Polar meteorology

Understanding global impacts

WMO - No. 1013 

Polar meteorology

Understanding global impacts Photo credits

We would like to thank the following individuals and organizations for their generosity in sharing their photos and figures with WMO:

Cover, pages 3, 27, 28, 29 and 31 to 37: Christian Morel Pages 12, 15, 16, 21 and 22: International Polar Foundation Pages 4, 6, 8 and 11: G. Dargaud (International Polar Foundation) Pages 19 and 20: NASA Page 5: University of Wisconsin-Madison Page 7: Scottish Association for Marine Science Page 17: Columbia University Page 18: UNEP Pages 14 (2) and 24: Mathieu Quétu Page 25: EUMETSAT Page 26: ESA/AOES MEDIALAB (left); http:www.Firstpeople.US (right)

WMO-No. 1013 © 2007, World Meteorological Organization ISBN 92-63-11013-1

NOTE The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Secretariat of the World Meteorological Organization concerning the legal status of any country, territory, city or area, or of its authorities, or concerning the delimitations of its frontiers or boundaries. CONTENTS

Foreword ...... 2

Introduction ...... 3

Polar meteorology ...... 5

Observing the polar regions ...... 5

High-latitude weather systems ...... 8

Weather forecasting in the polar regions ...... 11

The role of the polar regions in the global climate system ...... 17

The Poles ...... 17

Links with lower latitudes ...... 17

Recent high-latitude environmental changes ...... 22

How will the polar regions change in the future? ...... 30

International Polar Year 2007-2008 ...... 37

 FOREWORD

World In recent decades, great advances have been Meteorological made in our understanding of the role of the Day (23 March) polar regions in the global climate system. celebrates the Shrinking sea-ice, melting ice sheets, the dis- date of the entry charge of glaciers and thawing of permafrost into force of are all dramatic changes that have been taking the Convention place in those regions owing to an increase which created the in global average temperature. It is evident Organization in that the increased average rate of sea-level 1950. rise resulting from the melting of ice of land origin would be dangerous for lowlands and The WMO some islands whatever their geographical Executive Council location. Ocean circulation changes may have decided that the an impact on the distribution of temperature, theme for World salinity and organic substances in tropical Meteorological areas. This would have a crucial impact on fish Day in 2007 stocks and therefore on national economies would be “Polar and livelihoods and our eating habits. That M. Jarraud, Secretary-General meteorology: is why even countries geographically far understanding removed from the Poles have a real concern global impacts”, in regarding changes in the polar environment recognition of the and are participating in the International Polar over the next century. I wish to express my importance of, and Year (IPY) 2007-2008. appreciation to the author, John Turner, as a contribution Project Leader with the British Antarctic to, the International WMO, through the National Meteorological Survey, and other contributors. Polar Year (IPY) and Hydrological Services (NMHSs) of its 2007-2008, Members, will be offering substantial con- I urge the NMHSs of all WMO Members which is being tributions to the IPY in the areas of polar having an interest in polar research and co-sponsored meteorology, oceanography, glaciology and observations to participate actively in imple- by WMO and hydrology, in terms of scientific research menting the IPY. I would also welcome the the International and observations. Ultimately, the scientific NMHSs, international organizations, non- Council for Science and operational results of the IPY will be governmental organizations and indeed all (ICSU). offering benefits to all WMO programmes who are interested in these unique parts of by generating comprehensive datasets and the globe to seize this ideal opportunity to authoritative scientific knowledge to ensure provide input to the IPY and so secure a rich the further development of environmental scientific output for the benefit of all—now monitoring and forecasting systems, includ- and in the future. ing severe weather prediction. Moreover, the IPY will provide valuable contributions to the assessment of climate change and its impacts, so the observing networks to be established or improved during the IPY period will be kept in operational mode for many years. This will be an important part of the IPY legacy to the world.

This booklet highlights the importance of the polar regions in the entire Earth system, particularly in climate. It describes some of the major environmental changes that have taken place in the Arctic and Antarctic in (M. Jarraud) recent years and considers possible changes Secretary-General

 FOREWORD INTRODUCTION

In recent years, there has been an unprec- factors such as sea-level rise and variations The polar regions edented level of interest in the climate in atmospheric and oceanic circulations. have warmed more and environmental conditions of the polar significantly than regions. The discovery of the Antarctic ozone The Greenland and Antarctic ice sheets other regions. hole, record low levels of Arctic sea ice, contain 9 and 90 per cent, respectively, of the loss of ice from the Greenland ice sheet, world’s glacier ice. If both these ice sheets Global impacts the disintegration of a number of floating melted completely, they would contribute include sea-level ice shelves around the Antarctic Peninsula 7 m and 70 m, respectively, to sea-level rise, with the risk and the high levels of aerosols reaching rise. While such a dramatic occurrence is of flooding and the Arctic, have all been reported by the not expected, even on the time-scales of even the continued media. Moreover, climate model predictions hundreds of years or millennia, the melting of existence of some indicate that high-latitude areas will warm a small fraction of this ice would nonetheless low-lying areas and more than any other region over the next have serious implications for global sea-level islands. century as a result of increasing levels of rise and ocean circulation. greenhouse gases. It remains to be seen, Local impacts— however, whether the rapid climatic fluctua- The polar regions are also characterized which are of tions in the polar regions over the last few by large areas of sea ice—the Antarctic global interest centuries and millennia are in fact a result effectively doubles in size over the year as and importance— of natural climate variability. It is important, the ocean around the continent freezes. The include threats to therefore, to try to separate the impacts of sea ice provides an effective thermal cap on biodiversity—the natural climate variability from those of the top of the ocean and the expulsion of salt survival of animal human activity. that takes place as it forms is important for and plant species. the global circulation of the ocean. At risk also is the Although the polar regions are remote from traditional way of major populated areas, they are of great Polar meteorology in this context is consid- life of indigenous significance in the global climate system; ered in a broad sense with respect both to peoples of the changes at high latitudes can have an impact the behaviour of weather systems and its Arctic, who depend on ecosystems and human society through role in the global climate system. on those animals and plants for their food, clothing, settlements, hunting and fishing weapons, etc.

  POLAR METEOROLOGY

Observing the polar regions Within the framework of the Antarctic Treaty, The Antarctic’s it focuses on the interfaces between these massive ice cap and The polar regions are some of the least well activities and other WMO Programmes, isolation from the observed areas on Earth, as far as in situ notably the World Weather Watch (WWW), rest of the planet by meteorological observations are concerned. and aims at meeting the requirements for the Southern Ocean For example, across the Antarctic, which is meteorological services as well as for envi- prevented any twice as large as the USA, there are only ronmental monitoring and climate research, permanent human 44 stations making surface meteorological in particular, the upper-air soundings of settlement prior to observations and some 14 stations launch- meteorological variables generated by the the establishment ing radiosondes (instruments carried aloft, WMO Antarctic Basic Synoptic Network. of scientific chiefly by balloon, to gather and transmit These provide vertical profiles from the sur- stations in the early meteorological data). The more southerly face to altitudes of about 25 km and even 20th century. parts of the Arctic are better served by observ- occasionally 35 km (the lower stratosphere). ing stations because of the large number of The surface and upper-air stations routinely The continents human settlements there. Over higher latitude provide coded reports that are essential for surrounding the areas, however, few data are available from global weather forecasting. The observations Arctic Ocean have human observers because of the lack of island are today sent from the polar regions via been temperate observing stations. satellite communication systems and to the enough to be home WMO Global Telecommunication System to their indigenous Through its Antarctic Activities Programme, for transfer to the main forecasting centres. populations for WMO coordinates meteorological activities Specialized data and products for various millennia. carried out by nations and groups of nations. users are generated by regional centres of the WMO Global Data-processing and Forecasting System.

Despite the harsh environmental conditions in the Antarctic and the problem of logistics, the Antarctic Basic Synoptic Network is well implemented, thanks to the efforts of National Meteorological and Hydrological Services

A 48-hour forecast from the Antarctic Mesoscale A mosaic of infra-red satellite imagery of the Antarctic Prediction System and Southern Ocean on 21 August 2006

 An automatic weather station in the Antarctic

The Antarctic (NMHSs) and the Antarctic programmes profiles (through the atmosphere in cloudy Treaty was opened of the countries which are Parties to the conditions), the extent and concentration of for signature Antarctic Treaty. Assessment of the Antarctic sea ice and winds over the ice-free ocean. on 1 December meteorological reports arriving at the main 1959 and entered centres of WMO’s Global Telecommunication The lack of in situ observations from the into force on System suggests that the percentage of polar regions led to the early deployment of 23 June 1961. reports received is close to the global aver- automatic weather stations (AWSs), which age. Most of the observations from staffed provide frequent observations and require The Global Climate stations in the Arctic and Antarctic provide a only infrequent maintenance. AWSs were Observing System significant contribution to the upper–air and first installed in the Antarctic in the mid-1980s is co-sponsored surface networks and database of the Global and have proved their worth; more observa- by WMO, the Climate Observing System. tions are now obtained from AWSs than Intergovernmental from staffed stations. In the Antarctic, most Oceanographic Because of the lack of in situ data, polar research stations are located on the coast, Commission of meteorologists have always made extensive so AWSs are essential for meteorological UNESCO, the use of data from autonomous systems and analysis in the interior. In the Arctic, they United Nations polar-orbiting satellites. Since the 1960s, are installed on the land areas surrounding Environment satellite imagery has been an important tool the Arctic Ocean in the Russian Federation, Programme and in identifying the locations of synoptic and Fenno-Scandinavia, North America and the International mesoscale (less than 1 000 km diameter) Greenland. They have proved particularly Council for weather systems over ocean and remote land valuable in Greenland, where temperatures Science. areas. Although the early imagery was of poor have risen markedly in recent years. quality with coarse horizontal resolution and few grey scales, many stations today have An AWS is a stand-alone system that typically digital receivers capable of providing high- measures surface meteorological variables, resolution images at several wavelengths. such as wind speed and direction, air tem- perature and air pressure and may measure The earliest satellite data for the polar regions additional variables such as relative humidity consisted of visible and infra-red imagery. or vertical air temperature difference. Most In recent years, however, a vast range of polar AWSs transmit data in the blind for products has been produced from active and reception by the Argos System on board passive microwave instruments that allow the polar-orbiting satellites of the US National determination of temperature and humidity Oceanic and Atmospheric Administration

 (NOAA) series or stored on a memory module requirements and experiments to be carried The World for retrieval at a later date. In the Antarctic, out. Measurements include atmospheric Climate Research some 70 AWSs currently supplement the pressure, wind speed and direction, air tem- Programme is data from staffed stations. perature and humidity at various levels above co-sponsored the surface and, in the case of buoys on ice by WMO, the To obtain data over the Arctic Ocean or in the floes, the surface temperature of the snow Intergovernmental sea-ice zone around the Antarctic, drifting or ice and snow thickness. Using the IABP Oceanographic buoys are deployed on the ice. The major data, significant warming of the Arctic in the Commission advance in the development and deployment 1980s and 1990s was detected. (UNESCO) and of drifting buoys came with the First GARP the International (Global Atmospheric Research Programme) Although some surface synoptic weather Council for Science. Global Experiment (FGGE) in 1978/1979, charts were prepared in the early part of the when over 300 systems were deployed in the 20th century, they covered mainly the more Southern Ocean to investigate atmospheric populous regions and lacked accuracy at predictability and the requirements for an high latitudes. In particular, there were very optimum observing system. Since then, many few observations over ocean areas of the different types of drifting buoy have been Antarctic; Arctic analyses were somewhat deployed in the Arctic by the International better. An increasing number of observa- Arctic Buoy Programme (IABP) and in tions became available from polar-orbiting the Southern Ocean by the International meteorological satellites in the 1970s that Programme for Antarctic Buoys (World allowed more reliable atmospheric analy- Climate Research Programme/Scientific ses in high-latitude areas. The atmospheric Committee on Antarctic Research (WCRP/ temperature sounders flown on polar- SCAR)). Currently, a number of commercial orbiting satellites since the mid-1970s were companies and research institutes manufac- of particular importance. Similar in nature ture buoys. These are of varying degrees of to radiosonde ascents, they provided profiles sophistication, from low-cost ocean drifters of temperature and humidity from the sur- with no meteorological sensors to advanced face up to the stratosphere with the broad systems making a wide range of atmospheric coverage provided by a satellite system. and oceanographic measurements. Over the last few years, the historical archive Various instruments can be attached to the of in situ and satellite observations have basic buoy platform, depending on the data been re-processed using data-assimilation

A drifting buoy on an ice floe in the Weddell Sea, Antarctic

 Meteorological techniques to produce so-called “re-analysis” measurements taken at elevated areas of the conditions at the datasets, which provide a particularly valuable Antarctic and Greenland. Meteorological Poles are different. source for investigation of climate variability conditions at the Poles are different, as the The North Pole is over the last three decades or so. The re- North Pole is located over the Arctic Ocean, located over the analysis fields for the southern hemisphere while the South Pole is on the high Antarctic Arctic Ocean, while prior to 1974, when satellite sounder data plateau. the South Pole is on became available, were poor, however, and the high Antarctic cannot be used to investigate atmospheric In the northern hemisphere, because of the plateau. circulation change. major mountain ranges of the Himalayas and the Rockies, the tropospheric flow is highly meridional with many weather systems reach- High-latitude weather systems ing high latitudes and occasionally crossing the Arctic Ocean. On the other hand, the The Arctic and Antarctic are poleward of southern hemisphere has few large, high land the main storm tracks in the northern and masses so the depressions move in a much southern hemispheres and mean sea-level more zonal track, spiralling only gradually surface-pressure charts show climatological towards the Antarctic coastal region. The fact anticyclones in these areas. Nevertheless, that the Antarctic consists of a large, high care needs to be exercised in calculating mass of ice centred near the South Pole has a atmospheric pressure at mean sea-level using large impact on the atmospheric circulation of

 The branch of physical geography which deals with the formation and features of mountains is called orography.

An active polar low with a spiral cloud pattern A polar low off the north coast of Norway with extensive convective cloud the southern hemisphere. Depressions mov- in the Arctic are primarily a winter season ing southwards from mid-latitudes tend to phenomenon. Most active polar lows have become slow moving or start to track towards a horizontal scale of 400-600 km, although the east in the Antarctic coastal region as convective systems can have smaller vortices they encounter steep mountains. There are, embedded within them. Polar lows are part therefore, few active depressions over the of the broad category of disturbances known Antarctic interior, although some depressions as polar mesocyclones, which includes the do penetrate to Dome C, South Pole or even many minor vortices observed on satellite Vostok, where the mid-tropospheric flow is imagery of the polar regions. The defini- more meridional. This appears to happen as tion of a polar low is that it should have a part of natural climate variability and can be surface wind speed of 17 m/s or stronger. detected at interior stations by a sudden, rapid Observations have indicated that they can rise of temperature, the presence of cloud and have wind speeds as high as 33 m/s. They occasionally moderate precipitation falling bring some of the worst weather to Arctic in what is a cold desert. coastal and island locations and can be a major hazard to maritime operations, as well The Antarctic coastal region between 60°S as gas and oil exploration and production and 70°S is home to many active depressions platforms. and smaller-scale lows. The occurrence of so many storms means that atmospheric pres- In the Antarctic, the air-sea temperature dif- sures are low and the zone is known as the ferences are much less than in the Arctic circumpolar trough. There is no comparable and deep convection is not found close to feature around the Arctic, where orographic the coast of the continent or at the latitude conditions are different. of the circumpolar trough. Hence, the polar lows that occur tend to be found on shallow Polar lows horizontal temperature gradients, although The most violent weather systems found in many minor polar mesocyclones appear on the Arctic are short-lived (usually less than satellite imagery. 24 hours), mesoscale polar lows, which are active depressions occurring over certain Individual polar lows are obviously impor- ice-free, maritime areas poleward of the tant in weather forecasting for the two polar polar front—the main boundary between regions but it is still unclear whether they are polar and tropical air masses. Polar lows important climatologically. With the large

 Mesoscale polar lows are referred to by a wide variety of names, including Polar lows Arctic hurricane, Arctic bomb, Arctic Polar lows were first investigated in the the systems affected coastal communities instability low, cold late 1960s when satellite imagery became of Norway and produced some of the air depression, available, but studies were hampered by most significant snowfalls over the United comma cloud and the lack of in situ observations since the Kingdom. As satellite imagery became polar mesocyclone. lows rarely crossed synoptic observing more readily available, however, polar stations. Early modelling studies frequently lows were identified in other parts of the failed to represent the systems because Arctic where the air-sea temperature dif- of their small horizontal scale and the ferences are large, including the Davis poor parameterization of some key physi- Strait/Labrador Sea, the Gulf of Alaska cal processes, such as deep convection. and the Bering Sea, the Beaufort Sea, Recently, major advances have been made north of the Russian Federation coast, the in our understanding of these systems North-West Pacific, the Sea of Japan, and as a result of campaigns in which dedi- surrounding areas. cated aircraft fly through the lows, studies using multiple sources of satellite data, While some polar lows are found in the and experiments with high-resolution, Antarctic, they develop primarily on shal- limited-area models. low horizontal temperature gradients, as there is no deep convection at high south- In the late 1960s/early 1970s, there was ern latitudes. This situation arises because debate as to whether polar lows formed and the oceanic circulation of the southern deepened in the same way as mid-latitude hemisphere is much more zonal than north depressions on horizontal temperature gra- of the Equator, and warm water masses dients or whether they were mainly associ- do not reach the Antarctic coastline. Large ated with deep Cumulonimbus clouds, air-sea temperature differences can exist rather like hurricanes. Today, we know that in the coastal polynyas (ice-free areas of there is a spectrum of disturbances ranging water within the pack ice) (see box on from the rather rare small-scale depres- page 14), but the track of air across these sions, which form on shallow temperature areas is quite short so polar lows do not gradients with a frontal structure that have time to develop. resembles a small mid-latitude cyclone, to the systems characterized by many deep Cumulonimbus clouds.

Polar lows were first investigated in the Norwegian and Barents Seas areas, where

air-sea temperature differences associated the many minor vortices at high latitudes with polar lows, coupled with the high near- can together generate sufficient heat loss surface wind speeds, surface heat fluxes from the surface of the ocean to trigger of up to 1 000 W/m2 have been recorded, downward convection, which may affect the although there are relatively few such sys- thermohaline circulation, which is driven by tems each season at a particular location. differences in ocean water density arising The question has been posed as to whether from temperature and salinity gradients.

10 This question can only be answered using This situation remained more or less modelling experiments which are currently unchanged until the International Geophysical being carried out. Year (IGY) of 1957-1958, when a number of research stations were established at high latitudes, especially across the Antarctic, with Weather forecasting in the polar many of these making routine radiosonde regions ascents. These additional data allowed more reliable surface and upper-air analyses to Although most parts of the polar regions are be prepared, although there were still few remote from the major population centres, observations over the ocean areas. there is still a need for reliable weather fore- casts. In the Arctic, forecasts are needed for Satellite imagery has been used as an aid the indigenous communities and in support of to weather forecasting since the 1960s. For maritime operations and oil and gas explora- many years, the analyses were poor at high tion and production. In the Antarctic, reliable latitudes and imagery provided the only forecasts are needed for the complex air and means of determining the “truth” regarding sea logistical operations that support research atmospheric conditions. The images were programmes and for the growing tourism used to provide early warning of approaching industry. Forecasts are also needed for field weather systems, fronts and isolated cloud- parties working in remote locations. banks, as well as supplementary information on sea-ice extent. Forecasts of the weather over the Arctic and Antarctic have been made since the first Since the late 1970s, it has been possible to expeditions, although they were poor in the determine upper-level temperature and humid- early years owing to the few observations ity profiles through the atmosphere using data available and a rudimentary understanding collected by polar-orbiting satellites. Such of the workings of high-latitude climates. objective data allowed the implementation of

11 The wind global numerical weather prediction (NWP) limited-area numerical weather prediction scatterometer is systems that could provide forecasts for models (such as the US Antarctic Mesoscale a satellite-borne several days ahead. During the 1980s, the Prediction System) are starting to predict instrument accuracy of polar forecasts from such NWP surface winds in areas of complex orography which provides systems was much lower than those for with more success. surface wind tropical and mid-latitude areas but, during the observations from 1990s, there were marked improvements as The forecasting problem is somewhat easier measurements of a result of better analysis techniques, higher in the Arctic, since much of the region is radar backscatter model horizontal resolution and additional ringed by land from which many in situ from the ocean. data from new satellite-borne instruments, meteorological observations are provided. such as the wind scatterometer. These, coupled with satellite sounder data, allow high-quality numerical analyses and Today, the forecasting problem in the Antarctic forecasts to be prepared. The relatively low is quite different over the ocean areas and orography of the Arctic also aids predict- the continent itself. Over the ocean, the NWP ability. The main exception is the interior of models have greater accuracy than in the Greenland, where the same problems apply northern hemisphere because the orography as are found on the Antarctic plateau. of the southern hemisphere is less complex. However, over the continent, and especially The forecasting process in the coastal region, sites are affected by Weather forecasting in the Arctic and Antarctic local wind systems that many global models presents a number of unique challenges cannot capture. Forecasters therefore tend compared to the extra-polar regions (see box to adopt a nowcasting approach based on on page 23). The great advances in observing satellite imagery to predict the winds up to systems and numerical weather prediction 24 hours ahead. High horizontal resolution, described above, however, have considerably

12 improved the quality of the forecasts, but data are as yet included in these models, A radiosonde is the tasks of forecasting over land and ocean the high horizontal resolution and the more a unit for use in areas are quite different. realistic orography that can be included has weather balloons the potential to give better short-term weather that measures Over ocean areas, the large amounts of satel- forecasts. various atmospheric lite sounder data that are now available mean parameters and that the meteorological analyses are of high THORPEX transmits them to a quality, despite the lack of radiosonde data. THORPEX (The Observing System Research fixed receiver. This is turn means that the NWP fields can and Predictability Experiment) is part of be used with confidence over two or three WMO’s World Weather Research Programme. Radiosondes days, and give a reasonable indication of the It provides an organizational framework that measure or broadscale developments to be expected up addresses weather forecast problems, includ- calculate the to about six days ahead. Across the Antarctic ing those in polar areas, whose solutions will following variables: continent and in the interior of Greenland, the be accelerated through international collabo- • Atmospheric lack of in situ data, the problems of deriving ration among operational forecast centres of pressure satellite temperature soundings over a high, National Meteorological and Hydrological • Altitude ice-covered surface and the complex local Services, academic institutions and users • Geographical wind and cloud systems mean that the quality of forecast products. position (latitude/ of the NWP fields drops off rapidly away longitude) from the coast. In the context of the International Polar Year • Temperature 2007-2008, THORPEX has specific research • Relative humidity A recent development has been that limited- goals (see box below). In order to assist in • Wind speed and area NWP models with high horizontal resolu- accomplishing these research goals, field direction tion are being run operationally across certain campaigns will be carried out during an IPY parts of the Antarctic. Although no additional intensive observing period.

THORPEX and the International Polar Year 2007-2008

In the context of the IPY, THORPEX seeks to:

• Address the two-way interactions of polar and sub-polar weather regimes • Assess and improve the quality of operational analyses and research reanalysis products in the polar regions • Address the improvement of data-assimilation techniques for the polar regions • Assess the skill in the prediction of polar-to-global high-impact weather events for different observing strategies in higher latitudes • Demonstrate the utility of improved utilization of ensemble weather forecast products for high-impact weather events and for IPY operations, when applicable • Develop recommendations on the design of the Global Observing System in polar regions for weather prediction

13 THORPEX is a key component of the WMO Natural Disaster Reduction Glaciers, ice shelves and icebergs and Mitigation Programme. It When Antarctic glaciers reach the coast of the continent, they begin to float and will contribute to become ice shelves, from which icebergs are then calved. Since 1974, a total of WMO’s goal to 13 500 km2 of ice shelves have disintegrated in the Antarctic Peninsula, a phenomenon halve the number linked to the regional temperature rise of more than 2°C in the past 50 years. of deaths due to natural disasters Similar break-ups in other areas could lead to increases in ice flow and cause sea- of meteorological, level to rise dramatically. The final collapse of the Larsen B platform in February 2002 hydrological and freed an additional 3 250 km2 of sea bottom of an ice cover that has been estimated climatic origin over to have been there for at least 5 000 years. the next 15 years.

The vanishing ice allows vegetal and animal plankton to invade and thrive. Studies will be carried out to determine the changes in ecosystems structured largely by ice in these areas. Researchers will monitor previously fished areas located in the western part of the Antarctic Peninsula to determine the state of stock recovery.

Much of the planned IPY-THORPEX research associated with polar and sub-polar interac- is aligned with the THORPEX focus on global- tions. Examples of research investigations to-regional influences on the evolution and include the role of Greenland’s orography predictability of weather systems and the IPY on European and African cyclonic storm objective of understanding polar-global tele- systems, the interactions between tropical, connections on all scales, and the processes middle latitude and polar processes, Rossby controlling these interactions. IPY-THORPEX wave trains excited by intense cyclogenesis will address high-impact weather forecasts, off the coast of Asia and whether anomalous the predictability, and increased knowledge open water in the vicinity of the Arctic and of related physical and dynamical processes Antarctic can lead to modifications to storm

14 THORPEX: accelerating improvements in the accuracy of one-day to two-week high- impact weather forecasts for the benefit of society, the economy and the environment

Changes in Arctic sea-ice conditions impact navigation.

tracks, storm intensity and the Ferrel/Walker will contribute to the IPY core objective of circulations. determining the present environmental status of the polar regions by quantifying their The IPY-THORPEX will also address other core spatial and temporal variability. THORPEX goals in order to contribute to the development of advanced data-assimilation The improvement in satellite assimilation and ensemble prediction systems and to over the poles afforded by this study will be contribute to the design and demonstration an observational legacy of improving our of interactive forecasting systems. These ability to predict polar weather systems, the efforts include a focused campaign over the interactions of polar processes with lower Antarctic aimed at evaluating and improving latitudes and our ability to monitor the climate satellite data-assimilation techniques, which over the poles.

15 Many animals are at risk from global warming in the polar regions, such as penguins. It behoves all nations to preserve these unique communities for the benefit of future generations.

16 THE ROLE OF THE POLAR REGIONS IN THE GLOBAL CLIMATE SYSTEM

The poles the Equator-Pole temperature difference in The climate system the south is almost 40 per cent greater than can be regarded The global climate system is driven by energy in the north, producing stronger mid-latitude as an engine, with from the Sun, most of which, at any one westerlies. the low latitude time, arrives at low latitudes. Over the year, areas being the the Equator receives about five times as The poleward atmospheric transport of heat heat source and the much heat as the Poles, creating a large is largest during winter, when there is strong polar regions the Equator-to-Pole temperature difference. The heat loss at high latitudes and the largest heat sink. atmospheric and oceanic circulations respond temperature difference between equatorial to this large horizontal temperature gradient and tropical latitudes. The principal modes by transporting heat polewards. In fact, the of variability in climate system can be regarded as an engine, the atmospheric with the low latitude areas being the heat Links with lower latitudes circulation of the source and the polar regions the heat sink. extra-tropics and The polar regions are linked to the rest of high latitudes Both the atmosphere and the oceans play the Earth’s climate system by complex paths are referred to major roles in the poleward transfer of heat, through the atmospheric flow and the ocean as the Northern with the atmosphere being responsible for circulation. The circulation of the upper lay- Hemisphere 60 per cent of the heat transport, and the ers of the ocean can change over months Annular Mode, ocean the remaining 40 per cent. In the to years, but the deep ocean and the global which is closely atmosphere, heat is transported by both the thermohaline circulation require decades related to the North depressions and the mean flow. The depres- Atlantic Oscillation sions carry warm air poleward on their eastern and the Southern sides and cold air towards lower latitudes on Hemisphere their western flanks. The atmosphere is able Annular Mode to respond relatively quickly to changes in (also known as the the high- or low-latitude heating rates, with high latitude mode storm tracks and the mean flow changing on or the Antarctic scales from days to years. Oceanic change Oscillation). takes place on much longer time-scales.

The different distribution of land masses in the northern and southern hemispheres has a major impact on the atmospheric and oceanic circulations, with the mean ocean and atmospheric flows in the south being much more zonal than in the north.

Virtually everywhere in the southern hemi- sphere, the atmospheric heat transport is greater than the contribution from the ocean while, north of the Equator, the ocean transport dominates from the Equator to 17°N. The peak of transport is found in both hemispheres close to 35° from the Equator. At those latitudes, the atmospheric component is about 78 per cent of the total in the northern hemisphere and 92 per cent in the southern hemisphere. Atmospheric conditions during the positive phase A further consequence of the different land/ (top) and negative phase (bottom) of the North Atlantic sea conditions in the two hemispheres is that Oscillation (see pages 18-20 for more details).

17 The word thermohaline is derived from the Greek words for Thermohaline circulation heat (therme) and salt (hals), which, The thermohaline circulation links the Stream) head polewards from the equato- together, determine major oceans. It plays an extremely rial Atlantic Ocean, cooling all the while the density of important part in linking the high-latitude and eventually sinking at high latitudes seawater. regions with the rest of the Earth system (forming North Atlantic Deep Water). This and provides a direct link between the dense water then flows into the ocean The thermohaline Arctic and Antarctic. basins. While the bulk of it upwells in circulation is the Southern Ocean, the oldest waters variously called the It is driven by differences in the density (with a transit time of around 1 600 years) ocean conveyor of seawater, which, in turn, are control- upwell in the North Pacific. Extensive belt, the global led by temperature and salinity. Wind- mixing therefore takes place between conveyor belt, or driven surface currents (such as the Gulf the ocean basins, reducing differences the meridional between them and making the Earth’s overturning ocean a global system. circulation. am re St Sea-to-air lf On their journey, the water masses trans- heat transfer Gu port both energy (in the form of heat) and matter (solids, dissolved substances and Atlantic Ocean Pacific gases) around the globe. As such, the Ocean state of the circulation has a large impact Indian Ocean on the climate of our planet. Warm shallow current

Cold and salty deep current

to centuries to respond (see box above). high latitudes, such as surface pressure and The most rapid links between high and low temperature, geopotential height and zonal latitudes therefore tend to be through the wind. NAM and SAM show little variability atmosphere. with height. Observational and modelling studies have shown that they contribute Over the last few years, there has been a great a large proportion of the high- and mid- deal of interest in the modes of variability of latitude climate variability on a large range high-latitude areas. These reflect the means of time-scales, with SAM being likely to drive by which high- and mid-latitude areas interact the large-scale circulation of the Southern and cover broadscale changes in atmospheric Ocean. SAM and NAM are usually defined pressure and the major storm tracks. as the mean sea-level pressure difference between 40° and 65°. The Northern Hemisphere Annular Mode (NAM) and the Southern Hemisphere Annular The North Atlantic Oscillation (NAO) is closely Mode (SAM) have zonally symmetric or annu- linked to the Arctic Oscillation and its vari- lar structures, with synchronous anomalies of ability has a major influence on the Arctic opposite sign in high and mid-latitudes. They climate. NAO is the dominant mode of winter can be seen in many parameters measured at climate variability in the North Atlantic region

18 Teleconnections are statistically significant links El Niño-Southern Oscillation between climates of different El Niño-Southern Oscillation (ENSO) is a Undercurrent) at lower levels. When these geographical areas major fluctuation of mass across the tropical “cold” conditions are pronounced, the which can be great Pacific associated with periods of “warm”, system is referred to as being in the La Niña distances apart. “cold” and intermediate conditions in the phase of the cycle, when the Australasian sea-surface temperatures (SSTs) of the convection can be marked with flooding El Niño-Southern eastern Pacific Ocean. During the more in areas such as Australia and Indonesia. Oscillation (ENSO) frequent “cold” periods, the tropical Pacific In the ocean, the upwelling of nutrient- is the largest is characterized by strong easterly trade rich water over the eastern Pacific can be climatic cycle on winds and a mean sea-level pressure dis- extensive, with consequent benefits to the Earth on decadal tribution of high pressure over the eastern fisheries of South America. and sub-decadal Pacific off South America and low pressure time-scales. It has around Indonesia. This is accompanied by During the “warm” phase of the ENSO a profound effect general ascent (descent) over the western cycle, know as El Niño, there is a reduction not only on the (eastern) Pacific and a west-to-east return in the surface pressure gradient across weather and oceanic flow at upper levels in the atmosphere, the Pacific and a weakening of the trade conditions across known as the Walker Circulation. winds. Convection over the western Pacific the tropical Pacific, decreases and, in extreme El Niño condi- where ENSO has its Such a scenario tends to give extensive tions, there can be drought in parts of origins, but also in convective precipitation over Australasia Australia. The main area of tropical convec- regions far removed and Indonesia (where SSTs are high), tion moves eastwards towards the date from the Pacific and more settled anticyclonic conditions line and SSTs rise across the central and basin. over the eastern Pacific. The strong east- eastern Pacific. Ocean currents are reduced to-west trade winds induce a westward- in strength and there is a marked reduction moving ocean current, known as the South in the upwelling off South America, with Equatorial Current, with an eastward- consequent effects on the fishing industry moving return current (the Equatorial in the area.

Visualization of an El Niño-Southern Oscillation event (June 1997)

19 The polar regions are keepers of the Earth’s climate archives. They also Polynyas act as a kind of early warning system “Polynya” is a Russian word meaning of what could be “an enclosed area of unfrozen water sur- expected by the rounded by ice”. Although polynyas can be planet as a whole ... hundreds of kilometres wide, their surface area is far less than the area of sea ice Climate changes which surrounds them. Some polynyas in the Antarctic occur at the same time and place each that affect the ice year and certain animals adapt their life shelves, sea-ice strategies to this regularity. production or the flow of cold, Polynyas teem with animal and plant life. Antarctic air It is only here, where the sea ice is absent, masses could have that the Sun’s energy directly reaches the implications for waters. Snow and ice ordinarily reflect the global ocean much of the Sun’s light energy, but the system. open waters of polynyas absorb it.

Phytoplankton in the polynya use this energy to produce a nutrient-rich grazing area for zooplankton. Feeding on these A new polynya formed in the Beaufort Sea small animals are whales and fishes that in August 2006 and continued to grow. By in turn feed seals, walruses and polar 11 September 2006, the area of open water had bears. grown to some 100 000 km2.

and its influence extends into the Arctic basin. flow down the Labrador Sea, resulting in more NAO is a large-scale oscillation in atmospheric sea ice than usual around Greenland. mass between the subtropical high close to the Azores and the low-pressure centre close In the negative phase of NAO, both the to Iceland. The index varies from year to year subtropical high and the Icelandic low are but also exhibits a tendency to remain in one weak, giving a reduced pressure gradient phase for intervals lasting several years. and fewer and weaker winter storms across the North Atlantic. There is cold air across During the positive phase of NAO, the sub- northern Europe and in the western sector of tropical high-pressure centre is stronger the Arctic, causing more extensive sea ice. than usual, while the Icelandic low is deeper. On the other hand, Greenland has milder The stronger pressure gradient results in winter temperatures. more frequent and deeper winter storms crossing the Atlantic Ocean and reaching the During El Niño events, the intense storm activ- northern parts of Europe. Europe gets warm, ity in the tropical Pacific is close to the date wet winters, but warm air is also carried into line with deep convection giving divergence the Norwegian and Barents Seas, resulting in in the upper atmosphere. This results in long less sea ice than normal. On the other hand, meteorological wave trains (Rossby waves) the deep Icelandic low gives strong northerly that travel polewards in both hemispheres

20 and provide a means for the establishment The seas around the Antarctic are particu- Evidence of of teleconnections between ENSO and the larly important because of the production of widespread climates of mid- and high-latitude areas. Antarctic bottom water—the densest water sea-ice melting In the North Pacific, a clear signal of ENSO mass found in the oceans. Antarctic bottom is corroborated warm events is transmitted northwards via water is formed by deep winter convection by a recent three- Rossby wave trains known as the Pacific in the Antarctic coastal region, particularly fold increase in North American pattern. The northernmost in the Weddell and Ross Seas, but also in freshwater content limit of this wave train can affect the climate association with other ice shelves. of the Arctic Ocean. of Alaska, USA. The water mass is formed as cold air from Sea-ice area at the The most pronounced signals of ENSO in high the Antarctic rapidly cools the surface waters, end of summer southern latitudes are found over the South- opening near-coastal polynyas (see box on (September) has East Pacific as a result of a Rossby wave page 20) and promoting downward convec- declined about train giving positive height anomalies over tion. Brine rejection during the formation 17 per cent over the Amundsen-Bellingshausen Sea during El of sea ice on the ocean surface is also very the last 25 years. Niño events and negative anomalies in the important, as is melting under the ice shelves. Regionally, this is La Niña phase of the cycle. The extra-tropical Antarctic bottom water flows out into the seen as a retreat signature can sometimes show a high degree world’s oceans and is found below 4 000 m in the ice edge of of variability between events in this area, in all the ocean basins. 300-500 km in the however. Beaufort Sea or the It flows northwards in the Atlantic Ocean, east Siberian Sea, The thermohaline circulation is the system that reaching the Arctic, where heat is released depending on the links the major oceans (see box on page 18). into the atmosphere. It can be appreciated, year.

Sea ice is important for walruses during feeding as it provides a resting place between dives and enables them to fish over a wider area.

21 Taiga: the swampy therefore, that climate changes in the Antarctic system as a source and sink of important coniferous forest that affect the ice shelves, sea-ice production greenhouse gases, which are held in the of high northern or the flow of cold, Antarctic air masses permafrost or seasonally frozen ground. The latitudes could have implications for the global ocean frozen ground of the Arctic tundra and taiga system. contains methane, ozone and carbon dioxide. Tundra: a vast, In fact, these areas contain one-third of the nearly level, treeless Changes in ocean conditions in the Arctic world’s soil-bound carbon. When permafrost Arctic region, can also have widespread implications. For melts, it releases carbon into the atmosphere usually with a example, ocean salinity anomalies in the and can contribute to increasing greenhouse- marshy surface central Arctic have been shown to propagate gas concentrations. and underlying into the Greenland Sea, where they can cause permafrost major modifications to ocean stratification. Recent high-latitude The frozen areas of Significant advances in the understanding of environmental changes the Arctic tundra the role of the Arctic in the global climate sys- and taiga contain tem were made during the years 1994-2003, In recent decades, there have been major one-third of the the decade of the World Climate Research changes in the polar environments, with rising world’s soil-bound Programme’s Arctic Climate System Study near-surface air temperatures causing large carbon. When the (ACSYS). The Arctic (and to a much lesser decreases in perennial sea-ice extent in the permafrost melts, extent the sub-Antarctic islands) plays a Arctic, a reduction in the amount of snow it releases carbon further important part in the global climate cover, melting of permafrost and decreases and methane into the atmosphere and can contribute to increasing greenhouse-gas concentrations.

The polar bear is emblematic of the Arctic region. Climate warming puts at risk his habitat, his food supply and ultimately his survival — as well as that of the indigenous human population.

22 A katabatic wind is a wind that blows down a topographic Weather forecasting problems specific to incline such as a hill, the polar regions mountain or glacier. There have been The wind field of the Antarctic is one of Nimbostratus. Under such conditions, it contrasting trends the most marked characteristics of the is often impossible for an observer to see in polar sea ice continent, with the persistent downslope small mounds or crevasses on the surface over the last couple (katabatic) winds in parts of the coastal when only a few metres away. A forecast of decades, with region being the most directionally constant of surface contrast is therefore essentially a large loss of ice on Earth. The winds are strongest during one of the type and depth of cloud to be in the Arctic and a the winter when strong radiational cooling expected at a given location. slight increase in produces a large pool of cold air on the the Antarctic. plateau to feed the katabatic wind system. A related quantity is horizontal definition, Strong katabatic winds are not found all which is the ease with which the boundary around the coastal region but are concen- between the ground and the sky can be trated in the main glacial valleys, particularly determined. The parameter is extremely around the coast of the eastern Antarctic. important for flying operations on the ice Climatology provides a good guide to where shelves and in featureless parts of the polar the strongest katabatic winds are found, regions, such as the interior Antarctic pla- but excellent forecasts are provided for teau or the centre of Greenland. In a similar the coastal region by numerical weather way to surface contrast, horizontal definition prediction techniques. is determined primarily by the type and nature of the cloud present. The worst Katabatic winds are less of a feature of the conditions are experienced when there Arctic because the mountains are lower. is a thick layer of Stratus, Altostratus or Strong katabatic winds are found in the Nimbostratus. As with surface contrast, the coastal regions of Greenland, however, forecasting of horizontal definition is carried where they can affect local communities. out once a forecast has been made of the cloud to be expected. The key elements A number of meteorological elements required are predictions of type and depth are of particular importance in the polar of cloud, plus knowledge of local orography. regions. One of these is surface contrast. Together, these allow a subjective forecast This is the ease with which features on a of the horizontal definition to be made. snow-covered surface can be distinguished, either from the air or by a surface observer. For aviation, knowledge of surface contrast is vital so that safe take-offs and landings can be made. Surface contrast is dictated primarily by cloud cover; in cloud-free conditions, the surface contrast is usually excellent because of the small amounts of aerosol that are present in the polar atmosphere and very good visibility. The greatest problems are encountered with deep, opaque layers of cloud, often in the form of featureless Stratus, Altostratus or

23 Satellites have in river and lake ice. Melting glaciers in many over a century in some areas, but only about revolutionized parts of the Arctic are contributing to rising 50 years in the Antarctic. These observa- meteorological sea-level worldwide. In areas such as Alaska, tions provide us with the most accurate science and climate melting glaciers can have pronounced regional measurements of atmospheric conditions, and environment effects through the contribution of their runoff yet the observations are widely separated monitoring. They to ocean currents and marine ecosystems in in many regions, with few observations enable scientists the Gulf of Alaska and Bering Sea. Change from over the oceans. to observe and is less evident and less widespread in the monitor the extent Antarctic than in the Arctic. Temperature of pack ice, the Analyses of surface meteorological obser- volume of ice caps, Investigating high-latitude climate change vations suggest that the near-surface air the productivity presents a number of problems. The peoples temperature of the Earth increased by of ocean waters of the Arctic have reported warmer and approximately 0.6°C over the last century. and levels of increasingly variable weather, as well as However, the pattern of surface change across stratospheric ozone. changes in terrestrial and marine ecosys- the Earth in the instrumental era is complex tems, which have had an impact on their and sensitive to the period that is examined. Some of the largest traditional way of life. Many studies highlight that some of the larg- environmental est environmental changes have taken place changes have The length of the records, however, is rather at high latitudes. taken place at high short compared to what is available in the latitudes. more populous parts of the world. Around The map of linear trends of annual surface the Arctic, the climate records extend back temperature across the Earth over the last

24 more common and temperatures are lower. In Over the next the mid-1970s the shifted phase of the Pacific century, near- Decadal Oscillation (a major climate cycle of surface air the Pacific region) resulted in a deepening temperatures are of the Aleutian Low, and warmer conditions expected to rise in the Alaskan area. more in the polar regions than in The Siberian warming on the other hand any other parts seems to be associated with the shift of the of the Earth. This North Atlantic Oscillation/Arctic Oscillation will have serious into its positive phase over recent decades, implications for the resulting in the greater transport of warm cryosphere, oceanic Atlantic air across Europe and into central and atmospheric Asia. circulations, Satellites provide invaluable environmental data, the terrestrial especially over areas where surface observations are While there were more regional/temporal environment and sparse. episodic warm events from the 1930s to the indigenous the 1950s, warm temperatures were more peoples of the general across the Arctic during the 1990s. Arctic. Surface data for 1979-1995 from the central 50 years indicates three “hot spots” over Arctic show large warming trends for spring Alaska/northern Canada, central Siberia and followed by winter, while trends are small for the Antarctic Peninsula. These areas have all summer and autumn. Surface air-temperature experienced annual mean temperature rises warming trends are greater for inland regions of more than 1.5°C over the past 50 years. than coastal/ocean regions. Siberia had warm anomalies around 1980 and the region from In the Arctic, the spatial and temporal pattern east Siberia to Canada has been warm since of temperature change has been complex. 1989. Many Arctic stations show positive Time-series of seasonal surface temperature spring anomalies for 2002–2005 and west anomalies from 59 weather stations show Greenland has been warm since 1999. In many warm and cold periods that were often addition to changes in mean temperatures, found only in limited sectors. Alaska shows a substantial decrease in the number of extremely cold days. One of the most pronounced warm periods had its peak around 1940 as evidenced by In the Antarctic, the picture of recent climate temperature records and by the limited area change is quite different, with few significant of sea ice around Iceland. Experiments with temperature changes beyond the Antarctic climate models forced by increasing levels Peninsula. Temperatures at the South Pole of greenhouse gases have not been able have dropped since the 1950s as the wester- to reproduce this warm period, suggesting lies increased around the continent with the that it may have occurred because of natural Southern Hemisphere Annular Mode shifting climate interdecadal variability. into its positive phase. There have been no significant changes at the Vostok station on The warming trend across Alaska and north- the eastern Antarctic plateau, however. ern Canada is primarily associated with a sudden warming around the mid-1970s. The Across the Antarctic peninsula, temperature climate of Alaska is strongly influenced by the changes have been quite different on the climatological low-pressure centre located eastern and western sides. The eastern warm- over the Aleutian Islands. When this low is ing has been most pronounced during the deep, Alaska comes under the influence of summer and autumn seasons, and has been warm, southerly air masses. When the low is linked to the stronger westerlies, which are a weak, then cold, northerly air masses become consequence of the changes in the Southern

25 Shrinking pack ice Hemisphere Annular Mode. During these in the Arctic has seasons, more warm air masses are crossing caused a reduction the peninsula compared to earlier decades, in the number of raising temperatures by several degrees. seals which are the Since temperatures were previously close to principal food for freezing point, this has had a major impact on polar bears. the environment, including contributing to the break-up of several ice shelves. Of course, the loss of the ice shelves does not directly affect sea-level since they were already floating on the ocean but their disintegration may result in glaciers on the eastern side of the peninsula flowing more quickly.

Temperatures on the western side of the Antarctic peninsula have risen by more than anywhere else in the southern hemisphere, analyses for the Eurasian Arctic that extend with in situ data indicating warmings of 3°C back to 1930. Some Norwegian ice charts in the annual mean and 5°C in winter tem- also exist for the North Atlantic going back peratures over the last 50 years. In this area, to the 1500s, although the data on which they there is a close association between winter are based are extremely sparse in the early season temperatures and the extent of sea years. Drawing largely on this source, the ice off the coast, with years of extensive ice WCRP ACSYS project was able to produce resulting in cold temperatures and years of a climatology of Arctic Ocean sea-ice edge little ice yielding high temperatures. The large dating back as far as 1553. warming trend in the area suggests more extensive sea ice in the 1950s and 1960s, Reliable, high horizontal resolution sea-ice although the reasons for this are not yet extent and concentration data are available understood. The higher temperatures have for the polar regions from 1978, when the been accompanied by a greater number of scanning multichannel microwave radiometer precipitation events, with a large increase in instrument was first flown on the Nimbus-7 the number of reports of summer rainfall. polar-orbiting satellite. Such data showed that, over the period 1978-1996, Arctic sea Sea ice ice decreased by 2.8 per cent per decade or Prior to the 1970s, our knowledge of sea- 34 300 km2 per year. These reductions took ice extent and concentration was mostly place in all seasons and over the year as a based on ship and aircraft observations, with whole, but the losses were greatest in the some information from coastal stations. The spring and smallest in the autumn. The great- majority of these data are from the Arctic, est losses were in the Kara and Barents Seas where it has proved possible to prepare ice with decreases of 10.5 per cent per decade. Smaller levels of ice loss have taken place in the Seas of Okhotsk and Japan (greatest in winter) and the Arctic Ocean. Lesser ice loss occurred in the Greenland Sea, Hudson Bay and the Canadian Archipelago.

Since the mid-1990s, there have been several years with record low summer-ice extents. Data from the US National Snow and Ice Data Center indicate a September decline of more than 8 per cent per decade from 1979 to 2005. Polar ice cover as seen by satellite Based on the frequency of near-record low ice

26 extents, it is likely that the Arctic Sea is on an the 1970s, when reliable satellite passive The Antarctic has accelerating, long-term decline. In addition, microwave observations became available. no permanent the recent ice minimum was believed to be These data show that, for the period 1979- human residents lower than the Arctic ice minima of the 1930s 1998, Antarctic sea ice as a whole increased and has never had and 1940s. by 11 180 km2 per year or 0.98 per cent per an indigenous decade. Regionally, the trends in extent were population. Only The winter of 2004/2005 was remarkable positive in the Weddell Sea, Pacific Ocean certain plants and in that sea-ice recovery during the season and Ross Sea sectors, slightly negative in the animals can survive was the smallest in the satellite record. Indian Ocean sector and strongly negative in there, including As temperatures dropped over the winter, the Bellingshausen-Amundsen Seas. This is penguins, fur seals, sea ice formed but, with the exception of consistent with the ongoing warming on the mosses, lichens and May 2005, every month from December western side of the Antarctic Peninsula, which algae. 2004 set a new record low ice extent for is closely coupled with the oceanic conditions that month. September 2005 saw a new of the Amundsen-Bellingshausen Sea. For all The Arctic is mostly record minimum in Arctic sea-ice extent sectors, the sea-ice increases occurred in all a vast, ice-covered surpassing the previous record low in 2002. seasons, with the largest increase during the ocean, surrounded On 21 September 2005, the five-day running autumn. From region to region, the trends by treeless, frozen mean sea-ice extent dropped to 5.32 mil- are different across the seasons. ground. It teems lion km2, the lowest ever observed in the with life, including satellite record, starting in 1978. All four years There are only limited data available on sea-ice organisms living 2002-2005 had ice extents approximately thickness, but data from a 1 000 km transect in the ice, fish and 20 per cent less than the 1978-2000 mean, in two summer cruises in 1958 and 1970 sug- marine mammals, with the loss of sea ice amounting to approxi- gested that the draft had decreased by 0.2 m birds, land animals mately 1.3 million km2. in the transpolar drift stream and the Eurasian and human basin and by 0.7 m in the Canadian Basin. societies. The extent and concentration of Antarctic There is also evidence of sea-ice thinning of sea ice are known with confidence only since 0.8 m over 1976-1987 between Fram Strait

27 Rising and the Pole and of 2.2 m north of Greenland. temperatures are Upward-looking sonar measurements of affecting penguin sea-ice draft from submarines provide a populations with record extending back into the 1950s. These growth occurring have provided the first persuasive evidence in some parts of large-scale thinning over the entire Arctic and decline in basin. Such data showed that, between 1958 others, especially and 1976 and between 1993 and 1997, the where the food mean ice draft at the end of the melt season supply—krill— is had decreased in most deep water parts of disappearing. the Arctic Ocean, from 3.1 m in the early period to 1.8 m in the 1990s, i.e. by about Oil pipelines 1.3 m or 40 per cent. across areas of permafrost have Permafrost fractured, resulting Loss of permafrost in the Arctic is already in significant having a profound effect on the environment pollution and because of the severe damage that can be year. This has resulted in a small overall mass environmental caused to buildings reliant on permafrost for gain of 11 Gt per year, which is equivalent to damage. solid foundations. The trans-Arctic pipeline, a drop of -0.03 mm per year in sea-level. which runs for some 1 287 km across Alaska, was a hugely expensive enterprise, but breaks The west Antarctic ice sheet is losing mass at in the pipeline and other repair costs due to a rate of -47 Gt per year, while the ice sheet melting permafrost could become significant. in the eastern Antarctic shows a small mass The near-term risk of disruption to opera- gain of +16 Gt per year. The combined net tions of the pipeline is judged to be small, change has been -31 Gt per year or an increase although costly increases in maintenance due in sea-level of +0.08 mm per year. to increased ground instability are likely. We can expect to see increases in such potentially This is of particular interest, since much of it damaging slumping of land in the coming is grounded below sea-level. A complete loss decades. of the west Antarctic ice sheet would result in a 5 m sea-level rise so there is obvious The ice sheets and sea-level concern over the disintegration of even a The altimeters that have been flown since small section. Satellite data have recently the early 1990s on polar-orbiting satellites revealed a thinning of part of the ice sheet allow us to determine the height of major in the vicinity of Pine Island glacier. This is ice sheets and therefore to investigate the the largest glacier in the western Antarctic. question of mass balance—whether the ice It is up to 2 500 m thick and is grounded over sheets are growing or shrinking. The mass 1 500 m below sea-level. In the eight years balance of an ice sheet is dependent on a from 1992, the glacier retreated inland by over number of factors, including the snow that 5 km with the loss of 31 km3 of ice. The loss of falls on it, the amount of snow that is blown ice from the Pine Island and Thwaites glacier into the ocean, the loss of mass via iceberg basins are probably ice-dynamic responses calving and the isostatic adjustment. to long-term climate change and maybe also to past removal of their adjacent ice shelves. Between 1992 and 2002, the Greenland ice If the present rate of thinning continues, it sheet showed a mixed pattern of thickening is thought that the whole Pine Island glacier and thinning. Above 1 200 m elevation, there could be lost to the ocean within a few hun- has been thickening of 4 cm per year and ice dred years. An important research target growth of 53 gigatonnes (Gt) per year. Below must be to understand why this glacier is that elevation, there has been thinning of currently shrinking, whether this is a result 21 cm per year and a shrinkage of 42 Gt per of anthropogenic activity and whether, in a

28 warming world, the thinning of other glaciers November or into December, the ozone hole Four million could start to accelerate and drain more can last several months. indigenous peoples ice from the interior of the ice sheet with live on eight million consequent impacts on sea-level. The Antarctic ozone hole developed because square kilometres of of emissions, mainly in the northern hemi- the habitable Arctic Since 1992, global mean sea-level has been sphere, of chlorofluorocarbons (CFCs) and landmass. rising at a rate of 3.2 ± 0.4 mm per year, halons. These gases were widely used in compared to 1.7 ± 0.3 mm per year in the refrigeration, as industrial solvents and for Many studies previous century. This is faster than the rate fire control. If the provisions of the Montreal highlight the of 1 mm per year that has characterized the Protocol on Substances that Deplete the vulnerability of last 5 000 years. Sea-level rise is a result of Ozone Layer of 1987 are strengthened and the Greenland ice thermal expansion of the ocean, increased followed, and according to the UNEP/WMO sheet in a world river flow into the ocean, changes in precipita- “Scientific Assessment of Ozone Depletion: of increasing air tion/evaporation and loss of ice from the ice 2006”, the ozone layer over the mid-latitudes temperatures. sheets. The exact reasons for the current rise should recover by approximately the middle of in sea-level are not known and are a major this century. Over the Antarctic, the recovery If sea-level topic of research. would take approximately 15 years longer. continues to rise at Currently, it seems to have stabilized, with its present rate or The Antarctic ozone hole some variation from year to year, depending more, it will pose Ozone is an extremely important gas in the on atmospheric conditions. a very significant stratosphere as it absorbs solar ultraviolet problem for low- (UV) light, protecting humans and other ele- While the Antarctic ozone hole is present, lying areas across ments of the biosphere. The total amount of there are increased levels of ultraviolet the world. ozone through the depth of the atmosphere radiation at the surface of the continent, was first measured in the Antarctic during which can be a hazard to humans and biota. the IGY (1957-1958) by surface-based instru- Reduced levels of ozone can also have an ments. These showed that typical values impact on lower latitudes. The polar vortex for the total ozone amount were around 300 can frequently become elongated and extend Dobson Units (DU), which corresponds to a over the southern part of South America and layer of ozone 3 mm thick at the surface. Australia, resulting in increased UV at the surface there. Many newspapers in these The seasonal cycle of ozone in the Antarctic regions provide reports and predictions of is linked to the development and breakdown UV levels to alert the community to take of the winter circumpolar vortex, which is precautions and use sun block. the strong circulation around high southern latitudes. Historically, ozone values within the vortex were around 300 DU at the begin- ning of the winter and similar at the end. During the winter, ozone amounts build up in a circumpolar belt just outside the vor- tex, due to transport of ozone from source regions in the tropics. Since the mid-1970s, an increasingly different pattern of behaviour has been observed—the Antarctic ozone hole. At the end of winter, values were found to be around 10 per cent lower than they were in the 1970s and they then dropped about 1 per cent per day to reach around 100 DU at the end of September. Values then slowly began to recover as the stratosphere warmed. Because the spring warming in the stratosphere is often delayed to the end of

29 The ozone layer protects life on Earth by blocking harmful ultraviolet The Antarctic ozone hole in 2006 rays from the Sun. The “ozone hole” is a severe depletion From 21 to 30 September 2006, the average of the ozone layer area of the Antarctic ozone hole was the high above the largest ever observed, breaking records Antarctic. for both area and depth. A little over a week after the ozone hole sustained its The 1987 Montreal new record high for average area, satellites Protocol to the and balloon-based instruments recorded Vienna Convention the lowest concentrations of ozone ever for the Protection observed over the Antarctic, making the of the Ozone Layer ozone hole the deepest it had ever been. (1985) banned ozone-depleting The new record set in 2006, by contrast, chemicals, but the was for the largest average area over an long lifetime of 11-day period, indicating that the hole those chemicals stayed larger for longer than it ever has means that the before. The Antarctic ozone hole on 24 September 2006. The ozone layer will not blues and purples indicate low ozone levels, while recover for several While human-produced compounds break greens, yellows and red point to higher ozone levels. decades. down the ozone hole by releasing chlorine and bromine gases into the atmosphere, the The annual temperature of the Antarctic stratosphere assessments of causes the severity of the ozone hole to Depletion of the Arctic ozone layer has also the state of the vary from year to year. Colder-than-average been observed, albeit to a lesser extent, ozone layer over temperatures result in larger and deeper because the temperatures in the lower the Antarctic and ozone holes, while warmer temperatures stratosphere there usually remain higher Arctic are based lead to smaller ones. In 2006, temperatures than those over the Antarctic. Ozone deple- on data collected plunged well below average, hovering tion is a concern in the Arctic, however, by WMO’s Global near or dipping below record-lows. These because of the human settlements there Atmosphere Watch. unusually cold temperatures increased the and the risk to the fish and animal life which During the Antarctic size of the ozone hole. is their traditional source of food. ozone hole season from late August through November, WMO issues bi-weekly bulletins on the state of How will the polar regions to predict atmospheric conditions that led the ozone layer. change in the future? in recent years to the dramatic break-up of More information Antarctic ice shelves. Furthermore, the vari- can be found at: Possible consequences for the rest of ous models have a high degree of variability http://www.wmo. the globe in their predictions. Research is needed to int/web/arep/ozone. The main tools we have for predicting how the refine their outputs. html. climate of the Earth will evolve are coupled atmosphere-ocean climate models. Yet cur- Atmospheric circulation rent climate models do not work well in the Model predictions suggest that, with increas- polar regions in trying to simulate the climate ing levels of greenhouse gases, the Southern of the 20th century. For example, they failed Hemisphere Annular Mode and the Northern

30 Hemisphere Annular Mode may be in their For the Arctic, a major focus of research has The IPCC has positive phase for a greater length of time. been the Arctic Climate Impact Assessment, estimated that, This will result in lower atmospheric pres- which involved hundreds of research scien- over the period sures over the Arctic and Antarctic and higher tists. Based on the results from an average of 1990-2100, globally pressures at mid-latitudes. With the greater the output from five climate models, which averaged surface pressure gradient between the mid-latitudes were also used for the IPCC, temperature temperatures will and the Poles, there will be an increase in the projections were produced for the next cen- rise by 1.4-5.8°C. strength of mid-latitude westerly winds. tury. The models all predicted a steady rise in annual mean temperature with, on average, It has also estimated Temperature temperatures being 4°C higher by 2100. that, by 2100, sea- The Intergovernmental Panel on Climate level may have risen Change (IPCC) Third Assessment Report The models suggest the largest temperature by between 0.09 (2001) estimated that, over the period 1990- increases will be in autumn and winter after and 0.88 m. 2100, globally averaged surface temperatures much of the Arctic’s sea ice has either gone will rise by 1.4-5.8°C. This range of estimates or thinned. The albedo feedback associated Albedo: the ratio of comes from the outputs of 35 greenhouse-gas with retreating sea ice dominates the signal the outgoing solar emission scenarios and a number of climate of high-latitude climate warming. radiation reflected models. by an object to the With rising temperatures, there will be a incoming solar The model runs for the IPCC’s Fourth northward shift of the Arctic climatic zones radiation incident Assessment Report suggest that, with an with a poleward extension of the boreal upon it. increase in greenhouse gases of 1 per cent per forests and the treeline. This will result in a year, annual mean surface temperatures in the transformation of Arctic landscapes, with the Antarctic sea-ice zone over the 21st century northern edge of the boreal forest advancing would increase by 0.2-0.3°C per decade. into the area now covered by tundra. In areas There would be a corresponding decrease in such as Alaska there are fears that there will the extent of sea ice. Large parts of the high be a loss of the moisture needed for forest interior of the Antarctic would experience growth, a rise in tree mortality caused by inva- surface temperature rises of more than 0.3°C sions of insects, increased risk of large fires per decade. This would weaken the katabatic and detrimental changes to the reproduction winds, especially in the summer season. of some trees, such as white spruce.

31 The Arctic Council Across the Antarctic, many mammals and Sea ice is a grouping of plant species require specific climatic condi- Because sea-surface temperatures are the eight countries tions in which to flourish, with temperature increasing, the extent of both Arctic and that have territory and the amount of liquid precipitation being Antarctic sea is expected to decrease over the in the Arctic: particularly important, although the level of next century. It is thought that this process Canada, Denmark UV-B radiation is also a significant factor. will be amplified by feedbacks in the Arctic, (Greenland, Faeroe The amount of UV-B radiation received in the with some climate models predicting that all Islands), Finland, spring has increased markedly in recent years summer season sea ice will disappear by the Iceland, Norway, the with the appearance of the Antarctic ozone second half of the 21st century. Russian Federation, hole, with consequent impact on the biota. Sweden and the Increasing temperatures would extend the Sea-ice retreat will allow larger storm surges USA. active season, boost development rates and to develop in larger areas of open water, reduce the life cycle duration. In addition, there increasing erosion through greater wave The focus of the would be reduced stress tolerance, altered activity. There would also be sedimentation Arctic Council is distribution of species and exotic coloniza- and the risk of flooding in coastal areas. the environment tion. An increase in water availability would and sustainable create an extended active season, further Although loss of Arctic sea ice could have development. the local distribution of species and expose serious implications for the ocean circulation, new ground for colonization. Meanwhile, an there could be some benefits in terms of http://www.arctic- increase in UV-B radiation could alter resource navigation around the northern parts of the council.org/ allocation, damage cellular structures and Russian Federation and Canada. A longer ice- impact the food chain. free summer season could provide substantial

32 of thaw water and the expansion of thaw Indigenous lakes, grasslands and wetlands. This will peoples of the result in changes to habitats and ecosystems, Arctic include the such as loss of habitat for caribou and ter- Aleut, Athabaskan, restrial birds and mammals—but there will Gwich’in, Inuit and be additional habitat for aquatic birds and Saami. mammals. Indigenous leaders Loss of permafrost will also result in increased have called on the erosion and soil instability, especially on the Arctic Council to coast and along the banks of rivers. This could develop an impacts result in the blocking of streams that are and adaptation important for salmon spawning. There could programme that also be increased occurrence of landslides would include and development of talik (a year-round thawed community-based layer of what was formerly permafrost) and pilot projects on increased water table depth. Some of the adaptation, and major impacts on the community could be that would stress through damage to buildings, roads and other work on education, infrastructure. outreach and communications, The melting of Arctic permafrost has serious and benefits for marine transport and offshore gas implications for the carbon cycle and the capacity-building. and oil operations, which could have major levels of greenhouse gases in the atmosphere. implications for international trade. In the past, permafrost has been a sink of car- Salekhard (Russian bon, which is locked into the frozen ground. Federation) is the Loss of sea ice around the Antarctic threatens However, with melting and the resulting only city in the large-scale changes in marine ecosystems, warmer soils, there will be an increase in world situated on including threats to populations of marine speed of decomposition and the release of the polar circle. mammals, such as penguins and seals. Of the the greenhouse gases carbon dioxide and six species of Antarctic seal, four breed on the methane into the atmosphere. sea ice during spring and may be affected by major reductions in sea-ice extent. At present, The WCRP Climate and Cryosphere (CliC) the Antarctic sea ice shelters the larvae of Project, the International Permafrost the vast krill population that feeds countless Association, and the Global Carbon Project seabirds, seals and whales; serious reductions of the Earth System Science Partnership in the extent of sea ice would diminish the are currently undertaking a study aimed at krill population, with subsequent effects on assessing more exactly the carbon pools in higher predators. permafrost and the potential impacts of their release into the atmosphere in a warmer Permafrost climate. Permafrost is highly sensitive to long-term atmospheric warming, so there will be a The oceans progressive thaw of the permanently and Predicting how the ocean circulation will seasonally frozen ground around the Arctic. evolve in the next century is extremely dif- The IPCC has estimated that, under some ficult. Because the ocean is seriously under- greenhouse-gas emission scenarios, 90 per sampled compared with the atmosphere, cent of the upper layer of Arctic permafrost we still have a poor understanding of recent may thaw. ocean variability. Nevertheless, some rea- sonable predictions can be made. In the The loss of permafrost will bring destruction Antarctic, with the Southern Hemisphere of trees and loss of boreal forests, the release Annular Mode being in its more positive

33 In October 2006, phase and the westerlies being stronger, it The ice sheets and sea-level the Russian is expected that the Antarctic circumpolar With rising surface temperatures over the next Association of current will strengthen. century, it is estimated that glaciers, ice caps Indigenous Peoples and snow cover will all contract. The extent of the North told The Antarctic coastal region is one of the to which they will do so, and how fast it will the Arctic Council primary areas for the production of bottom happen in different regions, is still a matter that development water by the sinking of cold dense water for calculation and debate. It is very unlikely pressures and on continental shelves. These dense cold that there will be a major disintegration of pollution were waters carry abundant oxygen into the ocean the main Antarctic ice sheet during the next threatening reindeer deeps, thereby cooling and ventilating deep few centuries but some parts of the Antarctic pastures, hunting ocean space. With the production of less have shown rapid glaciological changes over and fishing activities sea ice being likely over the next century, it the last few years, indicating a sensitivity to and sacred sites. seems probable that less bottom water will climatic factors. Most of the main Antarctic be produced, raising the concern that the ice sheet is too cold for widespread surface deep oceans may warm. melting and it is expected that it will gain ice through increased snowfall over the next In the Arctic the loss of sea ice, increased river century, which will act to reduce global sea- runoff, precipitation, melting of the Greenland level by about 10 cm. In response to further ice sheet and the attendant freshening of loss of the ice shelves by ocean warming or the waters in the upper layer of the ocean to surface melting at the margins, however, will similarly mean less production of the there could be an acceleration of the ice North Atlantic deep water that feeds the flow from the interior, which is currently Antarctic region through the global thermo- dammed by coastal ice shelves. The impact of haline conveyor belt. Thus both Arctic and such effects could offset or outweigh greater Antarctic processes will combine to reduce snowfall across the continent. the intensity of the thermohaline circulation. That reduction may, in turn, weaken the Gulf The loss of ice shelves around the Antarctic Stream and North Atlantic Drift. This has the peninsula in recent years has often been potential to seriously affect the climate of reported and attributed to anthropogenic northern Europe, possibly lowering surface activity. There is certainly evidence that the temperatures by several degrees. warming during the summer on the eastern

34 side of the peninsula is, at least in part, a result addition, there could be a greater amount The peoples of of atmospheric circulation changes associated of iceberg calving. At the edge of the ice the Arctic have with “global warming”. If greenhouse gas sheet it is expected that the loss of mass reported warmer levels continue to increase, we may well see through runoff will exceed the gain from and increasingly further loss of ice shelves in this region. Of greater precipitation. Experts also predict variable weather, course, ice shelves are already floating on the an overall loss of ice, which will result in a as well as changes ocean and their loss does not contribute to change of sea-level of -0.02 to 0.09 m. This in terrestrial sea-level rise. It is at present unclear whether compares to the contribution to sea-level and marine the ice streams that flow into the ice shelves rise from the Antarctic, which is estimated ecosystems, which will accelerate once the shelves have disap- at -0.17 to +0.02 m. have had an impact peared, so leading to a more rapid draining on their traditional of ice from the interior of the Antarctic. There As near-surface air temperatures increase way of life. is evidence from the peninsula that some 87 worldwide, a thermal expansion of the oceans per cent of the glaciers there have shown will lead to a rise in sea-level estimated at signs of retreating over the past 50 years. 0.11-0.43 m. This will be augmented or miti- This pattern seems likely to continue with gated by contributions from the ice caps, as continued warming. discussed above. There will also be contribu- tions from melting glaciers, which have been Over the next century, major changes in the estimated at 0.01-0.23 m. Overall, the IPCC Greenland ice sheet are expected. Higher has estimated that, by 2100, sea-level may air temperatures are likely to trigger greater have risen by between 0.09 and 0.88 m. snowfall over the high, interior parts, increas- ing surface elevations. At lower levels, on the If sea-level continues to rise at its present rate fringes of Greenland, warmer conditions will or more, it will pose a very significant problem melt the ice and prompt increased runoff. In for low-lying areas across the world.

35 36 INTERNATIONAL POLAR YEAR 2007-2008

Despite a great deal of research into the will be concentrated on the high latitudes, The International polar regions over recent decades, there are but studies in any Earth region relevant to Polar 2007-2008 still large gaps in our knowledge about how the understanding of polar processes or will emphasize the polar climate operates and its interaction phenomena will also be encouraged. To central importance with ecosystems, polar environments and ensure that researchers have the opportunity of the polar societies. We therefore need a better pic- to work in both polar regions in summer regions as integral ture of conditions at the Poles and how they and winter if they wish, the Polar Year will and sensitive interact with and influence the atmosphere, actually run for two years from March 2007 components of the oceans and land masses. This will be obtained to March 2009. Earth system. during the International Polar Year (IPY), 2007-2008, a major international focused The first International Polar Year took place in The IPY will also research programme that was initiated by the 1882/1883. Since that time, there have been a address historical International Council for Science (ICSU) and number of major international science initia- weather and climate the World Meteorological Organization. tives at high latitudes, including the second records, human International Polar Year (1932/1933), all of health impacts The fundamental concept of the IPY 2007- which have had a major influence in improv- and community 2008 is as an intensive burst of internation- ing our understanding of global processes in sustainability; ally coordinated, interdisciplinary, scientific these important areas. These initiatives have and human research and observation in the Earth’s all involved intense periods of data collection, and ecosystem polar regions. The main geographic focus interdisciplinary research and the establish- vulnerability to ment of archives that indicate the state of extreme weather the polar regions. The last major initiative events and natural was the International Geophysical Year (IGY) disasters. in 1957/1958, in the pre-satellite era, which involved 80 000 scientists from 67 countries. The IGY involved unprecedented exploration and produced unexpected discoveries in many fields of research. It was during this period that many of the Antarctic research stations that exist today were established. The IGY also gave rise to the formulation of the Antarctic Treaty in 1959 and its ratification in 1961.

Today, technological developments, such as polar-orbiting satellites, automatic weather stations and autonomous vehicles offer great opportunities for further increase in our understanding of polar systems. The upcoming IPY 2007-2008 also offers an opportunity to engage the next generation of young Earth system scientists and to raise the profile of research in the polar regions with the public.

IPY 2007-2008 has attracted great interest from scientists working in many disciplines and nationalities. In response to a call by the ICSU/WMO Joint Committee for IPY, scientists have already planned and proposed more than 200 complex, international, inter- disciplinary projects addressing a wide range

37 “Remote and harsh, polar regions are nonetheless the barometers of African involvement in International Polar global warming and the water stored in Year (IPY) 2007-2008 their vast amounts of ice has significant The Regional Workshop on African Involvement in IPY 2007-2008 and International implications for Heliophysical Year was held in Cape Town, South Africa, in October 2006 with the the entire planet. support of the ICSU Regional Office and the South African National Foundation for The launch of Research. The representative of the International Programme Office for IPY made a International Polar presentation on International Opportunities from the IPY. Year 2007–2008 comes at a The audience was primarily South African scientists and research council repre- propitious time and sentatives but also included representation from several other African countries, will provide a vital including Kenya, Nigeria, Malawi, the United Republic of Tanzania and Zambia. There heritage of scientific was obvious enthusiasm for the IPY and outcomes from the meeting included the knowledge for intention to establish a Website for IPY that could represent the interests of African generations to countries. come.” (IPY IPO Newsletter, November 2006, Issue No. 2) (Michel Jarraud, Secretary-General, WMO)

“The scientific of physical, biological and social research The urgency and complexity of changes in the community stands topics in the polar regions. polar regions demand a broad and integrated ready ... to gather scientific approach. These collaborations and as much data about The National Meteorological and Hydrological coalitions will stimulate new data access and the effects of global Services of countries having an interest in the exchange practices, new academic courses warming on polar Arctic and the Antarctic are actively involved in and new forms and forums for scientific areas as quickly as the IPY preparation and implementation. It is discourse. In its total science and outreach possible—changes envisaged that the IPY will involve more than effort, IPY will represent a large step forward in these regions 50 000 individuals from more than 60 nations. in making science available and accessible will have a massive Climate change research, weather forecasting to the general public. influence on the and establishing better observing systems well-being of the are some of the priorities. Moreover, IPY will rest of the planet.” develop a unique legacy of discovery, data, observing systems and international coopera- (David Carlson, tion among the geophysical, biological and Director of the social sciences. International Polar Programme Office (IPO) for IPY)

38

For more information, please contact: World Meteorological Organization 7 bis, avenue de la Paix – P.O. Box 2300 – CH 1211 Geneva 2 – Switzerland Tel.: +41 (0) 22 730 83 14 – Fax: +41 (0) 22 730 80 27 E-mail: [email protected] – Website: www.wmo.int