2001) expects increases in the occurrence and/or intensity of some extreme events as a result of anthropogenic climate change. Such increases will further increase losses in the absence of disaster reduction measures. 136 13. In the near future the quantitative link (attribution) of trends in storm and flood losses to climate changes related to GHG emissions is unlikely to be answered unequivo- cally.

Fig. 9.22: Development of major weather disasters between 1950 and 2005, and losses of national economies (Munich Re Group 2006). The increase in losses does not allow a statement about the increase in natural events Figure 9.23 shows for Germany that storms and floods have the biggest share in natural hazards. The figure shows an increase in losses due to natural events like storms. As explained by Munich Re Group upon request, however, this is not correlated to an increase in the frequency of storms. 137

Fig. 9.23: Trend of natural disasters in Germany 1970 – 2005 (earth quakes, storm, floods, temperature extremes); it should be taken into account that only the number of events is shown (Munich Re Group 2006)

As explained in the chapters 9.1 to 9.5, a regional increase in storms, floods, storm tides, inundations and heavy precipitation, heat waves and droughts is to be expected in the case of a continued climate warming (Bartels 2006, von Storch 2005, PIK Study 2005). Economic impact There is a great deal of uncertainty associated with costing climate change impacts. Working Group 3 ‘mitigation’ of the IPCC will bring in 2007 new results in this field. As an example two studies are summarised: According to Kemfert (2004), it is possible to estimate the economic impacts of climate change on the basis of the global simulation model WIAGEM, which cou- ples a detailed economy and trade model with a climate model. In addition to direct economic impacts on energy generation, agriculture and industry, also impacts of climate change on ecology (e.g. the increase of forest fires, loss of biodiversity) were considered, as well as aspects of health and economy (e.g. diseases, changes in mortality). A temperature increase of 1 °C could cause global losses of up to 214 trillion US dollars for a period of 50 years. In the year 2050 only, this would equal losses to the amount of globally up to 2 trillion US dollars. The amount of loss depends on the assumptions made for future developments, which entail major uncertainties. Thus, from an optimistic point of view, such losses could result to be far less, but from a pessimistic point of view, they could also be twice as high (Kemfert 2004). In his study (Stern 2006) to the British Government, Stern, former President of the World Bank, states that there still is some time to avoid the worst impacts of climate change if actions are taken at once. The total amount of loss caused by climate change could amount to annually 5 % (in the worst case, to annually 20 %) of the gross world product - without actions taken. Quick action for the reduction of greenhouse gases would require around 1 % of the gross world product in order to avoid the worst impacts. Adaptation Strategies The sensitivity, adaptive capacity, and vulnerability of natural and human systems to climate change, and the potential consequences of climate change, are assessed in the report of 138 Working Group II of the IPCC. Adaptation to climate change has become an important policy priority in the international negotiations on climate change in recent years. Many international reports (UN, WHO, EU) are discussing this issue. Especially the least developed countries (LDP) need help because they are amongst the most vulnerable to the adverse impacts on climate change. According to PIK (Zebisch 2005), it is necessary to create a consciousness for risks and possibilities on the way towards a Germany that has adapted to climate change. According to the principle of prevention, concrete decisions of adaptation measures - e.g. dike heightening due to increasing flood hazards - should be taken soon. In Germany, it would be possible to keep climate impacts (vulnerability) to a low level for most of the regions if all available measures for adaptation were carried out (Zebisch 2005). To this end, the KomPass Compe- tence Centre for Climate Impacts and Adaptation was founded at the Federal Environment Agency on 17 Oct. 2006 (Umweltbundesamt, UBA).

9.6.2 Health Climate change has the potential to significantly influence the health of people around the world. The WHO (Patz 2005) estimates that the anthropogenically caused warming and precipitation trend has caused the death of about 150,000 people per year over the past 30 years. However, it was conceded, that this statement may entail a high degree of uncertainty due to missing reliable long-time data, the major influence of socio-economic factors and changes in the immune behaviour and drug resistance. It is an indisputable fact that the developing countries are particularly endangered. In addition to fatalities attributable to heat (e.g. the extreme summer of 2003 with 22,000 to 45,000 fatalities in Europe) and deaths due to nutritional deficiencies and inundations, also infectious deaths are examined. Thereby, Malaria and the Dengue fever play a prominent role. Diseases like diarrhoea and cholera, which are influenced by water, are of special significance in countries like Bangladesh or Peru. According to WHO, fatalities are expected to double by 2030 due to anthropogenic climate warming. Particularly those countries around the Pacific and Indian Ocean are endangered, which are characterised by strongly varying rainfall - caused by El Niño/Southern Oscillation -, as well as Africa above the Sahara. Also large cities with their urban heat island effect are able to enhance extreme climate events. Changing threats of the various vector-borne diseases could be reduced by the development and implementation of more effective disease prevention strategies and public health infrastructure and practice.

Malaria Malaria transmitted by the anopheles mosquito ranks among the most important vector- borne diseases worldwide. At present, around 2.4 billion people, or 40 % of the world population, live in 101 states and territories with malaria hazard. 400-500 million people are newly infected per year, and more than one million people, mostly children under 5, die annually of malaria infections. More than 80 % of the Malaria cases occur in Africa south of the Sahara. IPCC statements about a strong increase in Malaria infections attributable to climate change are characterised as "uncertain". According to Epstein (2000), Fig. 9.24 represents the predicted change of Malaria by 2020 compared to the average risk between 1961 and 1990. Some regions in Northern Europe and Russia are classified as being newly endangered regions. In contrast to the IPCC Report 2001, and based on model calculations, Rogers (2000), Dye (2000) state that also in the case of extreme climate scenarios the global extension of Ma- laria will change only slightly. According to Hay (2002), the resistance to drugs and missing repelling measures are a greater danger with respect to a spreading of Malaria, than climate changes. Reiter (2004) warns of unjustified generalisations concerning a possible spread of Malaria infections. None of the model calculations considers adaptation measures in health care, the development of new therapies or changes in the human behaviour, which could lead to a considerable drop of malaria hazards. After all, even in temperate countries like England, Germany (http://www.umweltdaten.de/publikationen/fpdf-k/2291.pdf), Sweden or 139 even Finland, there were many Malaria cases in the 18th and 19th century which could be eradicated by applying respective measures. A further problem is the regional assessment of health impact, because the climate change projection for the AR4 are still not appropriate for analysing disease patterns at smaller scales (<250 km) (Patz 2005).

Fig. 9.24: Predicted changes of Malaria. Transmission by 2020, compared to the average risk between 1961 and 1990 (source: Kasang, HBS 2005, according to Epstein 2000)

Dengue Fever Dengue is caused by various types of virus transmitted by certain mosquitoes, which prefer particularly human blood. Dengue is primarily an urban tropical disease and has developed into a major health problem there. The transmission to man occurs all-year, with a peak in months with heavy precipitation and high humidity. Annually, 50 to 100 million people are infected. Main reasons for the current quick spread of the disease are the general population increase, quick urbanisation, missing effective measures for fighting the mosquitoes, and the cross-border spread of new types of Dengue viruses. Similar to Malaria, also the outbreak of Dengue epidemics depends on climate conditions, although due to the population density, this effect is not so important for cities. In the Tropics, Dengue epidemics often occur during months with heavy precipitation and high humidity, and there is a correlation to the ENSO phenomenon (Hopp 2001, 2003). According to model calculations, which, however, like the Malaria models do not consider social factors and those of medical prevention and increase mosquito control efforts, an assumed global average temperature rise of 2 °C by 2100 will lead to a net increase in the spread of Dengue.

Ticks In Central and Northern Europe and in the USA, particularly the climate-depending vector- borne diseases meningoencephalitis and Lyme borreliosis, both transmitted by ticks, play an important role. Encephalitis transmitted by ticks is a viral disease, which may lead to infections of meniges, brain and spinal marrow. There is no effective therapy against it. Lyme borreliosis is caused by bacteria and can be treated with antibiotics. In the 1990s, Lyme borreliosis spread widely in the USA (Brownstein 2005). Encephalitis by ticks is still a rare but increasingly serious problem because it may be fatal. In endemic areas, 1 to 4 % of the ticks are infected. The mild winters of the last years have strongly favoured the chances of sur- vival of ticks and their host animals (smaller forest rodents and red deer). Therefore, the transmission intensity could start on a significantly higher level in the respectively following years, because there was no need to first build up new populations. Changes of human behaviour with respect to leisure-time activities are also of importance. 140 Owing to the fact that springtime starts earlier, winter starts later and winter temperatures are milder, also in Scandinavia tick-transmitted encephalitis has also spread. For the first time, empirical studies conducted in Sweden created a reliable context between climate data and the spread of encephalitis transmitted by ticks. In particular the increasingly milder winter temperatures of the last decades, which climate models had calculated to be a typical effect of the anthropogenic greenhouse effect, have obviously led to a higher infection rate (http://www.euro.who.int/document/E89522.pdf).

9.6.3 Benefits The discussion about possible consequences of the climate warming often tackles negative impacts only. Thereby, it is overlooked that some regions may even enjoy positive effects. The problem is to correctly assess a possible turn from positive to negative consequences. A moderate temperature increase should have mostly positive consequences.

Among them is e.g. CO2 fertilisation. A higher CO2 content in the atmosphere accelerates and enhances the growth of many plants which results in improved crop yields. The increase in wood in the Central European forests in the last years, which has been observed despite the forest damages, is also attributable to the effect of a higher CO2 content in the atmosphere. However, this does not work all the same for all the plants, and it works only as long as there is no lack in nutritional agents and water for plants. So-called C4 plants (tropical grasses, sweetcorn and sugar cane) do not show any or only little enhanced growth due to an increased carbon dioxide concentration, but their transpiration is reduced. In contrast thereto, C3 plants (practically all trees, most of the agricultural products including wheat and rice) enhance their growth. An increased CO2 concentration reduces the water evaporation (transpiration) of plants because leaf openings (stomata) are partly closed. Experiments have shown that in the case of a doubled CO2 concentration, the growth of a young pine wood may amount to 25 %. According to Norby (2005), young forests showed a net primary production increase, but according to Körner (2005), this was practically not the case for older trees over 35 m. The corresponding increase amounted to 33 % for cereals (Fig. 9.25) (IPCC 2001). However, different values are reported for the limit, beyond which there is no or only minor increase in plant growth. Not all the experimental studies confirm the often stated value of 800 to 1,000 ppm. Higher temperatures also promote the growth of many plants, and accordingly, the vegetation period is prolonged. Initially, certain regions in Europe, Russia, USA, Canada and parts of Asia will profit from higher crop yields (Fig. 9.25). Obviously, there is an upper and lower temperature limit for plant growth, and the maximum net photosynthesis or highest yield occur within a certain temperature range. For most of the plants in the mid-latitudes, this temperature range lies between 18 and 25 °C, e.g. for winter wheat between 17 and 23 °C, for sweetcorn and rice between 25 and 30 °C, for potatoes and soybeans between 15 and 20 °C (IPCC 2001). Consequently, there will be losses in the crop yield, if the temperature rise is too strong and/or water shortages occur. The 2003 heat wave in Europe was exemplary for it. Measurements and calculations (Ciais 2005) showed a decrease in the primary vegetation production of around 30 % in this period. The critical limit for a global temperature rise is often reported to be approx. 2 °C (IPCC 2001). If the temperature increases beyond 3-4 °C, it is generally assumed that impacts will be negative (OECD 2005). Most certainly, Africa will profit least of a carbon dioxide increase because already now, temperatures lie within a critical range, and water shortages in certain areas will even aggravate. Higher temperatures reduce the number of frost days in winter, and thus they also reduce heating requirements, but in summer, energy requirements will rise due to then necessary increased cooling. The fact that the Arctic Ocean may be ice-free will allow navigation to take this route and thus considerably shorten the sea route e.g. to Asia by approx. 40 %. Additionally, it could be possible to exploit natural resources like crude oil, natural gas and ore (copper, nickel etc.). On the other hand, regional nature could suffer significant ecological impacts. 141

Fig. 9.25: Regionally varying impacts on crop yields of cereals at different carbon dioxide concentrations according to model calculations (Parry 2005, http://www.stabilisation2005.com/day1/Parry.pdf)

Examples could be continued at own discretion. However, the intention was only to show that a unilateral consideration of possible climate impacts is not justified. The 4th IPCC Report WG II will make further concrete statements about this topic. On the long term the greater majority of impacts are likely to be negative.

9.7 "Hazardous Climate Change" At the Rio de Janeiro Earth Summit in 1992, it was decided within the United Nations Framework Convention on Climate Change to strive for a stabilisation of greenhouse gas concentrations at a level, which prevents hazardous anthropogenic disturbances of the climate system. This limit value, beyond which the impacts of climate change are said to be hazardous and unsustainable for mankind, is still being discussed. The Exeter Symposium in 2005 – Avoiding Dangerous Climate Change – (Schellnhuber 2005), dealt with this topic extensively. In conclusion, it was established that major efforts will be necessary to meet the 2 degree limit which is often considered to be an acceptable value for a global average temperature increase. But, according to the conference report, already in a world, which is two degrees warmer, mankind will have to adapt to crop yield losses, the extension of deserts and water shortages for up to three billion people. In 2005, the European Council and other panels like WBGU (WBGU 2005) opted for the target to limit the warming to under 2 °C. To this end, the carbon dioxide concentration should clearly remain below 550 ppm, around approx. 450 ppm. Meinshausen 2004 studied the different emission scenarios and found that the 2 degree limit will most probably be exceeded in the case of a CO2 concentration of 550 ppm. Hansen (2003, 2004 b, c) already considers 1°C to be the limit, as he fears that the sea level rise will occur much sooner, if parts of the Greenland and Western Antarctic ice shield melt much quicker than previously assumed consequent upon instabilities in these regions. Another hazard is deemed to be the reversing or decelerating Thermohaline Circulation (THC). This could be triggered by the influx of fresh water coming from melting ice in the Polar regions or increased river waters from Siberia proceeding from thawing permafrost. Compared to the IPCC scenarios, the increase in greenhouse gas emissions - particularly for CFCs and methane - has dropped in the last years (see chapter 5.1) in such a way that the 142 present increase rates lie at the lower limit. On the other hand, the carbon dioxide concentration continues to rise, and the increase rate from the combustion of fossil fuels amounts to 2 % per year. Many climate researchers believe that it will only be possible to meet the 2 degree limit if the carbon dioxide emissions are reduced very rapidly on a global scale (alternative scenario) (Fig. 9.26) (Rahmstorf 2006, WBGU 2003, Exeter 2005, Hansen 2005a, b, c, d).

(b)

Fig. 9.26: (b) Annual strongly fluctuating increase of carbon dioxide in ppm/year, (c) total increase of the radiative forcing of greenhouse gases in W/m2, right graph: increase rate of the radiative forcing of the greenhouse gases since 1950, as established by the IPCC scenarios B1, A1B, A1, F1, and by the alternative scenarios 1 ° C (red line) and 2 ° (grey line) (Hansen 2005)

The climate researchers (Meehl 2005, Rahmstorf 2006) assume that even if the CO2 increase was immediately stopped, the average temperature of the earth would continue to rise by approx. 0.5° C within the next 50 years, until a state of equilibrium was reached (SPM, IPCC 2007). 143

10 Emissions from Energy Conversion and Energy Transport Energy conversion and, to a limited extent, energy transport inevitably generate climate- relevant gases. With 82.8 % (2004), the energy sector (power industry, industry and traffic) is the biggest source for greenhouse gas emissions in the industrialised countries (Annex I Countries) (UNFCCC 2006). Within the EU-15, the energy sector contributes to the emission of greenhouse gases with 81.2 % (2003). In this sector, the emissions have increased by 2.5 % to 3.4 billion t CO2 equivalents between 1990 and 2003. With 78.6 %, CO2 has the principle share in it (FCCC 2005). In 2004, public electricity and heat supply contributed to the greenhouse gas emissions with 24 % in CO2eq and 28% on carbon dioxide emissions within the EU-15. The German power industry causes around one third of the German carbon dioxide emissions, and therefore, it is particularly challenged in the discussion about reduction possibilities. Figure 10.1 shows the development of the greenhouse gas emissions within the EU-25. According to this graph, EU-15 was able to reduce its emissions by 1.2 % so far, and EU-25 by 5.6 %. The strong reduction of over 24 % in the new EU countries is rooted in the economic changes and the modernised industrial plants.

1990 1995 2000 2002 2005 Absolute Change Emission Change in 2005 Target by in 2005/ Base- 2008/12 1990 line according Year to Kyoto 1990 Protocol in million t carbon dioxide equivalents in %

Belgium 145.8 152.3 147.4 145.1 150.2 3.3 + 2.3 - 7.5 Denmark 69.0 76.3 68.2 68.9 63.7 -5.3 -7.7 - 21.0 Germany 1227 1095 1023 1019 994 - 236.8 - 19.2 - 21.0 Finland 71.2 71.5 70.0 77.5 69.8 -1.4 - 1.9 0.0 France 570.8 565.0 564.4 558.8 562.8 - 8.1 - 1.4 0.0 Greece 108.8 113.2 131.9 133.0 136.5 27.7 + 25.4 + 25.0 Great Britain 764.5 704.0 663.5 651.7 657.6 - 106.9 - 14.0 - 12.5 Ireland 55.6 58.9 68.7 69.0 69.9 14.3 + 25.8 + 13.0 Italy 519.8 532.8 554.9 561.8 583.9 64.1 + 12.3 - 6.5 Luxembourg 12.7 9.9 9.6 10.8 14.2 1.4 + 11.4 -28.0 Netherlands 213.0 225.1 214.5 214.9 219.8 6.9 + 3.2 - 6.0 Austria 79.0 80.2 81.3 86.9 94.1 15.1 + 19.2 -13.0 Portugal 60.1 71.5 82.3 88.3 83.9 23.7 + 39.5 + 27.0 Sweden 72.5 74.0 68.6 70.2 69.0 - 3.6 - 4.9 + 4.0 Spain 287.2 317.9 384.2 402.1 441.6 154.4 + 53.8 + 15.0

EU-15 4261 4148 4133 4158 4210 - 50.9 - 1.2 - 8.1 New Member 979.0 804.2 745.7 727.1 757.5 - 242.1 - 24.2 - 6.8 States EU-25 5261 4952 4879 4885 4968 - 293 - 5.6 - 7.8

Fig. 10.1: Development of greenhouse gas emissions in the EU-25 between 1990 and 2005 in million t CO2 eq, and proportional changes and Kyoto targets according to the EU burden sharing (source: DIW Wochenbericht Nr. 35/2006 from UNFCC, national emission inventories)

The new UNFCCC Report, published on 30 Oct. 2006 (UNFCCC 2006), shows that in 2004, the total emissions of the industrialised countries, which are member states of the Kyoto protocol, amounted to 15.3 % below the 1990 value. This was mainly caused by the strong de- 144 crease in Central and Eastern Europe of approx. 36 %. However, for the period between 2000 and 2004, there was a slight increase of approx. 2.9 %. Figure 10.2 shows the emission decrease of the six greenhouse gases pursuant to the Kyoto Protocol in Germany for the years 1990 – 2003. With 994 million t CO2 equivalents, the Kyoto target of 969 million t was nearly met in 2005 (NIR 2006, DIW 2006).

Fig. 10.2: Decrease of the greenhouse gas emissions in Germany in million t CO2 equivalents for 1990 to 2003 (from: NIR 2005); in 2005 they still amounted to 994 million t (NIR 2006, DIW 2006)

10.1 Emissions of Water Vapour, Waste Heat As is to be shown in the following, the anthropogenic contribution to water vapour emissions and waste heat is negligible on a global level. The power industry basically contributes to water vapour emissions. According to Zittel (1994), the generation of 1 kWh heat energy emits around 60 g of water during the combustion of coal, 115 g during the combustion of oil, and 162 g during the combustion of gas. Wa- ter vapour is also emitted during the operation of cooling towers. Zittel calculates an average value of 1.5 kg per kWh (el). Zittel 1994 estimated the absolute amounts of water vapour emissions in Germany to be as follows: With an annual average amount of precipitation of around 780 mm, and a surface of approx. 360,000 km2, the volume of precipitation amounts to approx. 280 billion t. The natural water vapour emissions per km2 and year amount to around 0.35 x 106 t. In relation to the total surface, around 125,000 x 106 t of water vapour are emitted per year. This figure was calculated under the constraint that around 50 % of the total amount of precipitation evaporates, and the remaining 50 % flow via ground and superficial water into the sea. If the annual evaporating water vapour emissions emanating from the surface of Germany are compared to the water vapour emissions of the total German industry, including power plants and cooling towers, the industrial share amounts to less than 1 %. Considering the enormous amount of natural evaporation particularly by to the oceans, the anthropogenic fraction is negligible on a global scale (0.005 %). The biggest part of anthropogenic emissions of water vapour is caused by irrigation (Boucher 2004). Concerning the anthropogenically generated waste heat, Graßl (2004) states the following with respect to the global energy budget: "As far as the waste heat is concerned, which is the 145 most obvious disturbance of the energy budged by industrialised mankind; it is easy to carry out an assessment. The energy flux density of 0.025 W/m² resulting from an average 2 kW power which is approximately used per capita at present, might be neglected on a global scale compared to the solar energy on the terrestrial surface of around 170 W/m2“. (Author's remark: The above stated value of 2 kW power is derived from the average global energy consumption of 17,500 kWh per capita and year). In urban areas, waste heat produced by human activities plays an important role for local climate change (Crutzen 2004).

10.2 Carbon Dioxide Emissions The carbon dioxide emissions have almost constantly increased since the beginning of the industrialisation, which is primarily due to the combustion of fossil fuels. Figure 10.3 shows the increase in carbon dioxide emissions due to the combustion of fossil fuels (coal, oil, gas) and the contribution of gas flares and cement production since 1850. Thereby, a total of about 300 billion t of carbon has been released into the atmosphere since 1750, half of it since the mid 1970s. On a global scale, the combustion of solid and liquid fuels accounts for 76.8 % of the emissions, and the combustion of gas for 19.3 % (2002). Cement production emits around 3.5 %, and gas flares less than 1 % (Fig. 10.3) (Marland 2005).

Fig. 10.3: Development of the global carbon dioxide emissions between 1751 and 2002 proceeding from solid, liquid and gaseous fuels, as well as from flaring and cement production (http://cdiac.esd.ornl.gov/trends/emis/glo.htm)

In the period between 1960 and 2005, energy-attributed carbon dioxide emissions have more than tripled and currently amount to 7.5 billion tons (approx. 27.3 billion t CO2, DIW (2006)) per year. For the period 1990 – 2005, the global CO2 emissions attributed to energy increased by 5.8 billion t (+26.8 %) to 27.3 billion t. In 2004, emissions increased by around 4.5 % and in 2005 by around 2.5 %. Nearly 65 % of the increase in emissions since 1990 have been caused by China (+ 2.5 billion t), USA (+ 982 million t) and India (+ 525 million t) (DIW 2006).

Compared to 1990, with 14.8 billion t, the carbon dioxide emissions of the industrialised countries (without USA and Australia, because they are not members of the Kyoto Protocol) (Annex I Countries) have slightly increased by around 3 % in 2005. In contrast thereto, the emissions of the developing and threshold countries (Non Annex I Countries) have clearly increased by 73.8 %. With 109 %, the strongest increase was caused by the Asian states such as Thailand, Malaysia and South Korea. With + 108 % and an emission value of 4.77 billion t, China also made a big step forward. Meanwhile, with a carbon dioxide emission of 12.5 bil- 146 lion t, the Non Annex I States have a share of 46 % in the global energy-attributable carbon dioxide emissions.

In 2005, the USA continued to be the leading carbon dioxide emittent (21.9 %), followed by China (17.4 %), the EU-25 (15.0 %), Russia (5.7 %), Japan (4.7 %) and India (4.1 %) (DIW 2006) (Fig.10.4). The German share in the global carbon dioxide emissions amounts to 3.2 %. Today, those 35 states with quantified reduction obligations, which have ratified the Kyoto Protocol, are responsible for less than 30 % of the global CO2 emissions. If the trend continues, China and India will have surpassed the USA within a few years (Fig. 10.5, 10.6) (BMU Statusbericht 2006, DIW 2006).

Fig. 10.4: Share in fossil CO2 emissions according to countries for 2005 (DIW 2006)

Within the EU, carbon dioxide is responsible for 82 % of the greenhouse gas emissions, followed by methane, dinitrogen oxide and the F (Fluor)-containing greenhouse gases (Annual GHG Inventory Report 2005). According to calculations with energy scenarios of WEO/IEA, the carbon dioxide emissions will increase by 70 % and amount to 38 billion t by 2030, compared to 2002 (Fig. 10.5). The developing countries will have the biggest share with an increase of 2/3 (World Energy Out- look 2004). In 2006, the US American Energy Agency assumed an increase of 75 % to 44.5 billion t CO2 by 2030. According to calculations of the EU Commission, this value could be reduced by 21 % with a "CO2 reducing scenario“. (http://www.euractiv.com/de/energie/energie-prognosen/article-103637)

147

Fig. 10.5: Development of the worldwide energy-attributable CO2 emissions for 1990 – 2030, according to regions (from: VGB 2005, UNFCC 2004)

Figures 10.6 and 10.7 clearly show that the main increase rates for carbon dioxide emissions today are in Asia. The USA and Australia also, which have not joined the Kyoto Protocol, still have increase rates of 20 % and 26 %, respectively, for the period between 1990 and 2005. The EU-15 emissions have nearly stabilised, in particular due to the heavy reductions in Germany and Great Britain. For the same period, a clear reduction is shown for the new EU countries and Russia with 25 % and 30 %, respectively.

Fig. 10.6: Trend of the carbon dioxide emissions of leading Annex B and Non-Annex B countries 1990 – 2002; the values for 1990 correspond to 100 % (RF = Russian Federation) (Zittel 2004, http://www.germanwatch.org/rio/apbpst04.pdf)

148 1990 1995 2000 2005 1990 – 2005 CO2 emissions in million t Changes in % USA 5005.3 5325.3 5864.5 5987.1 19.6 Japan 1138.8 1219.5 1251.1 1293.5 13.6 China 2289.0 3012.4 2973.2 4770.2 108.4 India 597.7 796.2 997.1 1122.8 87.8 Latin America 601.6 719.0 856.0 919.6 52.9 Annex-II- 10,347.7 10738.8 11507.9 11884.7 14.9 Countries (1) World (2) 21573.9 22485.2 24015.4 27345.6 26.8 World without PP 19284.9 19472.8 21042.2 22575.4 17.1 China Annex-I- 14395.4 13815.5 14354.0 14872.4 3.3 Countries (3) Non-Annex-I- 7178.4 8669.7 9661.4 12473.3 73.8 Countries (4) Annex-I- 3908.1 2904.9 2622.3 2729.3 -30.2 Economies in Transition (EIT) (5)

(1) Annex II-Countries: "Western industrialised countries" without USA and Australia (2) World: including open ocean storage and international air traffic (3) Annex I-Countries: OECD Countries and Transforming countries without South Korea and Mexico, as well as without USA and Australia (Kyoto Protocol not signed) (4) Non-Annex I-Countries: mainly developing and threshold countries (5) Annex I-Economies in Transition (EIT): transforming countries (Russia, Ukraine, Byelorussia and former Eastern Bloc countries)

Fig. 10.7: Energy-attributable CO2 emissions of some selected countries and regions between 1990 and 2005, and proportional share in changes, source: DIW Wochenbericht (weekly report) No. 35/2006

The German share of the global energy-related CO2 emissions has decreased from 4.5 % to approx. 3.2 % between 1990 and 2005. In the same period, the emission share of the USA increased by around 20 %. By 2005, Germany was able to reduce its greenhouse gas emissions by 19.2 % compared to the baseline year of 1990. Thus, the Kyoto target has come into a close reach (NIR 2006). A comparison of the trends of the individual EU-15 member states shows that in the 1990s, Germany made by far the biggest absolute contribution to the reduction of climate gases.

According to the provisional continuation of the National Inventory Report for 2005 (NIR) for Germany between 1990 and 2004, the sectorial development is depicted as follows (Fig. 10.8): Between 1990 and 2004, the carbon dioxide emissions in Germany were reduced by around 15 % from 1,021 million t to 868 million t. The power industry reduced its emissions by approx. 14 % from 409 million t to 355 million t (Fig. 10.8, slightly corrected figures compared to Fig. 10.9). According to statements by DIW (2006), the emissions were reduced from 1,030 million t to 865 million t between 1990 and 2005. (The 1990 value was corrected to be 1,030 in NIR 2006). Flue gas desulphurisation with limestone as SO2 absorbent, as it is used in the power plants, causes CO2 emissions of around 1.6 million t per year (NIR 2006). 149

CO2 emis- 1990 1995 2000 2001 2002 2003 2004 sions

Power in- 408.7 351.7 340.1 345.7 352.8 358.8 355.1 dustry

Industry 233.8 186.5 172.6 167.4 165.2 167.8 171.4

Traffic 162.4 176.6 182.3 178.3 176.2 170.2 171.1

Domestic 129.4 129.2 116.8 131.2 120.1 122.4 115.6 Households

Trading 86.7 65.2 56.1 59.1 56.2 57.6 55.0

Total 1021.1 909.1 868.0 881.8 870.4 876.9 868.3 emissions*)

*) Differences in the sum are due to the respective rounded values

Fig. 10.8: Sectorial trend of the total energy-attributable CO2 emissions in Germany for 1990 – 2004 in million t (source: BMU Statusbericht 2006)

Fig. 10.9: Trend of the carbon dioxide emissions in Germany according to consumer groups (power industry, processing in industry, traffic, domestic households and small consumers, industrial processes) for 1990 – 2003 (UBA 2005)

The National Inventory Report 2005 (NIR) concludes the following:

- In the energy sector, CO2 emissions decreased by 56 million t between 1990 and 2003. Since 1999, CO2 emissions increased again around 21 million t due to a take-over of the operation of industrial power plants and an increased use in lignite and natural gas. 150

- In the industrial sector, emissions continue to decrease. Between 1990 and 2003, CO2 emissions were reduced by around 65 million t (approx. 33 %). The reduction rate has clearly decreased compared to the first years.

- The trend line of CO2 emissions by domestic households shows that emissions have decreased on average. - By the end of the 1990s, emissions by traffic have drastically increased. Due to the self- obligation of the automotive industry and the further development of emission stan- dards, the specific emissions clearly decreased. The increased - particularly commercial - traffic volume partly neutralised these improvements. Until 1999, emissions caused by traffic increased by 15.1 %. Thereafter, they sank by 15.4 million t due to reduced fuel sales, but by 2003, they still were 8.4 million t higher than in 1990.

10.3 Methane Emissions Figure 10.10 shows the trend of global anthropogenic methane emissions between 1860 and 1994. Particularly increased cattle raising and rice cultivation, as well as exploitation of coal, landfills, gas supply and biomass combustion lead to an increase in methane emissions in the past (see chapter 5.1.3)

Fig. 10.10: Increase of the methane emissions in million t (Tg) since 1860 (source: www.cdiac.esd.ornl.gov/)

Methane is a main component of natural gas, landfill gas, biogas and sewage gas. Methane is also emitted by oil sources (gas flaring) and during the transport of natural gas (gas supply) (Fig. 10.10). According to IIASA (2006), particularly in Asia and Africa, the anthropogenic methane emission has increased by 16 % from 290 million t to 335 million t between 1990 and 2000. The EU reduced its methane emissions by approx. 24 % from 24 to 16 million t from 1990 to 2003 (Key GHG Data 2005). Between 1990 and 2004, methane emissions were reduced by 4.8 million t to 2.5 million t in Germany (2006). With nearly 50 %, the main share is attributable to agriculture. The share of power plants amounts to 6,000 t (0.25 %) (www.umweltbundesamt.de/emissionen/archiv, as of 15. Sept. 06). 151 10.4 Nitrous Oxide Emissions

For 2000, the global N2O emission from stationary combustion plants is estimated to be 213,000 t (0.2 Gg) (EPA 2001) and thus contributes to approx. 7 % of the total emission of the industrialised countries. Within the EU-15, N2O emission has decreased by 18 % from 414 to 340 million tons (Tg) for the period between 1990 and 2004. EEA (2006) reports the contribution of the public electricity and heat industry to be 4 %. The trend of nitrous oxide emissions in Germany shows a decrease by over 24 % from 273,000 t to 207,000 t for the period between 1990 and 2004 (NIR 2006). With 12,500 t, the share of power plants and CHP plants amounts to around 6 % (www.umweltbundesamt.de/emissionen/, as of 15 Sept. 06). Compared to Fig. 10.11, the data was corrected by UBA (as of 2002).

Fig. 10.11: Trend of nitrous oxide emissions in Germany between 1990 and 2000 (Agriculture and waste industry, Industrial processes/use of products, traffic, Domestic households/small consumers/industrial firings/power plants and CHP (Umweltdaten 2002, UBA)

10.5 Ozone Emissions Ozone is not directly emitted but is formed in the troposphere mainly by reactions with nitrogen oxides, methane, carbon monoxide and volatile organic compounds (NMVOC). In Ger- many, these substances were strongly reduced in the last years.

10.6 Nitrogen Oxide Emissions

According to IIASA (2006), with 81 million tons NO2 emissions deriving from the combustion of fossil fuels (globally) remained more or less constant for the period between 1990 and 2000. Around one quarter proceeds from the combustion of fossil fuels. The clear reductions achieved in Europe and North America were levelled out by the increases in Asia (Richter 2005). NOx emissions in the EU-15 were reduced by 31 % from 13 million t to 9.2 million t for the period between 1990 and 2004 (EEA 2006). 152

Fig. 10.12: Trend of NOx emissions in Germany according to consumer groups (power industry, traffic, industrial processes, processing industry, domestic households and small consumers, agriculture) from 1990 to 2003 (UBA 2005) (http://www.env-it.de/umweltdaten/public/document/downloadImage.do?ident=7368)

For the period between 1990 and 2004, NOx emissions in Germany were reduced by 45 % from 2.9 million t to 1.6 million t (NIR 2006, EEA 2006). Already since the 1980s, German industry has drastically been reducing its nitrogen oxides emissions. With 276 kt, the share of power plants still amounted to around 17 % in 2004 (traffic with approx. 50 %) (www.umweltbundesamt.de/emissionen/, as of 15 Sept. 06). Data in Fig. 10.12 was slightly corrected by UBA.

10.7 Emissions of Volatile Organic Compounds without Methane (NMVOC) According to IPCC (2001), in the mid 1980s, around 571 million t VOC were emitted globally (calculated as C). The anthropogenic share amounts to around 33 %. In the EU-15, NMVOC emissions decreased by 42 % from 15.3 million t to 8.9 million t for the period between 1990 and 2004 (EEA 2006). In the same period, NMVOC emissions in Germany were reduced by two thirds from 3.6 million t to 1.2 million t (NIR 2006). Today, the main share with around 60 % is attributed to the use of solvents. With 8.5 kt (0.7 %), the share of power plants and CHP plants is very small (www.umweltbundesamt.de/emissionen/, as of 15 Sept. 06). Data in Fig. 10.13 (as of 2002) was slightly corrected by the UBA.

153

Fig. 10.13: Emission trend of volatile organic compounds without methane (NMVOC) in Germany 1990 – 2000 (solvent use, winning and distribution of fuels, traffic, industrial processes/domestic households/small consumer/ industrial firings/power stations and CHP) (Umweltdaten Deutschland 2002, UBA)

10.8 Carbon Monoxide Emissions According to IIASA (2006), worldwide carbon monoxide emissions proceeding from the combustion of fossil fuels slightly decreased by approx. 4 % from 492 million t to 470 million t between 1990 and 2000. The considerable reduction by 36 % in Western Europe contrasts to a clear increase in Asia and Africa. In the EU-15, CO emissions were halved from 51.3 million t to 25.5 million t for the period between 1990 and 2004 (EEA 2006). In the same period, it was possible to achieve a reduction by two thirds from 12.1 million t to 4.1 million t in Ger- many. With 3 % (134 kt), the share of power plants and CHP plants is small. With 41 %, traffic has the main share (www.umweltbundesamt.de/emissionen/, as of 15 Sept. 06).

10.9 Sulphur Hexafluoride Emissions

In 2002, the worldwide SF6 emissions amounted to around 6000 t. Within the EU-25, SF6 emissions were reduced by 40 % from 700 to 390 tons for the period between 1995 and 2004 (EEA 2006). Despite an increase in stocks of SF6 operating media, it was possible to reduce SF6 emissions by around 40 % at European level for the last 10 years due to voluntary measures taken by manufacturers and operators (Ecofys 2006). With 25 t, SF6 emissions deriving from electrical media were the third biggest emission source after its use for soundproof windows (48t) and for the purification of aluminium (45 t) in Germany in 2003. The use in car tyres was drastically reduced. Due to a voluntary declaration of the ZVEI and the VDEW in 1997 and its further amendment (ZVEI 2005), a clear emission reduction by around 50 % (2005) for switch gears and converters could be reported for the period since 1995. This was achieved by reducing losses in plants, during construction and due to leakages during operation. In Germany, total emissions amounted to 187 t in 2004, compared to 302 t in 1995 (Schwarz 2004) and to 200 t in 1990.

10.10 Sulphur Dioxide Emissions Sulphur dioxide is not a greenhouse gas but a precursory substance of climate-relevant atmospheric sulphuric acid aerosol. According to IIASA (2006), worldwide SO2 emissions by the combustion of fossil fuels were reduced by 18 % from 122 million t to 103 million t for the period between 1990 and 2000. The decrease was achieved by emission reducing measures particularly in Western Europe and North America, and by structural changes in Eastern Europe. Clear increases occurred mainly in Asia. Within the EU-15, SO2 emissions decreased by 70 % from 15.5 million t to 5.0 million t for the period between 1990 and 2004 (EEA 2006). In Germany, the reduction was even heavier with nearly 90 % from 5.3 million t to 575,000 t. The contribution of the power plants in Germany was also reduced by 90 % 154 from 3.1 million t to less than 317,000 t (www.umweltbundesamt.de/emissionen/, as of 15 Sept. 06) (Fig. 10.14 for 1990 – 2003).

Fig. 10.14: Trend of sulphur dioxide emissions in Germany between 1990 and 2003 (power industry, traffic, diffuse emission of fuels, processing industry, domestic households and small consumers, industrial processes) (UBA 2005, http://www.env-it.de/umweltdaten/public/document/downloadImage.do?ident=7370)

10.11 Emissions of Fine Dust Fine dust particles are mainly aerosols and are emitted by manifold sources. The fine dust emissions in the EU-15 were reduced by 39 % between 1990 and 2002 (http://themes.eea.europa.eu/IMS/IMS/ISpecs/, as of 13 Oct.06). In Germany, the total dust emission was reduced by more than 90 % from 2,628 kt to 237 kt for the period between 1990 and 2004. In this period, the power plants and CHP plants were also able to strongly reduce their dust emissions by 99 % from 1,330 kt to 12 kt by decommissioning old power plants and improving dust separation. Within the same period, fine dust emissions (PM10) were reduced from 1,330 kt to 12.2 kt. The share of the power industry (public power plants and industrial power plants) was also reduced by 99 % from 1,178 kt to 11.7 kt, according to Umweltbundesamt (Federal Environment Agency) (www.umweltbundesamt.de/emissionen/publikation/ as of 15 Sept. 06). 155

11 Geoengineering and Reforestation The term geoengineering describes attempts to intentionally change nature on a planetary scale (Keith 2003). The intention is to reduce or avoid the influence of the anthropogenic greenhouse effect. Already in 1982, the Russian meteorologist Budyko proposed to reduce the greenhouse effect by artificially introducing sulphate aerosols into the stratosphere which would lead to a cooling. The proposal to introduce sulphate aerosols into the stratosphere in order to compensate climate warming was again brought into discussion by Crutzen in 2006. Another proposal was to change reflection (albedo) by placing swimming, reflecting particles onto the sea surface (USA 1965). A further idea was the installation of huge sunshades in space which were said to change the proportion of solar radiation and with this also the solar constant. In 1997, Edward Teller and colleagues presented such a "sunshade" which was to be installed in space between the Earth and the Sun (Teller 1997). It was intended to deflect solar radiation in order to selectively warm the atmosphere or the terrestrial surface. All these possibilities constitute a significant risk for our climate system, and according to our knowledge today, they will probably not be used (Keith 2003). Nevertheless, in an extensive "Global Climate & Energy Project" (GCEP), Standford University is also concerned with this topic (http://gcep.stanford.edu/research/geoengineering.html). On a smaller scale, attempts to control the weather had been made since even the 1950s, by inoculating clouds. In order to avoid the formation of tropical cyclones it was considered to bring an oil film onto the sea surface to impede water evaporation and thus the intake of energy. Yet, perspectives for success were estimated to be small because the waves would quickly destroy the oil film.

11.1 Fertilising with Iron in order to Increase Growth of Algae

There are considerations for stimulating the growth of algae, and with it the CO2 assimilation of the oceans by fertilising the sea with iron dust (Fig. 11.1). Around one half of the carbon dioxide assimilated by plants worldwide is contained in plankton algae in the sea. Around one fifth of the oceans are areas with iron deficiencies, particularly in the South Polar region. In 2000, 2002 and 2004, the Alfred-Wegener-Institut (AWI) carried out several concrete experiments with great success (EIFEX-Experiment). The growth of algae in the fertilised areas increased drastically for a short time.

Fig. 11.1: Fertilisation of the sea with iron in order to reduce CO2 by increasing the growth of algae (Kasang, HBS 2005) It is not yet known how big the amount of dead plankton is which sinks into oceanic depths and thus actually withdraws carbon from the biosphere. Also expected secondary effects on the oceanic biochemistry and the composition of algae populations are not quite clear yet. Model calculations have shown that theoretically up to 15 % of the current anthropogenic carbon dioxide emissions could be reduced by the largest possible iron fertilisation (Chisholm 2001, Keith 2003, Smetacek, V. 2004, Engel 2004). Markels and Barber (2001) assume the costs for this CO2 sequestration to amount to approx. 7 $/t C (Ploetz 2002). 156 11.2 Reforestation Reforestation can bind considerable amounts of carbon in the biomass of the forests. The forest photosynthesis withdraws carbon dioxide from the atmosphere and permanently includes the carbon contained in it in the plant mass (mainly wood, roots). The carbon assimilated in biomass is released again into the atmosphere during the decomposition process of dead biomass. If decomposition of plant masses prevails, the forests are a carbon source. However, if plant masses are built up, they act as carbon sinks. At present, 20 to 25 % of the anthropogenically caused carbon dioxide emissions originate in the irregular use of forests, particularly clearings. By well-directed measures in the area of forestry and wood industry, it is possible to reduce the increase in atmospheric CO2 emissions. The following possibilities are at hands: - Reforestation - Measures for the maintenance of woods - Improved methods for its cultivation - Substitution of fossil fuels - Substitution of materials produced with high energy input by wood The Kyoto Protocol permits the industrialised countries to reduce part of their carbon dioxide emissions by reforestation in developing countries. This way, the carbon dioxide produced during the combustion of fossil fuels is assimilated by newly planted forests e.g. in the tropics. There have been long discussions about the question whether it is possible to credit forestry activities and changes in the use of land. Disputed was the question of verification and measurability of the storage success and the danger of reversibility which generally exists for storage projects: forest fires and complete deforestation at later times could quickly destroy all achieved success. Therefore, the IPCC Special Report "Land Use, Land-Use Change“ (LuLuCF) which was published in 2000, contains proposals for the definition of sink catego- ries and emission allowances within the framework of the Kyoto mechanisms Joint Imple- mentation (JI) and Clean Development Mechanism (CDM). The 2001 UN conference in Mar- rakech (COP 7) decided that sinks, that is to say carbon-binding activities in forestry and agriculture, may be credited instead of a corresponding reduction of emissions. This reduces the reduction quota by approx. 1.8 % for all industrialised countries. In 2003, at COP 9 in Mi- lan, special directives were adopted for the acknowledgement of forestry and reforestation programmes within the framework of CDM (see ISI Leitfaden Klimaschutz chapter 5).

11.3 Tillage Since it has only been known for a few years that soil retains considerable amounts of carbon, it was examined how to increase the retained amount or how to avoid its release due to cultivation. Measurements have shown that the soil retains twice the amount of carbon than plants (in the case of agricultural soils even up to 98 %), and that adequate tillage may reduce the release of carbon dioxide. So-called blade cultivators till the soil shallowly and broadly. In contrast to a plough, the plant material on the soil, like straw, is not worked too deeply into the soil and thus, it can turn to humus more quickly. With this, more carbon is retained in the soil. This procedure is already commonly being used for 70 % of the agricultural surfaces in the USA, in Germany only for 6 % (Keith 2004).

157 12 Carbon Dioxide Reductions in the Power industry Worldwide, the power industry contributes to energy-attributable emissions of the climate gas CO2 with approx. 32 % (www.mnp.nl/edgar). Industry increasingly strives to contribute to the reduction of its emissions. To this end, a broad portfolio of energy production technologies including fuel switching (coal/oil to gas), increased power plant efficiency, and increased use of renewable energy technologies (e.g., biomass, solar, wind, hydropower, geothermal, etc.) and nuclear power is currently available. Additionally, there is an intensive research concerning the carbon capture.

Long-term options for a power generation free of CO2 emissions Renewable power generation Nuclear energy

Fossil fuels with CO2 capture and storage

Mid-term potential of CO2 reduction Improvement of the efficiency at fossil fired power plants Improvement of the renewable energy input (precondition: drop in costs) Nuclear energy (precondition: acceptance)

Fig. 12.1: Long-term and medium-term options for a carbon dioxide reduction (source: Engelhard, RWE 2005 (http://www.deklim.de/download/rheinklima/05_Engelhard.pdf))

12.1 Efficiency Improvement Since the beginnings of power plant technology, the power plant engineer has constantly been entrusted with the task of increasing efficiency – originally for mere economic reasons in order to save fuel costs, and for the last 30 years, increasingly for environmental and climate protective reasons. The success in improving efficiency achieved in the last years is shown in an exemplary way for lignite-fired power plants in Figure 12.2.

Fig. 12.2: Development of the net efficiency of lignite-fired power plants rising from below 30 % to approx. 45 % between 1960 and 2005 (Engelhard 2005)

In the past 30 years, the efficiency of fossil-fired power plants has increased from 31 % to 36 % on a global average. The top values of modern plants amount to 47 % (coal-fired steam 158 power plants) (RWE Weltenergiereport 2005). This was made possible by increasing the vapour states and by further developing the steam turbine technology and the power plant process. The gas and steam turbine technology allowed for an efficiency increase from 40 % at the beginning of the 1980s to 58 % (without use of heat) for gas-fired combined-cycle turbine power stations. The average specific CO2 emissions of all fossil-fired power plants in Germany decreased by approx. 8 % from 932.6 g CO2/kWh to 858.2 g CO2/kWh for the period between 1992 and 2003. Within the next 15 to 20 years, requirements for renovation of fossil-fired power plants in Germany will amount to at least 20 % (40,000 MW) of the existing plants (Fischer 2006). By 2030, this programme for the construction of new plants with higher efficiency would result in a 10 to 20 % reduction of CO2 (Fischer 2006, RWE 2006). Due to further developments of processes and components, like double reheating and supercritical vapour states, as well as fluidic improvements of turbines, efficiencies of up to 53 % may be expected by 2020. R&D programmes supported by the EU are in progress (e.g. the VGB initiative: Emax Power Plant Initiative, www.comtes700.org). With the Comtes 700 project, nine European energy suppliers (RWE, E.ON, EnBW, Vattenfall, EDF, Electrabel and others) want to test critical power plant components for the temperature range of 700 °C. This 700-degree technology could reduce CO2 emissions by 30 % (RWE 2006). According to Fischer 2006, the mere increase in efficiency by around 5 % for all power plants around the world would save around 1 billion t carbon dioxide (Fig. 12.3). This shows the enormous savings potential by improving efficiency.

Total amount of power plants in Germany Regional reduction potential of a 5% increase currently approx. 5% below technological in efficiency worldwide state of the art

Fig. 12.3: Comparison of the efficiencies of power plant installations worldwide left side). If efficiency was globally increased by 5 % it would be possible to save 1 billion t carbon dioxide (right side) (Fischer 2006)

While CO2 emissions by the power plants of the utility companies decreased only slightly from 289 million t to 286 million t due to the increased power demand in Germany for the period 1990 to 2003, the specific emission was reduced by approx. 10 % from 670 g/kWh (net) to 600 g/kWh (net) (Fig. 12.4).

159

Fig. 12.4: Trend of the specific CO2 emissions of German utility power plants, fossil energy mix (upper value) and total energy mix in kg/kWh (net) between 1990 and 2003 (VDEW 2005)

12.2 Renewable Energies The worldwide capacity for energy generation from renewable energies amounted to approx. 160 GW in 2004 (without big hydropower). That is 4 % of the globally installed total power of 3800 GW. With 2700 TWh, big hydropower (720 MW) generated 16 % of the global energy production of 16,328 TWh in 2004, wind energy 95 TWh (0.6 %), electric current from biomass 150 TWh (0.9 %), small hydropower 240 TWh (1.4 %), geothermal electric current 60 TWh (0.4 %) (BMU Globaler Statusbericht 2005). Within the last years, wind energy had high increase rates of 28 % (48 GW installed worldwide in 2004) and photovoltaics of 60 % (4 GW installed worldwide in 2004), although it contributed to only 0.1 % of the global power generation (Fig. 12.5). In 2004, the following capacities (GW) in renewable energies were installed worldwide:

Big hydropower 720 GW Small hydropower 61 GW Wind power plants 48 GW Electricity from biomass 39 GW Geothermal electricity 8.9 GW Photovoltaics (PV), grid-independent 2.2 GW Photovoltaics (PV), grid-connected 1.8 GW Solar thermal electricity 0.4 GW Ocean (wave) energy 0.3 GW

160 (BMU 2006a, Globaler Statusbericht Erneuerbare Energien, Global Status Report Rene- wable Energies 2005) (Around the globe, there are different definitions for big hydropower: from 2.5 - 50 MW, often 10 MW)

Fig. 12.5: Globally installed capacity of renewable energies, developing countries, the EU-25 and five leading countries in 2004 (BMU Globaler Statusbericht 2005)

Within the EU-25, in 2004, around 15 % of electricity was generated from renewable energies, and 31 % from carbon dioxide-free nuclear energy.

Fig. 12.6: Trend of the share of renewable energies in Germany for 1990 – 2005 (BMU Statistics 2006)

According to BMU (2006), with 17,574 wind power stations, wind energy contributed the biggest share to power generation from renewable energies in Germany in 2005 (approx. 26.5 billion kWh), followed by hydropower (approx. 21.5 billion kWh) and biomass (around 13.1 161 billion kWh) (Fig. 12.6). Compared to the previous year, particularly power generation from biogas increased (by around 2 billion kWh). Energy from wind energy increased by approx. 1 billion kWh, and from hydropower by around 0.5 billion kWh. The production of solar energy doubled to approx. 1 billion kWh. So far, geothermal energy production does not play a role in Germany (2005: 0.0002 TWh). (http://www.erneuerbareenergien.de/files/english/renewable_energy/downloads/application/p df/broschuere_ee_zahlen_en.pdf)

Figure 12.7 shows the share of renewable energies in the electricity, in Germany for 2005. Wind energy has now surpassed hydropower.

Fig. 12.7: Breakdown of electricity in 2005 generated from renewable energies in Germany (BMU statistics 2006) According to BMU (BMU statistics 2006), the increase in renewable energies continued to enhance in 2005. In 2005, a total of approx. 62.5 billion kWh electricity was generated, compared to 57.4 billion kWh in 2004. Thus, the share of renewable energies increased from 9.4 % to 10.2 %. The capacity increase of wind power plants amounted to 1,808 MW, and of photovoltaics to approx. 600 MWpk (pk = peak capacity). Electricity generation from biogas increased from 1.4 billion kWh in 2004 to 3.2 billion kWh in 2005. The German Government has the objective to increase the share of renewable energies in the total energy consumption from currently 4.6 % to at least 10 % in 2020 (BMU 2006c). For electricity, at least 20 % are to be attained (Fig. 12.8). According to the BMU, renewable energies in the electricity sector avoided around 57.5 million t carbon dioxide in 2005 (Staiß 2006) (all sectors: 83 million t). According to an expertise by the ISI (2005), the use of renewable energies saves an average of 924 g CO2 per generated kWhel in Germany. On February 2007 published provisional values for 2006 show a further increase in renewable energies in Germany from 10.4 % 2005 to 11.8 % 2006: Total 72.7 billion kWh, (wind 30.5 billion kWh, hydro 21.6 billion kWh, biomass 13.1 billion kWh, biogas 5.4 billion kWh, Photovoltaic 2 billion kWh). Wind energy has now a share in total electricity consumption of around 5 %. End of 2006 18,685 plants were installed with a capacity of 20,622 MW, 2,233 MW more than 2005. (http://www.erneuerbareenergien.de/files/pdfs/allgemein/application/pdf/hintergrund_zahlen2006_eng.pdf) 162

Fig. 12.8: Capacity trend in the power supply from renewable energies (hydropower, wind, photovoltaic, biomass, geothermic, import) until 2020 according to estimations by recent studies (BMU-Statusbericht 2006)

By the end of 2005, 11 offshore wind farms with around 780 wind turbine generators had been approved for the North Sea (10) and Baltic Sea (1) ( http://www.bsh.de/de/Meeresnutzung/Wirtschaft/Windparks/index.jsp). 45 km off the coast at Borkum, a joint project company of E.ON, Vattenfall and EWE will install an offshore wind farm with a total of 12 wind turbine generators of the 5 Megawatt class by 2008 at the latest. Up to today, in Germany there are 24 hydrothermal heating plants with a total heat capacity of 700 MW, and one geothermal pilot plant in Neustadt-Glewe in Mecklenburg-Vorpommern which also generates electricity (200 kW power) (www.geoscience.online.de). According to different studies and statements, a significant increase in renewable energies is planned by 2020 (Fig. 12.8) (BMU Statusbericht 2006). This will require investments of around 75 billion €. On 8 of March 2007, the European Union has reached a comprehensive agreement on its climate and energy policy:

• By 2020, CO2 emissions across Europe are to be cut by 20 percent as compared to 1990 emissions. • Renewable energy sources are to make up 20 percent of the EU's energy mix by 2020 -- up from their current 6.5 percent share.

12.3 Nuclear Energy In 2005, nuclear power plants generated around 16 % of the global power demand. In 2005, 442 nuclear power plants (370 GW) operated in 31 countries and generated approx. 2,626 TWh of electricity (http://www-pub.iaea.org/MTCD/publications/PDF/RDS2-26_web.pdf). (2006: 435) Compared to coal-fired power plants, emissions of up to around 2.6 billion t CO2 have been avoided. In Europe (EU-25), in 2005, 204 nuclear power plants in 18 countries produced 973 TWh or 31 % of the power demand and saved the environment of annually more than 900 million t carbon dioxide. With 159 billion kWh, the 17 nuclear power plants in Germany had a share of approx. 27 % in the power generation in 2006. According to reports by the VDEW, they avoided up to 159 million t CO2 in 2006. 30 reactors are under construction in 11 countries (most in Asia) today. In all, over 60 power reactors with a total net capacity of nearly 70,000 MWe are planned and over 150 more are proposed (2/2007, http://www.world-nuclear.org/info/inf17.html). In Europe, a new nuclear power plant is under construction in Finland, and a plant is planned in France. China is plan- ning the biggest increase from currently 6,500 MWe up to 40,000 MWe by 2020. In the USA, 19 plants are planned with a total of 21,000 MWe (http://world-nuclear.org/info/inf41.htm). IAEA now anticipates at least 60 new plants in the next 15 years, making 430 GWe in place 163 in 2020 - 130 GWe more than projected in 2000 and 16% more than actually operating in 2006.

12.4 Emissions Trading With the Kyoto Protocol, the participating industrialised countries committed themselves in 1997 to reduce the emission of climate damaging gases, like carbon dioxide, by 5.2 % for the period between 2008 and 2012, compared to 1990. The European Union promised to reduce its emissions by 8 % between 2008 and 2012, compared to the 1990 level. In order to achieve this objective, the member states committed themselves to achieve national climate protection targets within the framework of burden sharing. Germany promised to reduce its greenhouse gas emissions by 21 % in the same period. Yet, it has to be observed that fulfill- ing the Kyoto targets - calculated up to 2050 - will only lead to a minimum reduction (less than one tenths of a degree) compared to the otherwise occurring temperature trend (BMBF 2003). Within the implementation of the Kyoto Protocol, the emissions trade started in the European Union on 1 January 2005. On the basis of the emissions trade directive which came into force in October 2003, the EU member states are obliged to adopt national allocation plans in order to practice emissions trade. Furthermore, the Linking Directive connects the project- centred flexible Kyoto mechanisms (CDM, JI) to the emissions trading scheme of the EU. Eu- ropean companies covered by the EU emissions trading system will be allowed to convert credits from JI and CDM projects for use towards meeting their commitments under the trading system.

Fig. 12.9: Principle of the emissions trading scheme (from: Fichtner: http://www.co2-info.com/principle_of_the_eu_ets.html)

The emissions trading scheme is designed to create an economic basis for the reduction of the detrimental climate gas CO2 at those places where it is most cost-effective. Concrete reduction targets were allocated to the individual economic sectors and each concerned installation, and emission allowances were accordingly issued free of charge on 30 September 2004 for 499 million t CO2 for the first trading period. The allowances may be traded and thus serve as a kind of currency. If the company achieves the targets by its own cost-effective CO2 reducing measures, allowances the company did not need may be sold on the market. 164 Alternatively, if it does not dispose of its own allowances, it has to buy them on the market. If the company does not meet its reduction targets (CO2 reduction or acquisition of allowances), sanctions will be taken which amount to 40 Euro for each ton carbon dioxide within the first trading period, and the reduction obligation which was not met must be met in addition in the following year - if necessary, by acquiring further allowances. The principle of the emissions trading scheme is shown in Figure 12.9.

Allocated Amounts and Included Plants in the EU and Germany Within the enlarged EU-25, 11,428 energy generating and energy intensive plants have the obligation to participate in the emissions trade. They are responsible for nearly half of the CO2 emissions in Europe. In bigger member states, 1,000 to 1,850 installations are included, in most of the remaining member states, the covered installations generally amount to between 50 and 400. In Germany, 1,849 installations have the obligation to participate in the emissions trading. Especially all the big firing plants are among them. According to estimations by the BMU (2005), in Germany around 98 % of the emissions proceeding from the electricity and district heating industry and more than 60 % of the industrial emissions are covered by the emissions trading scheme (http://www.emissionshandel-fichtner.de/). Since 01 Jan. 2005, the German emissions trading system is regulated in the Greenhouse Gas Emissions Trading Act (TEHG). The act, which came into force on 30 Sept. 2005 and which introduced project-related mechanisms (ProMechG) pursuant to the Kyoto Protocol, creates the national basis for issuing allowances for emission reductions which are created by projects within the framework of Joint Implementation and Clean Development Mechanism. Ac- cording to this system, emission allowances proceeding from CDM projects may be credited as of 2006, and those proceedings from JI projects as of 2008, to the obligations for the sale of emission allowances.

Schedules 01.2005 Start of the EU emissions trading scheme For the first time, the companies concerned have to present a verified 03.2006 emissions report Publication of the new National Allocation Plan for the second trading 06.2006 period 2008-2012 12.2007 End of the first trading period 04.2008 Final account for the trading period 2005-2007 01.2008 Start of the second trading period 2008 – 2012

The BMU and Fraunhofer Institute for Systems and Innovations Research developed a guide for companies concerning the Kyoto mechanisms like the emissions trading scheme (EH), Joint Implementation (JI), Clean Development Mechanism (CDM) which may be downloaded from the internet (http://www.isi.fraunhofer.de/n/druckversion072005.htm) The German Emissions Trading Authority (DEHSt) at the Federal Environment Agency draws positive conclusions one year after the introduction of the emissions trading scheme: Since March 2005, more than 90 million emission allowances have been transferred, this is 18 % of the issued allowances. Trade also worked via the European Central Registry (CITL), around 21 million emission allowances were transferred abroad, and 19 million emission allowances came to Germany from abroad (Presseinformation UBA 077/2005). In the first half of 2005, the prices amounted to 7 € and then partly rose to 27 € for emission allowances (RWE Weltenergiereport 2005). On May 2006 the prices fall to 15 €/t (DNK 2006). The power industry particularly criticises the retarded start of the emissions trading system which was due to problems with the opening of the accounts at the Emissions Trading Au- thority (DEHSt) in the spring of 2005, and the retarded allocation of emission allowances in 165 other European countries. In addition, the allocated amounts were clearly smaller than expected, particularly for the energy sector. Many proceedings of objections are still pending. Fischer, EON (2006), demands a simplification of the allocation procedure, possibly without special regulations. Vattenfall (2006) numbers three basic weak points of the European trading scheme: Firstly, only the period 2008 to 2012 is defined, secondly, it is limited to the EU and thus reduces the competitiveness of the European industry, and thirdly, the present system covers less than 50 % of the total CO2 emissions in the EU-25. EnBW filed a case with the European Court of Justice against the provisions for the transfer of old installations, and continues to object it in its statement about the NAP II: (http://www.bmu.de/files/emissionshandel/gesetze_und_verordnungen/application/pdf/nap_st ellungnahme_enbw.pdf ) On February 2007 the Federal Environment Ministry of Germany (BMU) reviews the National Allocation Plan. Revised NAP II based on secure data: Minus 34 million tones of C02 to 462 + 3 million tones (- 6.8%). According to BMU, Germany will now definitely meet the climate protection targets of the Kyoto Protocol (minus 21% by 2012 compared to the base year 1990; current status: approximately – 19%). 12.5 Carbon Dioxide Capture and Storage (CCS)

In addition to a continued improvement of efficiencies and a shift to fuels reduced in CO2 emissions, also possibilities for the CO2 capture and storage (CCS = Carbon Capture and Storage) are being examined, since the biggest part of the CO2 emissions proceeds from the combustion of fossil fuels. A special report published by IPCC 2005 (Special Report 2005) has shown that around 20 to 40 % of the worldwide carbon dioxide emissions could be captured and stored at "acceptable" costs by 2050. The Federal Ministry of Economics (BMWA) also published a study on CO2 reducing technologies (COORETEC, development concept for low-emission fossil-fired power plants, 2003, www.cooretec.de) which shows the way towards low-emission fossil- fired power plants and, in the long term, even plants free of emissions. Its objective is to limit the costs of retention to approx. 20 to 30 US$/t CO2 by 2020 and to simultaneously increase the efficiency to 53 % for coal and to 61 % for gas. Also the EU Commission wants to focus on Clean Coal Technologies for its research promotion (www.euro-cleancoal.net).

Fig. 12.10: The three main options for the carbon capture in power plants: (above) carbon capture after combustion, (centre) improved carbon capture due to the combustion of oxygen instead of air, (below) carbon capture before combustion with IGCC (source: VGB 2005) 166 Different worldwide research and development projects accelerate the progress of the carbon capture for its application. With its Clean Coal Power Initiative (CCPI) started in 2001/2002 and its 2 billion US$ funding for a 10-year R&D programme, particularly the USA are leading in this field (www.netl.doe.gov/technologies/carbon_seq/). On behalf of a whole range of research projects in Europe, the research and development project EnCap/SP3 (Enhanced Capture technologies) is presented, with 30 companies and universities participating in it and with a budget of 30 million Euros. The German Federal Ministry of Economics is promoting the German project Cooretec for the period between 2005 and 2008. Basically, there are three options available for the carbon capture in power plant processes which are described in Fig. 12.10 and in chapter 12.5.1.

12.5.1 CO2 Capture

All capture processes have in common that after its capture and enrichment, CO2 has to be dehydrated and compressed for transport.

Carbon Capture after Combustion (Post-Combustion)

Due to the fact that CO2 is present in the flue gases only in a very thin form because of the high fraction of air nitrogen (low partial pressure) rooted in current combustion technologies - combustion of carbon with air - it is very complicated to capture carbon dioxide from the flue gases. In the post combustion process, CO2 is extracted from the flue gas by means of a CO2 gas separation procedure with capture rates of over 90 %. The only capture process in question at present is chemical absorption. In an absorption column, CO2 is withdrawn from the flue gas by means of an adequate absorbent like monoethanolamine (MEA). CO2 dissolved in the amine solution is extracted from the amine by thermal absorption and separated in high concentrations. In contrast to the procedures described below, this procedure interferes least with the power plant processes and thus is the most adequate one for the subsequent retrofitting of existing power plants (DPG Studie 2005).

Combustion with Oxygen (Oxyfuel Process) In the oxyfuel process, the combustion occurs with pure oxygen in order to reduce the nitrogen in the flue gas and to produce nearly pure CO2. In order to reduce the high combustion temperatures connected to it, the already cooled flue gas is transported back into the combustion chamber. By condensing the water, the CO2 can be separated from the CO2/water vapour mixture. The development of a gas turbine, which is designed to use the produced CO2 as turbine operating medium before it is finally liquefied or mineralised, is also considered to be an innovation for power generation. An air separation plant is necessary for the oxyfuel process (technological state of the art); however, it is being examined how to develop oxygen-permeable membranes at lower costs which separate oxygen from the air. At the end of May 2006, the construction of the first worldwide oxyfuel pilot plant with lignite firing (30 MWth) was started by Vattenfall in Spremberg (Schwarze Pumpe) (startup in 2008) (http://www.vattenfall.de, Strömberg 2003, 2004).

Carbon Capture before Combustion with IGCC (Pre-Combustion) In this procedure, the fuel coal is firstly converted into gas in an IGCC power plant (Inte- grated Gasification Combined Cycle), and the CO formed in this process is converted into H2 and carbon dioxide with water vapour. Afterwards, the main components CO2 and H2 are separated. Then, the hydrogen is burnt in a gas turbine, and a subsequent waste heat boiler generates vapour for the steam turbine. On a global scale, five gasification demonstration power plants are already operating, but they are still subject to availability problems and high investment costs (VGB 2005, DPG 2005). Together with project partners (Projekt ENCAP), RWE is intensifying the research at a combined power plant with integrated coal gasification and CO2 separation. Additionally, RWE plans to commission a large-scale technological plant with 400 - 450 MW by approx. 2014 (www.rwe.com/kraftwerk/igcc-kraftwerk/). 167 At present, all three separation concepts have in common that they require extensive additional equipment with considerable efficiency losses of around 8 to 13 % points for the power generation. Since many procedures are still at a very early stage of development, technical- commercial data are available only to a very limited extent, and they are subject to great uncertainties.

12.5.2 Transport of Captured CO2

After its capture, CO2 is compressed and liquefied for transport and storage. For economic reasons, there are only two methods available for the transport of the captured CO2:

Transport per Ship The carbon is transported in liquefied form. It is possible to fall back on experience with the transport of liquefied gases. It is necessary to install intermediate storage capacity for the CO2 supplied from the power plants.

Transport in Pipelines

To this end, CO2 is transformed into its supercritical stage before transporting it (> 73 bar, generally, pressures of > 100 bar are used). As far as the transport in pipelines is concerned, there is already some knowledge available, particularly from USA.

12.5.3 Storage

A number of possibilities are being discussed and tested for the storage of captured CO2 (Fig. 12.11)

Storage in Geological Formations

To this end, the CO2 is discharged in aquifers - in general, layers of porous rock containing saline water - or in oil or natural gas fields which are no longer economical to use, or also in coal ledges. The discharge into oil or natural gas fields may drive out additional oil or natural gas, and in the case of coal ledges, methane may be discharged. The capacity of saline water aquifers is considerably high and amounts to hundreds and thousands of giga tons of CO2 (DPG-Studie 2005). For several years, Statoil (Sleipner Project) has been practising this procedure in the North Sea on a large scale. Further projects exist in Canada, Algeria and USA (SRCCS 2005). The CO2 storage project CO2SINK of the GFZ (National Research Centre for Geosciences in Potsdam) is to be carried out in Ketzin, Brandenburg, with EU funding. Within the RECOPOL project, which is also EU-funded, up to 20 t carbon dioxide are to be pressed a thousand metres deep into coal ledges of the Silesian coal basin in Poland on a daily basis, starting in 2006. Next to the technical feasibility, the economic feasibility is also to be examined. Sea Storage

For storage in the sea, CO2 is either introduced in average depths of 1,000 to 2,000 m in liquefied form in order to mix with the sea water, or it is introduced at a depth of 3,000 m where it sinks to the seabed due to its higher density compared to the sea water. Owing to ecological doubts and missing public acceptance, CO2 storage in the sea seems to be a very ques- tionable option. WBGU (2006) declared that it opposed sea storage.

Storage as Carbonate

This way of storage is designed to bind CO2 as carbonate by its reaction with silicates, mainly magnesium silicate. The mineral necessary for it is available worldwide in sufficient amounts and may be extracted in opencast mining. The big mass flows which must be moved in order to bind and transport the CO2 separated in the power plant, as well as the high energy consumption, are significant disadvantages of this method. Therefore, the mineralised capture of CO2 seems to be a less valuable solution compared to the alternative possibilities for the CO2 storage. 168 :

Fig. 12.11: Scheme of different possibilities for storage of carbon dioxide separated in the power plants with an indication of amounts (technical potential) (source: lecture Metz 2005)

12.5.4 Conversion/Use of CO2

There are also several possibilities for the conversion/use of CO2, although these options offer only a very limited potential for use. One possibility of the industrial conversion/use is the use of CO2 for the synthesis of technical substances. Among them, there is e.g. the urea synthesis or the methanol synthesis. So far, the majority of the above-mentioned procedures is developed only theoretically or is still in the initial phase of their testing. Many questions - also of non-technical character - are still not answered, e.g. the question of approval in the case of a geological CO2 storage, of security, and, which is most decisive one, of the duration of the CO2 occlusion. 169

12.5.5 Cost Estimate

Cost estimates for capture, transport and storage of CO2 vary considerably from 20 to 60 €/t of avoided carbon dioxide (VGB PowerTech, 2004). The major share in it (around 15 to 40 €/t) is due to the CO2 capture. For the lignite power plant with oxyfuelling, Vattenfall calculates an efficiency loss of 8.7 % (Strömberg 2004). The Cooretec working group in Germany estimates the costs for transport and storage to amount to around 10 to 24 € per ton CO2 (Cooretec 2003) (0.8-2.0 € Cent/kWhel). IPCC Special Report, SRCCS (2005), reports an increase in power generation costs for the carbon capture including transport and storage to amount to between 21 and 91 % in the range of 0.043 to 0.099 US$/kWh, depending on installation and fuel. The costs for one avoided ton carbon dioxide would amount to 14 to 91 US$. Although a lot of theoretical and practical research has been conducted - in some cases for years - or is being conducted, neither the capture nor the storage of CO2 will be regarded as state of the art in the near future, that is to say, within the next 10 to 15 years. Upshot: The decisive criteria for the large-scale introduction of Clean Coal Technologies will be the connected costs for avoiding CO2, compared to alternative technologies for avoiding CO2. The cost estimates which exist so far show that despite the additional costs for the CO2 separation and storage, the low-emission or emission-free coal-fired power plant may be much more cost-effective than many alternative energy generation methods. However, a pre- requisite is the existence of adequate storage possibilities. Figures 12.12 and 12.13 show the complete range of estimates of the specific costs for avoiding CO2 in € per t CO2 for nuclear power, fossil energies (coal, oil, gas) and renewable energies (water, wind, sun and biomass).

1) as stated for the German power generation; prices for 2004; related to old lignite power plants (fuel price risk for imported energies considered; subventions for renewable energies not considered) 2) new power plants

Fig. 12.12: Specific costs for avoiding CO2 in €/t CO2 for different energy generation sources (nuclear, lignite, natural gas, hard coal, water, wind, photovoltaic) (source: Engelhard, RWE (http://www0.gsf.de/data2/flugs-Dateien/klima/engelhard- end.pdf))

According to all studies, photovoltaics is the energy generating technology with the highest costs for CO2 avoidance, with the exception of bioethanol and biodiesel, if certain raw materials are used.

170

1) trend in prices of fossil energy sources "medium variant"; related to: Mix of new fossil condensation power plants, corresponding to the reference scenario; 2) Due to the high non-CO2 emissions of bio fuels, e.g. nitrous oxide, only a total consideration of greenhouse gases makes sense; therefore, some indications in € / t per saved CO2 equivalent, some ranges due to differently used raw material. Sources: DLR / IFEU / WI (2004): "Ökologisch optimierter Ausbau der Nutzung erneuerbarer Energien in Deutschland, Ecologi- cally optimised extension of the use of renewable energies in Germany“, study commissioned by BMU; IFEU (2004): "CO2 neutrale Wege zukünftiger Mobilität durch Biokraftstoffe. Eine Bestandsaufnahme, CO2 neutral ways of future mobility. An inventory“, study commissioned by Forschungsvereinigung Verbrennungskraftmaschinen (Union for research of combustion engines; TU Munich (2004): "Costs for avoiding CO2 in power plants, with renewable energies and, depending of the demand, energy efficiency measures“, study commissioned by BMWi Fig. 12.13: CO2 avoidance costs of renewable energy technologies (€/t CO2) (BMU Statusbericht 2006) 171

13 Resumée The vast majority of climate scientists agree on the anthropogenic contribution to the climate change of the past decades. Despite a large uncertainty range in their results, all climate model calculations with increasing anthropogenic emissions show for the future decades that further climate changes will occur. Inevitably there remains considerable uncertainty about regional climate change and the precise nature and magnitude of the environmental health and other impacts. Nonetheless the magnitudes and ranges of the uncertainties do not argue against the need for a worldwide effort to reduce future emissions.

The climate changes to be expected are an increasing problem in the long term, which have to be taken seriously and can only be solved on a global basis. Meeting the Kyoto Protocol targets is a first initial step, but, as calculations have shown, this will practically not lead to any reduction of the expected climate changes (BMBF 2003). In addition to that, with a 15.3 % reduction in 2004, the 35 industrialised countries participating in the Kyoto Protocol, have more than met their obligations of reducing greenhouse gases by an average 5 % by 2008/2012. However, emissions have slightly increased again by 2.9 % since 2000. The EU- 25 achieved a reduction of around 5.6 % in 2005 (8 % promised). Today, the high increase rates in the greenhouse gases are mainly to be found in the quickly developing countries in Asia. In the past 15 years, China has doubled its carbon dioxide emissions, and within a few years, the developing and threshold countries will have surpassed the industrialised countries. Without including these countries, it will not be possible to achieve an effective climate protection. Figure 13.1 shows the success in the carbon dioxide reduction in Germany for the period 1990 to 2005. Within this period, the power industry and industry have contributed most to a reduction of CO2 in Germany. (DNK 2006). According to the BMU, the Kyoto target of a -21 % reduction of the greenhouse gases for Germany for 2008/2012 was nearly met at -19.2 % in 2005.

Fig. 13.1: Reduction of the energy-related CO2 emissions in Germany 1990 – 2005, main contribution: power industry and industry (http://www.co2-handel.de/media/docs/Studien/studie_weltenergierat_2006.pdf, DNK 2006) 172

14 Glossary Absorption of Radiation: Absorption of radiation energy by a solid body, a liquid or a gas. In this process, the energy is absorbed and converted into another form of energy, mainly heat. Absorption bands: Special wave length range of the electromagnetic spectrum, which prominently absorbs radiation energy due to specific properties of gases contained in the atmosphere. Due to the varying molecular structure of different chemical substances, only a section of the spectrum specific to each compound is absorbed, and not the entire spectrum of the radiation (absorption band). Aerobic: Living in the presence of oxygen, with influx of air (in contrast to: anaerobic). Aerosol: Solid or liquid particles in the air - except for water and ice particles - of a size of 0.01 and 10 µm, which remain in the atmosphere for at least several hours. They directly influence the climate by reflection and absorption, and indirectly as condensation nuclei for the formation of clouds or by changing the optical properties and lifetime of clouds. Albedo: Reflective capacity; relation of reflected to incoming solar radiation for a certain surface (e.g. sea surface and plant-covered surface (low albedo) or snow (high albedo)). An increase in albedo counteracts the greenhouse effect. Anaerobic: Living under exclusion of air (in contrast to: aerobic). Annex I Countries: 36 industrialised and transforming countries (economies in transition) listed in Annex I of the UN Framework Convention on Climate Change (UNFCCC). Non An- nex I Countries are the developing and threshold countries. Annex B Countries: 39 industrialised countries and transforming countries (economies in transition) listed in Annex B of the Kyoto Protocol, which have agreed to a legally binding emission reduction (without USA and Australia). Anthropogenic: Resulting from or produced by human beings. Archimedes´ Principle: The buoyancy of a body is equal to the weight force of the fluid dis- placed by the body. Consequently, melting ice does not raise the sea level. Atmosphere: The gaseous envelope surrounding the Earth. Atmospheric Radiation Window: A section of infrared radiation, in which the water vapour in the atmosphere absorbs only little radiation and through which the long-wave radiation emitted by the earth's surface is released almost freely into space. Many greenhouse gases absorb more infrared radiation with the consequence that the concentration increase of greenhouse gases leads to an additional warming of the atmosphere. Biomass: The total mass of living organisms on a certain surface or volume. Biomass is composed of plant mass (phyto mass) and animal mass (zoological mass). The mass of dead and withered parts of plants is often additionally established and specified as "dead biomass". Biosphere: Part of the terrestrial system comprising all living and dead organisms in the atmosphere, on land or at sea.

Carbon Dioxide (CO2): Naturally occurring gas, also a by-product of burning fossil fuels, such as oil, gas and coal, and of biomass, as well as land-use changes and other industrial processes. It is the principal anthropogenic greenhouse gas that affects the Earth’s radiative balance. Plants convert CO2 from the atmosphere in carbohydrates by using of water and solar energy. Its concentration in the atmosphere amounts to 381 ppm. Carbon Dioxide Fertilisation: The enhancement of the growth of plants as a result of increased atmospheric CO concentration. The intensity of the fertilising effect depends on the 2 plant species and its photosynthesis mechanism. Thus, C3 plants (trees, cereal, potatoes, 173 vegetable) react more strongly to CO2 than C4 plants (tropical plants, e.g. grasses, sweetcorn, sugar cane and panic). Carbon Cycle: Cycle of carbon in its different chemical compositions between atmosphere, biosphere, hydrosphere and geosphere. Chlorofluorocarbons (CFC, HCFC): Industrially produced organic carbon compounds containing fluorine and chlorine. Difference is made between completely or partly halogenated CFCs. Completely halogenated CFC exclusively contain carbon and halogens (F, Cl, Br) and have extremely high ozone depleting potentials. Partly halogenated CFCs (HCFC) additionally contain hydrogen atoms making them chemically less stable. Partly halogenated CFCs like H-CFC 22 are used as substitution substances for completely halogenated CFCs. How- ever, partly halogenated CFCs are greenhouse-relevant gases and contribute to the depletion of the ozone layer, although to a limited extent. These substances and their use were prohibited or strongly limited by the Montreal Protocol and additional follow-up agreements. Climate: Climate is in a narrow sense usually defined as the “average weather”, or more rig- orously, as the statistical description in terms of the mean and variability of relevant quantities over a period of time ranging from months to thousands or millions of years. These quantities are most often surface variables such as temperature, precipitation, and wind. Climate in a wider sense is the state, including a statistical description, of the climate system. The classical period of time is 30 years, as defined by the World Meteorological Organization (WMO). Climate Change: Climate change refers to a change in the state of the climate that can be identified (e.g. using statistical tests) by changes in the mean and/or the variability of its properties, and that persists for an extended period, typically decades or longer. Climate change may be due to natural internal processes or external forcings, or to persistent anthropogenic changes in the composition of the atmosphere or in land use. Climate Model: Numerical description of the climate with a mathematical-physical computer model based on the physical, chemical and biological properties of its components, its interactions and feedback processes. Climate Parameters: Internal climate parameters are all those physical variables, such as radiation, temperature and precipitation, which directly characterise the climate. External climate parameters are those influencing factors which although affecting the climate system, do not interact with the same (e.g. solar insolation, volcanoes, anthropogenic emissions of greenhouse gases). Climate Projection: Distinction is made between climate projections and climate prognoses in order to emphasise the dependence of climate projections on the employed emission/concentration and radiative forcing scenarios, which are based on assumptions about e.g. future social and technological developments, that may only potentially become reality, which is why it involves a great degree of uncertainty (see also projection). Climate Sensitivity: Such temperature rise originating from the doubling of greenhouse gas emissions, as compared to the pre-industrial value. The equilibrium climate sensitivity refers to changes of the global average surface temperature following the restoration of the equilibrium as a consequence of the doubling of atmospheric carbon dioxide emissions (compared to the pre-industrial value). Its calculation requires very long simulations with the coupled general circulation models. The average value is reported to be 1.5 – 4.5 °C. Climate System: The climate system is a very complex system consisting of five principle components: atmosphere, hydrosphere, cryosphere, geosphere and biosphere, and their interactions. With the time, the climate system changes due to its own inner dynamics and due to external forces like volcanic eruptions, solar fluctuations and anthropogenically induced influences, such as changes of the composition of the atmosphere or the use of land. Climate Scenarios: In contrast to the weather forecast, climate scenarios do not represent a prognosis, but rather an assessment of the climate in future decades or centuries, based on various assumptions. 174 Climate Variability: Fluctuations of the average state and other statistics of climate (such as standard deviations, occurrence of extreme phenomena etc.) on all space and time scales, which extend beyond individual weather events. Reasons may be natural internal processes of the climate system, or they may originate from natural or anthropogenic external influences. Climate Variations: Short-term changes of climate. CLIVAR: Engl. Abbreviation for Climate Variability & Predictability, an international programme for the research of climate variability and predictability on time scales of months to decades, and of the anthropogenic influence on climate. CLIVAR was started as one of the most important components of the World Climate Research Programme in 1995 and has duration of 15 years.

CO2 Equivalent: Greenhouse effectiveness of a gas in relation to that of CO2 (= 1).

CO2 Fertilising Effect: Enhancement of plant growth due to a higher CO2 concentration in the atmosphere. The fertilising effect varies depending of the respective plant. - CO2 Storage in the Sea: CO2 is stored in water in the form of HCO 3. The maximum amount is defined by the solubility product, which is the product of the concentration of anions and cations in a saturated electrolytic solution. Furthermore, the amount of dissolved HCO3 depends on the ion concentration in the solvent (sea water). Convection: Vertical motion driven by buoyancy forces arising from static instability, usually caused by near surface cooling or salting in the case of the ocean and near surface warming in the case of the atmosphere. Coral Bleaching: Reef-forming corals are to be found in shallow seas. They do not exist in a greater depth than can still be reached by light rays, because the algae living symbiotically in their tissue need the light for photosynthesis, and the corals are unable to exist without algae. Extraordinarily high water temperatures (>29°C) for a longer period of time lead to toxic processes in the corals and to their bleaching. El Niño events, global warming and excess UV radiation due to ozone depletion are discussed as being the reasons for coral bleaching. Cosmic Radiation: Cosmic radiation describes electric particles hitting the earth from outer space. Around 98 % of the cosmic radiation consists of atomic nuclei and 2 % of electrons. Cosmic radiation consists of galactic (GCR) and solar radiation (SCR). The solar cosmic radiation (solar wind) is mainly generated in solar eruptions. Particles with reduced energy often originate from our sun and are ejected in eruptions towards the earth. This component of the cosmic radiation may be identified by its fluctuations depending on the radiation activity of the sun. The galactic cosmic radiation consists of high-energy particles, mainly protons. The principle source for the cosmic radiation is presumably supernovae. Cosmogenic Isotopes: In the atmosphere, cosmic radiation generates radioactive Be-10 isotopes by the decay of nitrogen molecules (half-life: 1.51 million years) and C-14 (half-life 5370 years). They are deposited in ice cores or tree rings and may be used for determining age and solar activity. Cryosphere: Part of the climate system consisting of snow and ice. Dengue Fever: Infectious disease of the tropical and subtropical regions transmitted by mosquitoes of the species aëdes aegypti and communicated by man. The Dengue virus is the pathogen; after an incubation period of 5 to 8 days, symptoms are particularly fever, ar- thritic and muscle pains, swelling of lymphatic nodes and skin rashers. Around 10 million people are infected annually. A vaccine is being developed. Long-lasting rainfalls may favour the development of mosquitoes and thus Dengue fever. Insofar, El Niño events with their regionally enhanced precipitation aggravate its spread. Denitrification: Microbial decomposition of nitrogen compounds, i.e. reduction of nitrate - (NO 3) to atmospheric nitrogen (N2) or dinitrogen oxide (N2O). Deposition: Sedimentation of air-borne substances on surfaces. 175 Easterly Waves: Easterly Waves are atmospheric wave disturbances which, being low tropical disturbances, travel east-west from the African continent towards the Atlantic. Under certain conditions, easterly waves can convert into birthplaces for tropical cyclones. Economies in Transition, EIT: Poland, Czech Republic, Hungary, Slovakian Republic, Russian Federation, Ukraine, Bulgaria, Estonia, Croatia, Latvia, Lithuania, Romania, Slove- nia, Belorussia. El Niño-Southern Oscillation (ENSO): A coupled fluctuation in the atmosphere and the equatorial Pacific Ocean, with preferred times scales of 2 to about 7 years. During an El Niño Event the surface water off the Peruvian coastline and along the equatorial Pacific is considerably warmer than in the annual average. Emission Scenario: A plausible description of future trends in the emission of substances possibly influencing radiation (e.g. greenhouse gases, aerosols) based on a coherent and in itself consistent sequence of assumptions about the driving forces (like demographic and socio-economic developments or technological change) and their key relations. Energy-Attributable Climate-Relevant Trace Gases: Trace gases emitted during the pro- vision, conversion and use of energy, which directly and indirectly lead to climate change: carbon dioxide (CO2), methane (CH4), nitrous oxide (laughing gas, N2O), trace gases, contributing to the formation of ozone (O3) in the troposphere or producing changes in the air chemistry, i.e. mainly nitrogen oxides (NOx), carbon monoxide (CO), carbohydrates (CxHy) and sulphur dioxide (SO2). Energy balance: The difference between the total incoming and total outgoing energy of the climate system. If this balance is positive there is global warming; if it is negative there is global cooling. Averaged over the globe and over longer time periods, this balance must be zero. Earth's Orbit: The orbit of the earth is determined by the eccentricity of the terrestrial orbit, the precession of the point of the terrestrial orbit which is closest to the sun, and the inclination of the axis of the earth. These three parameters have periods of around 20,000, 40,000 and 100,000 years. Equivalent CO2 (carbon dioxide): The concentration of carbon dioxide that would cause the same amount of radiative forcing as a given mixture of carbon dioxide and other greenhouse gases. Eutrophication: Excess fertilisation, i.e. excessive supply of nutrients containing nitrogen and phosphate. Eccentricity: The distance of the focal points from the centre of the elliptical earth orbit. F-Gases: The Kyoto Protocol lists the climate-relevant fluorochlorocarbons (HFC), the per- fluorinated chlorocarbons (PFC and FC) and SF6. HFC and PFC are partly used as a substitution for the ozone-depleting CFCs. Feedback: A feedback occurs if one process triggers changes in another process, which itself in turn influences the original process. A positive feedback enhances the original process, a negative one reduces it. Flux Adjustment: In order to avoid the problem of general coupled atmosphere/ocean models shifting towards an unrealistic climate situation, heat and humidity flows between ocean and atmosphere (and sometime the pressure produced by wind on the sea surface) may be adjusted prior to inserting these flows into the model ocean and the model atmosphere. Most models used in the AR4 Report (AR4 AOGCMs) do not use flux adjustments. Fossil Fuels: Fuels deposited in the earth crust having evolved from plants or animals of past geological times (coal, oil, natural gas). Greenhouse Effect: Greenhouse gases effectively absorb infrared radiation, emitted by the Earth’s surface, by the atmosphere itself due to the same gases, and by clouds. Atmospheric radiation is emitted to all sides, including downward to the Earth’s surface. Thus greenhouse gases trap heat within the surface-troposphere system. This is called the greenhouse effect. Due to the heat-insulating effect of these trace gases the temperature near ground level is 176 approx. 33 °C higher than the radiation temperature of the earth/atmosphere system without these gases (natural greenhouse effect). As to increasing anthropogenic trace gases, the so- called anthropogenic greenhouse effect, will enhance and temperatures will rise. Greenhouse Gases: Greenhouse gases are those gaseous constituents of the atmosphere, both natural and anthropogenic, that absorb and emit radiation at specific wavelengths within the spectrum of infrared radiation emitted by the Earth’s surface, the atmosphere itself, and by clouds. This property causes the greenhouse effect. Water vapour (H O), carbon dioxide 2 (CO ), nitrous oxide (N O), methane (CH ) and ozone (O ) are the primary greenhouse 2 2 4 3 gases in the Earth’s atmosphere. Moreover there are a number of entirely human-made greenhouse gases in the atmosphere, such as the halocarbons and other chlorine and bromine containing substances, dealt with under the Montreal Protocol. Beside CO , N O and 2 2 CH , the Kyoto Protocol deals with the greenhouse gases sulphur hexafluoride (SF ), hydro- 4 6 fluorocarbons (HFCs) and perfluorocarbons (PFCs). Global Warming Potential (GWP): An index, based upon radiative properties of well mixed greenhouse gases, measuring the radiative forcing of a unit mass of a given well mixed greenhouse gas in today’s atmosphere integrated over a chosen time horizon, relative to that of carbon dioxide (GWP = 1). The GWP represents the combined effect of the differing times these gases remain in the atmosphere and their relative effectiveness in absorbing outgoing infrared radiation. . The Kyoto Protocol is based on GWPs from pulse emissions over a 100 year time frame. Methane GWP 23 (21), SF6 GWP 22,200 (23,900), N2O GWP 296 (310), FC GWP 6,000 – 9,000. Values taken from the 3rd Assessment Report (IPCC 2001), in brackets from the 2nd Assessment Report of IPCC 1995 (for calculations according to Kyoto Proto- col). Halogenated Hydrocarbons (HHC): Compound formed when the hydrogen in a hydrocar- bon molecule, such as methane, is replaced by any of the halogens (fluorine, chlorine, bromine and iodine. The best known group of halogenated hydrocarbons are the chlorofluorocarbons (CFCs). Halocarbons: (general term) carbonaceous compounds containing halogens (Cl, Br, F, J). Completely halogenated halocarbons exclusively contain carbon and halogen atoms, whereas partly halogenated halocarbons additionally contain hydrogen atoms. Halocarbons containing chlorine, bromine and iodine cause the ozone depletion in the stratosphere. Halo- carbons are also greenhouse gases (see chlorofluorocarbons). Halons: Chemical denomination for modified hydrocarbons, which instead of hydrogen atoms contain one or several halogen atoms like fluorine, chlorine or bromine, but at least one bromine atom. Halons contribute to the stratospheric ozone depletion and are mainly employed in fire extinguishing installations. Pursuant to the Montreal Protocol, their use is no longer admissible in most countries. Hydrosphere: The waters of the earth. Ice Cores: An important method for the reconstruction of climate changes. Ice cores are taken from central areas in the polar ice shields and ice caps (glacier type). Ice cores are used to analyse the composition of the air sealed in the small air pores in the ice, which is to reveal the composition of the atmosphere at the time of snow accumulation or formation of ice. The ratio of oxygen isotopes (18O/16O) gives information about the paleo temperature, and the acidity index (measured by means of electrical conductivity) of the gases from volcanic eruptions contained in the ice. The "dust veil index" (DVI) bears evidence of dust particles also contained in the ice, they proceed from volcanic eruptions, too. Infrared Radiation (IR): Infrared radiation is an electromagnetic radiation with a wavelength of around 0.7 to 1,000 micrometers, which lies above visible and below microwave radiation. The majority of energy emitted by the earth and its atmosphere lies within the infrared range. Infrared radiation is almost completely generated in intra molecular processes. The three- atomic gases like water vapour, carbon dioxide and ozone absorb infrared radiation and play an important role in the propagation of infrared radiation in the atmosphere. 177 Inclination of the Axis of the Earth: Inclination of the rotational axis of the earth towards the ecliptic plane around the sun. Innertropical Convergence Zone (ITC): The near-equator zone, in which the trade winds from the North and South meet (according to the season around 20° north or south of the equator). Thereby, they are forced to rise, which leads to clouds formation and precipitation. IPCC: Intergovernmental Panel on Climate Change, intergovernmental expert panel for climate issues under the auspices of the United Nations, which was established in 1988. Jet Stream: Belt-formed air current with extraordinarily high wind speeds (approx. 600 km/h maximum) in the upper troposphere or lower stratosphere caused by extreme horizontal temperature differences and Coriolis force. Length: some 1,000 km, width: some 100 km, vertical thickness: some km. Long-Wave Spectral Range: Range of electromagnetic radiation between 4 and 100 µm (infrared radiation). Within this range, the earth emits heat radiation into space. Lifetime: General term for different time scales, which describe the velocity of processes that influence the trace gas concentration. A difference is made between turnover time and adaptation time. Turnover time is the ratio between the mass of a storage (e.g. of a gas in the atmosphere) and the total reduction rate of the storage. The adaptation time is the time scale, which is characteristic for the reduction of an amount suddenly introduced in this storage. Frequently, adaptation time is referred to as lifetime. For CO2, this specification is particularly difficult, because the gas retained in the biosphere is released again. By approximation, a value of 100 years is frequently reported. Lithosphere: The upper layer of the solid Earth, both continental and oceanic, which comprises all crustal rocks and the cold, mainly elastic, part of the uppermost mantle. Kyoto Protocol: In 1997, it was adopted by the third COP of the UN Framework Convention of Climate Change (UNFCCC) in Kyoto, Japan, and it entered into force in February 2005. The industrial countries (Annex B Countries) except for USA and Australia, and the transforming countries have agreed therein to reduce greenhouse gas emissions in CO2 equivalents (CO2, CH4, N2O, H-CFC, FC, SF6) by 5 % between 2008 and 2012, compared to 1990, and, with respect to the last three gases, compared to 1995 (http://unfcc.int/resource/docs/konvkp/kpeng.pdf). Meridional Circulation: In this circulation form, the spacious currents in the atmosphere are arranged meridionally, i.e. along the longitudes. This current system allows for a direct air exchange between polar and subtropical regions. Meridional Overturning Circulation (MOC): Meridional (north-south) overturning circulation in the ocean quantified by zonal (east-west) sums of mass transports in depth or density layers. In the North Atlantic, away from the subpolar regions, the MOC (which is in principle an observable quantity) is often identified with the THC (which is a conceptual interpretation). MOC can also include shallower, wind-driven overturning cells such as occur in the upper ocean in the tropics and subtropics, in which warm (light) waters moving polewards are transformed to slightly denser waters and subducted equatorwards at deeper levels. Methane (CH4): Methane is a chemical compound with the molecular formula CH4. Methane is a relatively potent greenhouse gas with a global warming potential of 23. Mole Fraction: Mole fraction, or mixing ratio, is the ratio of the number of moles of a constituent in a given volume to the total number of moles of all constituents in that volume. It is usually reported for dry air. Typical values for long-lived greenhouse gases are in the order of μmol/mol (parts per million: ppm), nmol/mol (parts per billion: ppb), and fmol/mol (parts per trillion: ppt). Mole fraction differs from volume mixing ratio, often expressed in ppmv etc., by the corrections for non-ideality of gases. This correction is significant relative to measurement precision for many greenhouse gases. Monsoon: Monsoons are tropical winds, which change their direction according to the season. They superimpose the meridional tropical circulation and depend on the shifts of the inner tropical convergence zone (ITC). The winter monsoon above India corresponds to the 178 tropical north-east trade wind which transports dry, cool continental air above the Indian sub- continent to the ITC. In summer, ITC shifts north, travelling over India towards the Himalaya. The oceanic origin of these air masses leads to the vital monsoon rains above India and Southeast Asia. Montreal Protocol: The Montreal Protocol on Substances that Deplete the Ozone Layer was adopted in Montreal in 1987, and subsequently adjusted and amended in London (1990), Copenhagen (1992), Vienna (1995), Montreal (1997) and Beijing (1999). It controls the consumption and production of chlorine- and bromine-containing chemicals that destroy stratospheric ozone, such as CFCs, methyl chloroform, carbon tetrachloride, and many others. North Atlantic Oscillation (NAO): The North Atlantic Oscillation consists of opposing variations of barometric pressure near Iceland and near the Azores. It therefore corresponds to fluctuations in the strength of the main westerly winds across the Atlantic into Europe, and thus in the embedded cyclones with their associated frontal systems. - Nitrification: Microbial conversion of nitrogen during which first nitrite ions (NO 2) and then - + nitrate ions (NO 3) are formed in a two-step process from ammonium ions (NH 4).

Nitrogen Oxides (NOx): The sum of nitric oxide (NO) and nitrogen dioxide (NO2).

Nitrous oxide (N2O): also known as dinitrogen oxide or dinitrogen monoxide (Laughing gas) is a chemical compound with chemical formula N2O. Nitrous oxide acts in the atmosphere as a powerful greenhouse gas. Optical Thickness (atmosphere): A measure for the weakening of the electromagnetic radiation during passage of gas layers or the atmosphere. It is the product of the spectral ex- tinction coefficient and the wavelength of the gas layers passed by radiation. Orography: Description of surface forms, land masses, knowledge about mountains. Ozone (Greek for the smelling): Ozone, the triatomic form of oxygen (O ), is a gaseous at- 3 mospheric constituent. In the troposphere it is created both naturally and by photochemical reactions involving gases resulting from human activities (“smog”). Tropospheric ozone acts as a greenhouse gas. In the stratosphere it is created by the interaction between solar ultra- violet radiation and molecular oxygen (O ). Stratospheric ozone plays a dominant role in the 2 stratospheric radiative balance. Its concentration is highest in the ozone layer. Ozone Hole: In 1985 it was discovered that since 1977, there have been drastic reductions of the ozone concentrations above Antarctica in the months of September and October. This observed reduction of the ozone layer above Antarctica and above the North Polar regions is called ozone hole. Meanwhile, it was stated that the annually recurring ozone hole is also caused by industrially produced chlorofluorocarbons. The ozone layer protecting us from UV radiation, is expected to recover within the next decades due to the prohibition of CFCs. Ozone Layer: The stratosphere contains a layer in which the concentration of ozone is greatest, the so-called ozone layer. The layer extends from about 12 to 40 km above the Earth’s surface. This layer is being depleted by human emissions of chlorine and bromine compounds. Every year, during the Southern Hemisphere spring, a very strong depletion of the ozone layer takes place over the Antarctic region, caused by human-made chlorine and bromine compounds in combination with the specific meteorological conditions of that region. This phenomenon is called the ozone hole. Paleoclimate Data: Climate data (e.g. temperature) taken from the earth history. This data may proceed from ice cores, sediments on the seabed, tree ring analyses and pollen analyses. Parametrization: In climate models, this term refers to the technique of representing processes that cannot be explicitly resolved at the spatial or temporal resolution of the model (sub-grid scale processes), by relationships between model-resolved larger scale flow and the area or time averaged effect of such sub-grid scale processes. 179 Pedosphere: Soil, limiting area of the terrestrial surface where rock, water, air and living species interfuse and the soil-forming processes take place. Photochemically: Chemical reactions which take place under the effect of UV radiation. Photodissociation: Dissociation under the influence of light (UV radiation). Photolysis: Dissociation of molecules by absorption of light (electromagnetic radiation). Photosynthesis (Assimilation): The build-up of carbohydrates from carbon dioxide and water by green plants with sunlight.

Formula: CO2 + H2O + chlorophyll + light > (CH2O) x + O2 Plankton: Symbiosis of organisms floating in water with missing or nearly missing own movements. Zoologic plankton: planktic animals, phytoplankton: planktic plants. Nutrition for fish. ppm (parts per million) or ppb (parts per billion, 1 billion = 1,000 million): is the ratio of the number of greenhouse gas molecules to the total number of molecules of dry air. Polar Vortex: A wind surrounding the Poles, which is particularly strong in Antarctica. The Antarctic Polar vortex may achieve a high stability and very low temperatures Precession: Circular rotation of the earth's axis around its body axis caused by the gravita- tion of sun and moon. One rotational movement takes around 20.000 years. Precursors: Atmospheric compounds which themselves are not →greenhouse gases or aerosols, but which have an effect on greenhouse gas or aerosol concentrations by taking part in physical or chemical processes regulating their production or destruction rates. Projection: In climatology, results of model calculations for future climates are not called prognosis but projection, as they are based on varying emission scenarios and the likelihood of their occurrence has not yet been assessed (see also climate projections). Prominences: Gaseous clouds of electrically charged particles which may be observed along the solar edge. Their extent ranges from 50,000 km to 1 million km, the latter to be very rare. Prominences are connected to sunspots. Coronal mass ejections (CME) are gi- gantic explosions caused by suddenly bursting magnetic field lines. During this event, billions of tons of material are ejected into space with up to 2000 km/s. Proxydata: Approximation data of hydrologic and meteorological conditions in historical and prehistorical times. It is found in local data sources, the proxies, by application of physical and biophysical methods. Such indicators of the paleo climate are ice cores, pollen, warves, tree rings, stalagmites, properties of corals, indicators for glacier levels, historical references, crop yield figures, phenologic phases, indications about icings or floods, decay properties of isotopes. Radiative forcing: Radiative forcing is the change in the net vertical irradiance (expressed -2 in Watts per square meter: Wm ) at the tropopause due to an internal change or a change in external forcing of the climate system, such as, for example, a change in the concentration of carbon dioxide or the output of the Sun. Radiometer: A passive instrument, which measure the amount of electromagnetic radiation, generally in the microwave and infrared range. Weather satellites carry radiometers to measure the radiation of snow, ice, clouds, water bodies, the terrestrial surface and the sun. They determine the amount of liquid water and water vapour in the atmosphere. Radiosonde: An instrument carried by a balloon, which measures meteorological parameters in an altitude of up to approx. 30 km. Temperature, air pressure and humidity are measured and transmitted to the earth. Generally, radiosondes are ascended twice a day everywhere worldwide (00.00 and 12.00 UTC). Short-Wave Spectral Range: Range of electromagnetic radiation between 0.2 and 4 µm (solar radiation). 180 Sea Surface Temperature (SST): Simplified: The temperature measured via the radiation emitted by the sea surface. The temperature ranges from around -2 °C in the Polar regions to 32 °C in the Tropical regions. Since ocean currents have characteristic temperatures, SST is the preferred data type for observing the sea circulation. The sea surface temperature has a significant influence of the exchange of heat, humidity, impulse and gases between atmosphere and sea. Satellite sensors are well-suited for measuring SST. Sinks: An ecosystem (sea, forests), which withdraws carbon from the atmosphere is a sink (for example, a tree withdraws carbon from the atmosphere during its growth). The binding of carbon in sinks can be credited up to certain limits to the emission reduction targets set under the Kyoto Protocol. Slash-and-Burn: Clearing of forest surface by using fire to prepare it for agricultural use. Through the conversion of carbon-rich ecosystems, such as the tropical rainforests, into surfaces with considerably reduced carbon contents (e.g. agriculturally used surfaces), significant amounts of CO2 are released and emitted into atmosphere. Soil Erosion: The removal of soil by water, ice, wind and gravity. Solar Activity: The Sun exhibits periods of high activity observed in numbers of sunspots, as well as radiative output, magnetic activity, and emission of high energy particles. These variations take place on a range of time-scales from millions of years to minutes. Solar Cycle: Period of 11 years in average, during which the amount of sunspots in the solar surface passes through a cycle. Solar Constant: Specifies solar radiation, which arrives vertically on a surface outside the atmosphere (average value around 1,367 W/m2). In space it is nearly constant, on earth it varies according to day time or season (±3.5 %), latitude and weather. Solar radiation: Electromagnetic radiation emitted by the Sun. It is also referred to as short- wave radiation. Solar radiation has a distinctive range of wavelengths (spectrum) determined by the temperature of the Sun, peaking in visible wavelengths. Source: Any process, activity or mechanism which releases a greenhouse gas, an aerosol or a precursor of a greenhouse gas or aerosol into the atmosphere Southern Oscillation: Air pressure oscillation (vibration), which is reflected in the mass shift between the Indonesian equatorial low pressure cell and the Southern Pacific high pressure cell (east-west air pressure vibration). Southern Hemisphere Annular Mode (SAM) (Antarctic Oscillation, AAO): air pressure fluctuations (variability mode) on the Southern hemisphere with the polar vortex as centre of action with consequences for the soil temperature. Stratosphere: The highly stratified region of the atmosphere above the troposphere extending from about 10 km (ranging from 9 km in high latitudes to 16 km in the tropics on average) to about 50 km altitude. Sulphuric Acid Aerosol: It is formed by atmospheric oxidation of SO2 and has a cooling effect. Main component of the stratospheric aerosol layer (in altitudes between 15 and 25 km). Sunspots: Small dark areas on the sun with a lower surface temperature compared to the solar surface. They emerge because the strong magnetic field passing through the solar surface suppresses the energy transport by gas flows. The number of sunspots is higher during periods of high solar activity, and varies in particular with the solar cycle.

Solar Wind: Solar wind is the total amount of all particles emitted by the sun (solar cosmic radiation). It mainly consists of electrically charged particles, such as helium nuclei, electrons and protons. The solar wind influences the magnetic field of the sun and the earth, as well as the galactic cosmic radiation. A strong solar wind may penetrate the terrestrial atmosphere and cause aurora borealis. Sun-Synchronous: The orbits of the weather satellites are additionally sun-synchronous. All parts of the earth are passed under the same solar illumination, i.e. on the same local time. Thus, the images can be directly compared to each other. 181 Radiance: Radiance is the radiation flux per penetrated area unit and solid angle in a given direction. Radiative Forcing: The radiative forcing indicates the change in the vertical net radiation (in W/m2) in the tropopause, which is caused by an internal change or changes in the external forcing of the climate system, e.g. the change in CO2 concentration or solar radiation. Scenario: Evaluation of a possible situation under the assumption of certain conditions. The results are independent of boundary conditions of the scenarios and therefore differ from the prognosis. Solar Radiation Flux: (Short-wave) radiation emitted by the sun (see solar constant). Stratosphere: Multilayered zone of the atmosphere above the troposphere between 10 and 50 km of altitude. Suess Effect (according to Hans E. Suess (1909–1993): Fossil fuels like crude oil and coal do not contain detectable C-14 because they are significantly older than approx. 10 half- lives (around 60,000 years). During their combustion, only the (non radioactive) isotopes C- 12 and C-13 of the fossil fuels are emitted and dilute the amount of radioactive C-14 in the atmosphere. Thermohaline Circulation: Large-scale circulation of the oceans triggered by differences in temperature and salinity of the water. In the North Atlantic, warm surface water flows north and cold deep water flows south, resulting in a heat transport directed towards the Pole (see also MOC). Trace Gases: Gases, which are present in the atmosphere only in small concentrations, e.g.CO2, CH4, N2O, CH4, CFC. Trade Winds: Winds existing on both sides of the equator up to approx. 25° N and S, which flow from high pressures at the horse latitudes towards the equatorial trough of low pressure for pressure compensation. In the trade winds zones, air drops. It is not until the flowing together of the trade winds in the equatorial trough of low pressure, that the air masses are forced to rise and start to rain. Tropopause: Boundary layer between troposphere and stratosphere. Troposphere: The lowest part of the atmosphere from the surface to about 10 km in altitude in mid-latitudes (ranging from 9 km in high latitudes to 16 km in the tropics on average) where clouds and weather phenomena occur. In the troposphere temperatures generally decrease with height. Ultra Violet Radiation (UV): Electromagnetic energy with higher frequencies or shorter wavelengths (below 400 nm) than visible light; UV radiation groups into three classes: UV-A (320 - 400 nm), UV-B (280 - 320 nm) and UV-C (40 - 280 nm). Uncertainty: An expression of the degree to which a value (e.g. the future state of the climate system) is unknown. Uncertainty can result from lack of information or from disagree- ment about what is known or even knowable. It may have many types of sources, from quan- tifiable errors in the data to ambiguously defined concepts or terminology, or uncertain projections of human behaviour. Uncertainty can therefore be represented by quantitative measures (e.g. a range of values calculated by various models) or by qualitative statements (e.g., reflecting the judgement of a team of experts). United Nations Framework Convention on Climate Change: (UNFCCC) The framework convention (www.unfccc.int/resource/docs/convoke/conger.pdf) was adopted at the Earth Summit for Environment and Development in Rio de Janeiro in 1992, and since that it has been ratified by 186 states. It entered into force in 1994. Its ultimate objective is the “stabilisation of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system”. The convention sets the framework for climate protection negotiations, respectively taking place as Conference of the Parties (COP) of the convention. The secretariat of the Framework Convention on Climate Change, the UNFCC secretariat, is based in Bonn. 182 Upwelling: Describes the rising of deeper, generally colder and more dense sea water to the surface, this process occurs mainly in certain upwelling sites. In areas with upwelling, considerable amounts of carbon dioxide are emitted into the atmosphere. This is of specific importance for the equatorial Pacific, where 1-2 Gt C/a may be emitted. At the same time, upwelling sites are characterised by an increased primary production (formation of plankton). Volatile Organic Compounds (VOC, NMVOC): All organic compounds except for methane, which are able to produce photochemical oxidants like ozone in a reaction with nitrogen oxides and in the presence of sunlight. Walker Circulation: Denomination for zonal wind circulation cells above the equatorial Pa- cific. Water Vapour Window: Denomination for areas of the electromagnetic spectrum (3-5 µm, 8-11 µm, partly up to 20 µm), where the greenhouse gas "water vapour" only has a small absorption effect and thus facilitates the terrestrial radiation into space (if the atmosphere is clear).

Amongst others, the following links were used for the glossary: IPCC Glossary for Climate Change 2001, 2007 (www.greenfacts.org/de/klima-wandel/toolboxes/glossary.htm), ENSO-Lexikon (www.enso.info/enso-lexikon/lexikon.html), Fernerkundungslexikon (Remote Sensing Encyclopaedia) (www.fe-lexikoninfo/pages/lexikon- f.htm). 183

15 Abbreviations AO Arctic Oscillation AAO Antarctic Oscillation AOGCM Coupled atmosphere/ocean model ACIA Arctic Climate Impact Assessment (intern. Arctic project with Report in 2004) ACSYS Arctic Climate System Study AMSU Amplified Microwave Sounding Unit AR4 Fourth Assessment Report (IPCC) BMBFT Bundesministerium für Bildung, Forschung und Technologie (Federal Ministry of Education and Research) BMU Bundesministerium für Umwelt, Naturschutz und Reaktorsicherheit (Federal Ministry for the Environment, Nature Conservation and Nuclear Energy)

CCS Carbon Capture and Storage CCSP Climate Change Science Program USA CFC Chlorofluorocarbons

CH4 Methane CLIVAR Climate Variability and Predictability Programme CMC Chemical Coupled Model CMIP Coupled Model Intercomparison Project CO Carbon monoxide

CO2 Carbon dioxide COP Conference of the Parties of UNFCC CTM Chemical transport model DEKLIM Deutsches Klimaforschungsprogramm (German Climate Research Pro- gramme - Programme of the Federal Ministry of Education and Research) DPG Deutsche Physikalische Gesellschaft, German Physical Society DWD Deutscher Wetterdienst, German Meteorological Service EEA European Environment Agency EMIC Earth system model of intermediate complexity ENES European Network for Earth System Modelling ENSO El Niño Southern Oscillation EPICA European Project for Ice Coring in Antarctica (1996-2006) ESM Earth system model CFC Chlorofluorocarbons FRA Forest Resources Association GOME Global Atmosphere Monitoring Experiment GWP Global Warming Potential 184 HBS Hamburger Bildungsserver (Hamburg Education Server) HFC Hydrofluorocarbons, fluorocarbons containing hydrogen HCFC Chlorofluorocarbons containing hydrogen ICSU International Council for Science (internat. umbrella organisation of scientific academies) IEA International Energy Agency IGCC Integrated Gasification Combined Cycle, coal gasification process with gas and steam turbine plant INDOEX Indian Ocean Experiment (field experiment on the feedback sea – atmosphere) IPCC International Panel of Climate Change of the UN IR Infrared ITC Innertropical Convergence Zone LIA Little Ice Age LULUCF Land use, land use change and forestry, IPCC Special Report KLIWA Klimaveränderung und Konsequenzen für die Wasserwirtschaft, Climate Change and Consequences for Economy (Co-operation plan between Baden- Württemberg, Bavaria and DWD, German Meteorological Service) MOC Meridional Ocean Circulation MOP Meeting of the Signatory Parties of the Kyoto Protocol MPI-M Max Planck Institute for Meteorology, Hamburg MSU Microwave Sounding Unit MWP Medieval Warm Period NAO North Atlantic Oscillation NASA National Aeronautics and Space Administration NIR National Inventory Report NOAA National Oceanic and Atmospheric Administration, USA

N2O Dinitrogen oxide, laughing gas

NH3 Ammonia NMVOC Non Methane Volatile Organic Compounds NO Nitric oxide

NO2 Nitrogen dioxide PCMDI Program for Climate Model Diagnosis and Intercomparison PIK Potsdam Institute for Climate Impact Research, Germany PFC Perfluorocarbon ppb parts per billion, one part in 109. ppm parts per million, one part in 106 — 0.0001%. PRUDENCE Prediction of Regional Scenarios and Uncertainties for Defining European Climate Change Risks and Effects (EU research programme) 185 RSS Remote Sensing Systems, Santa Rosa California SAM Southern Annular Mode, Antarctic Oscillation

SF6 Sulphur hexafluoride

SO2 Sulphur dioxide SPM Summary for Policy Makers, IPCC SRES Special Report on Emission Scenarios IPCC TAR Third Assessment Report (IPCC) THC Thermohaline Circulation GHG Greenhouse gases TOC Total amount of carbon TS Technical Summary UAH University of Alabama, Huntsville UBA Umweltbundesamt (Federal Environment Agency, Dessau, Germany) UNEP United Nations Environment Programme UNFCCC United Nations Framework Convention on Climate Change VDEW Verband der Elektrizitätswirtschaft e.V. (Association of the German Power industry) VGB VGB PowerTech e.V. , European technical association for power and heat generation VOC Volatile organic compounds WBGU Wissenschaftlicher Beirat der Bundesregierung (scientific advisory board of the Federal Government, Germany) WCI Water Cycle Initiative of USGCRP (US Global Change Research Program) WDCGG World Data Center for Greenhouse Gases WMO World Meteorological Organisation WCRP World Climate Research Programme ZVEI Zentralverband der Elektroindustrie, central technical association of the electrical industry

1 Mg = 106 g = 1 t, 1 Gg = 109 g = 1000 t, 1 Tg = 1012 g = 1 million t 186

16 Selected Literature

16.1 Books, Brochures Berner, U. und Streif, H.-J .(2004): Der Rückblick – Ein Schlüssel für die Zukunft, 4. Auflage, 259 Seiten, ISBN 3-510-95913-2, Klimafakten, Schweizerbart’sche Verlagsbuchhandlung BMBF (2003): Herausforderung Klimawandel, Broschüre (www.bmbf.de/pub/klimawandel.pdf) Brönnimann, S. (2002): Ozon in der Atmosphäre. Verlag Paul Haupt AG, Bern, 184 S. Cubasch, U. und Kasang, D. (2000): Anthropogener Klimawandel. Klett-Perthes-Verlag, Stuttgart, ISBN 3-623-00856-7, 128 S. Diaz, H., and Markgraf, V. (2000): El Niño and the Southern Oscillation: Multiscale Variability and Global and Regional Impacts. Cambridge University Press, 496 S Düwel-Hösselbart (2002) Ernteglück und Hungersnot, Konrad Theiß Verlag GmbH, Stuttgart, 144 S. Glaser, R. (2001): Klimageschichte Mitteleuropas, Primus-Verlag, Darmstadt, 227 S. Hauser, W. (2002): Klima. Das Experiment mit dem Planeten Erde., Begleitband und Katalog zur Sonderausstellung des Deutschen Museums vom 7.11.2002 bis 15.6.2003, München Hupfer, P., und Kuttler, W. (2005): Witterung und Klima, B.G. Teubner Verlag, Stuttgart, 554 S. Hurrell, J., Kushnir, Y., Ottersen, G., and Visbeck M. (2003): The North Atlantic Oscillation. Climate Significance and Environmental Impact. AGU, Washington DC IPCC (2001): Climate Change 2001: The Scientific Basis, Cambridge University Press UK, S. 944 ff (Third Assessement Report. WG 1) IPCC 2001 (2002): Klimaänderung 2001, Synthesebericht, Herausgeber: Deutsche IPCC Koordinierungsstelle des BMBF und des BMU (http://www.ipcc.ch/pub/nonun/IPCC02_Synthese_D.pdf) Klima (2002): Das Experiment mit dem Klima Erde, Begleitband und Katalog zur Sonderaus- stellung des Deutschen Museums vom 7.11.2002 bis 15.6.2003, München, S. 138-149 Latif, M. (2003): Hitzerekorde und Jahrhundertflut. Herausforderung Klimawandel. Was wir jetzt tun müssen. Heyne Verlag, 160 S. Latif, M. (2004): Klima. Fischer Kompakt. Fischer Verlag, 127 S. Lauer, W., und Bendix, J. (2004): Klimatologie, 2. Auflage, Westermann Schulbuchverlag, Braunschweig Lozán, J. L., Graßl, H., Hupfer, P. (1998): Warnsignal Klima. Wissenschaftliche Fakten. 465 S., Wissenschaftliche Auswertungen + GEO, Hamburg; engl. überarbeitete Ausgabe 2001 Pfister, C. (1999): Wetternachhersage. 500 Jahre Klimavariationen und Naturkatastrophen (1496-1995). Verlag Paul Haupt Promet (2002): Das Klimasystem der Erde, DWD, Heft 3/4, Teil I Promet (2003): Modellierung natürlicher Klimaschwankungen, DWD, Heft 1-4, Teil II Promet (2004): Modellierung der Klimaänderungen durch den Menschen, 1.und 2. Teilheft, DWD, Heft 3 und 4 Teil III Rahmstorf, S., und Schellnhuber H.J. (2006): Der Klimawandel, Verlag C. H. Beck, 144 S. Schellnhuber, Hans Joachim, W. Cramer, N. Nakicenovic, T. Wigley und G. Yohe (Hrsg.) (2006): Avoiding Dangerous Climate Change, Cambridge University Press Schönwiese, C.-D. (2003): Klimatologie, 2. Auflage, Ulmer (UTB), Stuttgart Schuchardt, B., und Schirmer, M. (2005): Klimawandel und Küste: Die Zukunft der Unterwe- serregion. Springer Verlag, Heidelberg, 342 S. Wanner, H., Gyalistras D., Luterbacher, J., Rickli, R., Salvisberg, E., und Schmutz, C. (2000): Klimawandel im Schweizer Alpenraum. vdf Hochschulverlag AG an der ETH, Zürich, 296 S. 187 16.2 Articles (selection of literature, particularly after the IPCC Report 2001) ACIA Bericht (2005): Arctic Climate Impact Assessement (http://www.acia.uaf.edu/pages/scientific.html) Adams, J. B., Mann, M. E., and Ammann, C. M. (2003): Proxy evidence for an El Niño-like response to volcanic forcing, Nature 426, S. 274-278 AFO 2000 (2005): Results of the German Atmospheric Research Programme – AFO 2000 Alley, R. B., et al. (2005): Ice Sheet and Sea-Level Changes, Science 310, S. 456-460 Avoiding Dangerous Climate Change, Scientific Symposium on Stabilisation of Greenhouse Gases, Febr. 1st to 3rd, 2005, Met Office, Exeter, United Kingdom (http://www.defra.gov.uk/environment/climatechange/internat/dangerous-cc.htm) AWI (2006): Rekordluftverschmutzung über der Arktis, Pressemitteilung.AWI, 11.05.2006 Bader, D. (2004): An Appraisal of Coupled Climate Model Simulations, UCRL-TR-202550 (www-pcmdi.llnl.gov/model_appraisal.pdf) Bard, E. (2005): More Notes on Global Warming, Physics Today, May 2005, (www.Physicstoday.org) Barnett, T. P., et al. (2005): Penetration of Human-Induced Warming into the World’s Oceans, Science 309, No. 5732, S. 284-287 Barring, L., and Von Storch, H. (2004): Scandinavian storminess since about 1800, Geophys. Res. Lett., 31, L20202, GL020441 Bartels H., et al. (2006): Klimaentwicklung und Hochwasserschutz, Klimastatusbericht 2005 (DWD), S. 33-43 BASC (2005): Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties, Board on Atmospheric Sciences and Climate (BASC), National Academy of Science, USA Bauer, E., Claussen, M., Brovkin, V. (2003): Assessing climate forcing of the earth system for the past millenium, Geophys. Res. Lett. 30, No. 6, S. 1276 Bellouin, N., et al. (2005): Global estimate of aerosol direct radiative forcing from satellite measurements, Nature 438, S. 1138-1141 Bengtsson, L. (2004): Natürliche und anthropogene Antriebe des Klimasystems und die Fol- gen in Klimamodellrechnungen für Vergangenheit und Zukunft, Promet (DWD) 30, Nr.4, S. 188-201 Bengtsson, L., et al. (2004): The Early Twentieth-Century Warming in the Arctic – A Possible Mechanism, J. Climate 17, S. 4045-4057 Bindschadler, R. (2006): Hitting the Ice Sheets where it hurts, Science 311, No. 5768, S. 1720-1721 Blessing, S., et al. (2005): Daily North-Atlantic Oscillation (NAO) index: Statistics and its stratospheric polar vortex dependence, Meteorologische Zeitschrift 14, No. 6, S. 763-769 Bissolli P. (2001): Vulkanismus und Klima, Klimastatusbericht 2000, DWD Bond, G., et al. (2001): Persistent solar influence on North Atlantic surface circulation during the Holocene, Science 294, S. 2130–2136 BMBF (2003): Herausforderung Klimawandel, Broschüre BMU (2006a): Globaler Statusbericht Erneuerbare Energien 2005 (http://www.erneuerbareenergien.de/files/pdfs/allgemein/application/pdf/statusbericht_ee.pdf) BMU (2006b): BMU Statistik: Beitrag der Erneuerbaren Energien zur Stromerzeugung in Deutschland 1990-2005 (http://www.erneuerbare-energien.de/files/pdfs/allgemein/application/pdf/ee_strom.pdf) BMU (2006c): BMU Statusbericht: Energieversorgung für Deutschland, Statusbericht für den Energiegipfel am 3. April 2006 (www.bmu.de ) BMU Statistics (2006): Renewable energy sources in figures - national and international development 188 http://www.erneuerbareengien.de/files/english/renewable_energy/downloads/application/pdf/ broschuere_ee_zahlen_en.pdf Boberg, F., and Lundstedt, H. (2003): Solar wind electric field modulation of the NAO: A correlation analysis in the lower atmosphere, Geophys. Res. Lett. 30, No 15, 1825, S. 8-1 - 8-4 Böhm R. (2006): Homogenisierung langer Klimareihen des Hohenpeißenberg und des Al- penraums, GAW Brief (DWD) Nr. 36 (www.dwd.de/gaw) Bony, S. et al., (2006): How well do we understand and evaluate climate change feedback processes? J. Climate 19, S. 3445-3482, Böttinger, M. (2004): Das Erdsystem im Höchstleistungsrechner – Klimaprognosen, DKRZ Jahrbuch 2004 Boucher, O., Pham, M. (2002): History of sulfate aerosol radiative forcings, GRL 29, No. 9, 1308 Boucher, O. et al., (2004): Direct human influence of irrigation on atmospheric water vapour and climate, Climate Dynamics 22, Issue 6-7, S. 597 - 603 Bousquet, P., et al. (2000): Regional Changes in Carbon Dioxide Fluxes of Land and Ocean Since 1980, Science 290, No. 5495, S. 1342-1346 Bousquet, P. et al. (2006): Contribution of anthropogenic and natural sources to atmospheric methane variability. Nature 443, S. 439-443 Bradley, R. S., et al. (2001): Scope of Medieval Warming, Science 292, No. 5524, S. 2011- 2012 Brasseur, G. P., et al. (2003): Program for Integrated Earth System Network Modelling (PRISM) and the European Network for Earth System Modelling (ENES), CLIVAR Ex- changes Newsletter 8, Heft 4 Brasseur, G. P., Schmidt, H. (2004): Ozonabnahme in der Stratosphäre, Promet (DWD) 30, Nr. 3, S. 106-115 Briffa, K. R., et al. 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17 Internet Addresses

Discussion Rooms: www.real.climate.org (climate scientists) http://climatesci.atmos.colostate.edu/ www.co2science.org www.climateaudit.org www.worldclimatereport.com www.meteo.lcd.lu/globalwarming http://www.climateark.org/ http://www.climatesciencewatch.org/ http://www.worldviewofglobalwarming.org/ http://www.climatedenial.org/

Climate Criticism: http://www.tu-berlin.de/~kehl/project/lv-twk/02-intro-3-twk.htm

Observations (climate elements, greenhouse gases etc.): Carbon emissions: (http://cdiac.esd.ornl.gov/ftp/ndp030/) Greenhouse gases: (http://cdiac.esd.ornl.gov/pns/current_ghg-html) CDIAC (Carbon Dioxide Information Analysis Center), (http://gaw.kishou.go.jp/wdcgg.html) Temperature trends: (http://www.cdiac.esd.ornl.gov/trends/temp/contents.htm) Sunspots: (http://sidc.oma.be) Ice: State of the Cryosphere (http://nsidc.org/sotc/) World Glacier Inventory: (http://nsidc.org/data/g01130.html) Climate Model Intercomparison Project: (http://www-pcmdi.llnl.gov/ipcc/about_ipcc.php)

Institutions: Alfred-Wegener-Institut, Bremen: http://www.awi-bremerhaven.de/ American Meteorological Service: http://www.noaa.gov/ German Meteorological Service – Climate Information System (www.dwd.de/de/Fund/EKlima/KLIS/) German Climate Research Programme (www.deklim.de) German Computing Centre for Climate and Earth System Research (www.dkrz.de) British Meteorological Weather Service http://www.met-office.gov.uk/ European Environment Agency: http://eea.europa.eu/ European Climate Forum (www.european-climate-forum.net/) GKSS Forschungszentrum, GKSS Research Centre: http://www.gkss.de/ Hamburg Educational Server: (http://www.hamburgerbildungsserver.de/index.phtml?site=themen.klima) IPCC (Intergovernmental Panel on Climate Change) (http://www.ipcc.ch) IFM Geomar: http://www.ifm-geomar.de/ Max-Planck-Institut for Meteorology, Hamburg, MPI-M (www.mpimet.mpg.de) Meteorological Institute of the University of Hamburg: http://www.awi-bremerhaven.de/ National Academies Press, USA: http://www.nap.edu/ Potsdam Institute for Climate Impact Research (www.pik-potsdam.de) ProClim – Swiss internet portal for climate research (www.proclim.ch) Climate information: http://www.atmosphere.mpg.de/enid/ Secretariat of the UN Conventions, (official texts) (http://unfcc.int) Umweltbundesamt (Federal Environment Agency, Dessau) (www.uba.de) Wissenschaftlicher Beirat der Bundesregierung Globale Umweltveränderungen (Scientific Advisory Board of the Federal Government on Global Environmental Changes) (www.wbgu.de) UNEP-WCMC Forestry programme: http://www.unep-wcmc.org/forest/original.htm WMO: (http://www.wmo.ch/index-en.html) 209

18 Annex – Statements about Climate Change 20 July 2005: Statement for Congress from Cicerone, President, National Academy of Sci- ence, USA. Climate Change Science and Research: Recent And Upcoming Studies From The National Academies “Nearly all climate scientists today believe that much of earth’s current warming has been caused by increases in the amount of greenhouse gases in the atmosphere…”

June 2005: Joint Science Academies’ Statement: Global response to climate change. 13 national academies have postulated: ”...There is now strong evidence that significant global warming is now occurring. …We urge all nations, …, to take prompt action to reduce the causes of climate change.”

26 March 2005: Statement of 27 climate researchers from Germany, Austria and Switzerland "There is a nearly unanimous consensus in science that the anthropogenic influence on the climate fluctuations has meanwhile most probably become dominant.“

02 Dec. 2003: Two leading American scientists (Karl, Trenberth) observe: "No doubt human activity is affecting global Climate" (90 % probability)

19 Dec. 2003: AGU (American Geophysical Union) Statement on Human Impact on Climate: In the past years, a series of statements by climate scientists and their associations have been published all assuming that anthropogenic activities are highly responsible for the temperature increase of the last decades. In the following, some of the climate statements and quotations have been compiled. “human activities are increasingly altering the earth’s atmosphere”

10 Nov. 2003: Special expertise of the Scientific Advisory Board of the Federal Government (WBGU). ”2° C maximum tolerable temperature increase to avoid hazardous climate change (already 0.6° C have been reached)

01 Oct. 2003: USA: Scientists’ Statement on Climate Change. Letter of over 1,000 scientists directed to Policy makers. “The scientific consensus around climate change is robust.” “The main conclusions of the IPCC and NCR reports remain robust consensus positions supported by the vast majority of researchers in the field of climate change”

Sept. 2003: Statement of the Deutsche Meteorologische Gesellschaft (German Meteorologi- cal Society, DMG), the Österreichische Gesellschaft für Meteorologie (Austrian Society for Meteorology, ÖGM), and the Schweizerische Gesellschaft für Meteorologie (Swiss Society for Meteorology, SGM), "Even although the reasons for the observed climate changes are complicated, and the role of natural climate changes has in no case been sufficiently explained yet, there is a high probability for the global warming of the last 100 – 150 years to be caused by anthropogenic activities, in particular by the constantly rising emissions of carbon dioxide.“

09 Feb. 2003: American Meteorology Society (AMS), Climate Change Research: Issues for the Atmospheric and Related Science: ”Because human activities are contributing to climate change we have a collective responsi- bility to develop and undertake carefully considered response action”.

2001: National Academy of Science: Climate Change Science: An Analysis of some key questions, “The full IPCC Working Group Report Group I (IPCC Report 2001, Scientific Basis) is an admirable summary of research activities in climate science,” 210 13 July 2001: Amsterdam Declaration on Global Change, warning of participants of 4 international "Global Change“ research programmes against the anthropogenically caused climate changes and their impact on human health.

Oreskes writes in Science (Vol 306, Dec 2004), that the IPCC is not alone in its conclusions. In recent years, all major scientific bodies in the United States whose members' expertise bears directly on the matter have issued similar statements. This is also true for the Report of the National Academy of Sciences (2001), which states, that the scientific community currently agrees to the conclusion that the main share of the warming observed in the past 50 years is attributable to anthropogenic activities.

Furthermore, Oreskes (Professor for History of Sciences, Univ. San Diego, CA) and her staff examined the extent, to which opinions deviated in scientific studies published between 1993 and 2003 in peer-reviewed scientific journals. Of 928 studies found in the ISI database dealing with climate changes, there was no paper - according to her analysis - that did not agree to the consensus opinion. Oreskes concludes her observations by establishing that, as can be seen throughout the history of science, a scientific consensus may of course also be wrong. "But our grandchildren will surely blame us if they find that we understood the reality of anthropogenic climate change and failed to do anything about it.“

This assessment did however meet with criticism. Peiser (2005) analysed the same database and (initially) partly arrived at different results. He states that only 29 % of 1196 abstracts explicitly favoured the consensus opinion. 34 abstracts rejected the consensus opinion or questioned it, and 44 papers emphasised that natural factors play an important role in recent climate change. In the meantime, Peiser has withdrawn from his often quoted criticism: “I do not think anyone is questioning that we are in a period of global warming. Neither do I doubt that the overwhelming majority of climatologists is agreed that the current warming period is mostly due to human impact. “ - E-mail from Benny Peiser to Media Watch, 12th October, 2006 http://www.abc.net.au/mediawatch/transcripts/s1777013.htm

In the magazine "Der Spiegel", issue of January 2005, von Storch questioned that the consensus opinion ushered in the statements is correct. He takes the view that fundamental questions of the climate problems have not yet been answered. On the other hand, von Storch declared in an interview given to the Helmholtzgesellschaft in November 2005, "that at present we experience a man-made climate change." (www.helmholtz.de/de/aktuelles).

According to a survey amongst 530 climatologists effected by Bray (GKSS) in 2003, approx. one quarter of them would still question as to whether human activities are responsible for the recent climate changes (www.sepp.org/NewSEPP/Bray.htm).

In conclusion, it remains to be said that despite the many, still existing uncertainties and un- solved problems, the vast majority of climatologists agree to the so-called consensus opinion.