Changes in the Biosphere Denef, Januari 2014
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Data collection and presentation by Carl Changes in the biosphere Denef, Januari 2014 1 Land cover Plants Marine life Land life Humans Effect of land cover change Humans have changed the type of the vegetation (‘land cover’) in many regions and this can affect the physical properties of land surface, such as surface albedo. Albedo of agricultural land is very different from that of a forest. Forest albedo is lower than that of open land because the greater leaf area of a forest and multiple reflections within the canopy result in a higher fraction of incident solar radiation being absorbed. The differences can be accentuated when snow is present, because open land can entirely be snow-covered and hence is highly reflective, while trees remain exposed above the snow and are less reflective. Surface albedo change may therefore provide the dominant influence of mid- and high- latitude land cover change on climate. Surface albedo can also be modified by the settling of anthropogenic aerosols on the ground, especially black carbon on snow (see slides on ‘Changes in the Cryosphere’). Land cover change can also affect evaporation, transpiration, and the surface roughness. These changes affect air temperature and humidity near the ground, and modify precipitation and wind speed. Anthropogenic land cover change relative to the potential natural vegetation (PNV), was estimated by IPCC to exert a negative radiative forcing of –0.4 to –0.2 W/m2, thus, slightly antagonizing global warming. In contrast, deforestation reduces evaporation in summer, bringing a warming effect. 2 In 1750, ~8 million km2 (6 to 7% of the global land surface) were used for crops and pasture, while forest cover had decreased by ~11 million km2 . By 1990, croplands and pasture covered ~50 million km2 (~37% of global land). Over the last century croplands were abandoned along the eastern USA, while the eastern forests regenerated. However, deforestation is occurring more rapidly in the tropics. In the 1990s, net removal of tropical forest increased in Africa and Asia. Latin America, Africa and South and Southeast Asia showed exponential increases in cropland in the last 50 years. With tropical deforestation becoming more significant in recent decades, warming due to reduced evaporation may globally become more significant than increased surface albedo of cropland and pasture surface change. Land change may then result in a net warming instead of a small cooling. 3 IPCC AR4-I Figure 2.15 4 Forest plant diseases and wildfires The response of boreal forests to global warming is 1) a migration northward and 2) a transition from forest to woodland or grassland in dry southern edges of continental interiors. This leads to an overall increase in herbaceous vegetation. Changes in climate together with the increasing stress from invasive species, are creating conditions conducive for many forest plant diseases. Observations indicate the occurrence of diseases from pathogenic fungi, bacteria, viruses, and other microorganisms. The temperature and moisture conditions, interacting with seasonal phenology, determine infection severity and distribution. Extreme weather, such as drought in regions with low soil moisture, can kill large expanses of trees. Desiccation of saplings with shallow roots in the top soil layers, due to summer drought, suppress forest reproduction. Jizera Mountains forest dieback in Central Europe 5 Alaska yellow-cedar decline is drought-related. A weak native pathogen causes red band needle blight [Dothistroma septosporum]. An aggressive nonnative pathogen causes sudden oak death [Phytophthora ramorum]). In California and Oregon, sudden oak death rates abruptly increased and then subsided, the patterm being driven by heavy rains and extended wet weather during warm periods. Infected trees suffer a reduced capacity to manage water, but survive until high temperatures and extended dry periods overwhelm their vascular capability, resulting in death. Two cycles of this pattern have been noted in California: 1998-2001 and 2005 -2008 (Frankel 2007). The Bay Area experienced an all-time record for rainy days in March 2006, followed in July by the longest string of hot weather ever recorded. The Amazon rainforest. The strongest growth in the Amazon rainforest occurs during the dry season as there is strong insolation, with water drawn from underground that stores the previous wet season’s rainfall. In 2005, 1,900,000 km2 of rainforest experienced the worst drought in 100 years.[59] Woods Hole Research Center showed that the forest could survive only three years of drought.[61][62] Scientists at the Brazilian National Institute of Amazonian Research argue that this drought response, coupled with the effects of deforestation by humans, are pushing the rainforest towards a "tipping point" where it would start to die on a centennial timescale. In the worst case the forest may turn into savanna or desert, with catastrophic consequences for the World's climate. However, the IPCC AR5 report is less pessimistic on this issue. In 2010 the Amazon rainforest experienced another severe 2 drought over 3,000,000 km . In a typical year the Amazon forest absorbs 1.5 Gt of CO2; instead 8 Gt [64][65] less CO2 was captured. 6 Wildfires Wildfires depend on vegetation density, temperature, relative humidity, precipitation, lightning, anthropogenic ignition sources, land-use and population density and fire suppression capacities. Wildfire incidence in the past can be reconstructed from sedimentary charcoal and ice core methane in database records, and from models, built on the above parameters. As shown here, there is a rise in the incidence of large fires from 1800. Damaged acres per fire also increased during the last 2 decades (see Figure). The interrelated nature of forest fires, deforestation by humans, drought, and warming may initiate non-linear devastating effects in the future. Source source 7 Marine life When CO2 dissolves in water (aq) the following dissociations and chemical aquilibria exist: – + About 90% of the dissolved inorganic carbon occurs as HCO3 and H ions. The latter react 2– with ocean CO3 ions in an equilibrium: 2– 2+ The CO3 ions make an equilibrium with Ca ions and solid CaCO3 which is the building block of shells and skeletons of marine species: 2– As a result, CO3 concentrations decrease. Many calcifying species such as planktonic coccolithophores, pteropods, clams, oysters, mussels and corals may be adversely affected by a decreased capability to produce their shells or skeletons. Fish and shellfish will also be negatively impacted. Other consequences are depression of metabolic rates in jumbo squid,[7] depression of immune responses of blue mussels,[8] and coral bleaching. On the basis of our present understandings, the potential for environmental and economic risks is high (IPCC AR5: Cooley et al., 2009). Ocean acidification may also generate genome-wide changes in purple sea urchins. When tested in culture under different CO2 levels, genetic changes occurred in genes for biomineralization, lipid metabolism, and ion homeostasis, gene classes that build skeletons and interact in pH regulation[Ref] . 8 Coral rifs The majority of coral rifs is located in ocean zones where pH values are lowest and thus they suffer the most. The Figure shows changes in decadal mean pH at the sea surface centered around the years 1875 (top) and 1995 (bottom), as modelled with CCSM3. The regional distribution of deep and shallow- water coral reefs is indicated with magenta dots. Coral bleaching 9 From Feely et al 2009 and IPCC AR5-I Life in the Arctic Arctic mammals, such as polar bears, seals and walruses depend on sea ice for habitat, feeding and breeding. They are seriously threatened by sea ice decline. 10 Biodiversity Terrestrial biodiversity tends to be highest near the equator,[2] which seems to be the result of the warm climate and high primary productivity (growth of their biomass ).[3] Marine biodiversity tends to be highest along coasts in the Western Pacific, where sea surface temperature is highest and in the mid-latitudinal band in all oceans.[4 Not the climate itself but rapid climate change has been associated in the past with biodiversity loss. At least 5 large and several smaller mass extinctions have occurred during the last 500 million years, but biodiversity over long time periods has steadily expanded despite these massive losses. Only 1%-3% of the species that have existed on Earth still exist today.[12] At present, biodiversity is declining again but this is already going on from the beginning of the Holocene, more than 10,000 years ago. It is thought to be caused primarily by human impacts, particularly by habitat destruction from human-induced land use change. Thus, biodiversity loss in not an Industial Era event alone, but there are indications that climate change may accelerate loss of biodiversity. However, other factors that are human-related play an even more important role, such as pollution. From 1950 to 2011, human world population increased from 2.5 billion to >7 billion and is predicted to reach a plateau of more than 9 billion during the 21st century.[162] It has been claimed that the massive growth in the human population through the 20th century has had more impact on biodiversity than any other single factor.[163][164] Whatever the causes, biodiversity loss means loss of ‘ecosystem services’ to humans. Biodiversity is a broad subject on its own, it is not further dealt with here but read more here 11 Human health Many deleterious effects of anthropogenic climate change have been reported, such as: Heat-related morbidity and mortality The 2003 summer caused ~15,000 deaths in France. Belgium, the Czech Republic, Germany, Italy, Portugal, Spain, Switzerland, the Netherlands, and the UK all reported excess mortality during the same period, with total deaths in the range of 35,000. In France, deaths were massively reported for people aged 75 and over (60%).