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SUMMARY FOR POLICYMAKERS: SCIENTIFIC-TECHNICAL ANALYSES OF
IMPACTS, ADAPTATIONS AND MITIGATION OF CLIMATE CHANGE
Most systems are sensitive to climate change. Natural ecological Detection will be difficult and unexpected changes cannot be systems, socio-economic systems and human health are all sensitive ruled out. Unambiguous detection of climate-induced changes in to both the magnitude and the rate of climate change.
most ecological and social systems will prove extremely difficult in
the coming decades. This is because of the complexity of these Impacts are difficult to quantify and existing studies are limited systems, their many non-linear feedbacks, and their sensitivity to a in scope. Although our knowledge has increased significantly during large number of climatic and non-climatic factors, all of which are the last decade, and qualitative estimates can be developed, quanti- expected to continue to change simultaneously. The development tative projections of the impacts of climate change on any particular of a baseline projecting future conditions without climate change is system at any particular location are difficult because regional-scale crucial, for it is this baseline against which all projected impacts are climate change predictions are uncertain; our current understanding measured. As future climate extends beyond the boundaries of of many critical processes is limited; and systems are subject to multi- empirical knowledge (1.e., the documented impacts of climate variple climatic and non-climatic stresses, the interactions of which are ation in the past), it becomes more likely that actual outcomes will not always linear or additive. Most impact studies have assessed how include surprises and unanticipated rapid changes. systems would respond to climate change resulting from an arbitrary doubling of equivalent atmospheric carbon dioxide (CO2) concen- Further research and monitoring are essential. Enhanced support trations. Furthermore, very few studies have considered dynamic for research and monitoring, including cooperative efforts from responses to steadily increasing concentrations of greenhouse gases; national, international and multi-lateral institutions, is essential in fewer still have examined the consequences of increases beyond a order to improve significantly regional-scale climate projections; doubling of equivalent atmospheric CO2 concentrations or assessed understand the responses of human health, ecological and sociothe implications of multiple stress factors.
economic systems to changes in climate and other stress factors;
and improve our understanding of the efficacy and cost-effective Successful adaptation depends upon technological advances, ness of adaptation strategies. institutional arrangements, availability of financing and infor. mation exchange. Technological advances generally have increased adaptation options for managed systems such as agricul- 3.1 Terrestrial and aquatic ecosystems ture and water supply. However, many regions of the world currently have limited access to these technologies and appropriate Ecosystems contain the Earth's entire reservoir of genetic and species information. The efficacy and cost-effective use of adaptation strate- diversity and provide many goods and services critical to individuals gies will depend upon the availability of financial resources, and societies. These goods and services include: (1) providing food, technology transfer, and cultural, educational, managerial, institu- fibre, medicines and energy; (ii) processing and storing carbon and tional, legal and regulatory practices, both domestic and other nutrients; (iii) assimilating wastes, purifying water, regulating international in scope. Incorporating climate change concerns into water runoff, and controlling floods, soil degradation and beach resource-use and development decisions and plans for regularly erosion; and (iv) providing opportunities for recreation and tourism. scheduled investments in infrastructure will facilitate adaptation. These systems and the functions they provide are sensitive to the rate
and extent of changes in climate. Figure 1 illustrates that mean Vulnerability increases as adaptive capacity decreases. The vulner- annual temperature and mean annual precipitation can be correlated ability of human health and socio-economic systems-and, to a lesser with the distribution of the world's major biomes. extent, ecological systems - depends upon economic circumstances and institutional infrastructure. This implies that systems typically are The composition and geographic distribution of many ecosystems more vulnerable in developing countries where economic and insti. will shift as individual species respond to changes in climate; there tutional circumstances are less favourable. People who live on arid or will likely be reductions in biological diversity and in the goods and semi-arid lands, in low-lying coastal areas, in water-limited or flood- services that ecosystems provide society. Some ecological systems prone areas, or on small islands are particularly vulnerable to climate may not reach a new equilibrium for several centuries after the change. Some regions have become more vulnerable to hazards such climate achieves a new balance. as storms, noods and droughts as a result of increasing population density in sensitive areas such as river basins and coastal plains. Human Forests. Models project that a sustained increase of 1°C in global activities, which fragment many landscapes, have increased the mean temperature is sufficient to cause changes in regional climates vulnerability of lightly managed and unmanaged ecosystems. that will affect the growth and regeneration capacity of forests in Fragmentation limits natural adaptation potential and the potential many regions. In several instances this will alter the function and effectiveness of measures to assist adaptation in these systems, such as composition of forests significantly. As a consequence of possible the provision of migration corridors. A changing climate's near-term changes in temperature and water availability under doubled effects on ecological and socio-economic systems most likely will result equivalent-CO2 equilibrium conditions, a substantial fraction (a from changes in the intensity and seasonal and geographic distribution global average of one-third, varying by region from one-seventh to of common weather hazards such as storms, floods and droughts. In two-thirds) of the existing forested area of the world will undergo most of these examples, vulnerability can be reduced by strengthen- major changes in broad vegetation types – with the greatest ing adaptive capacity.
changes occurring in high latitudes and the least in the tropics. CLIMATE CHANGE 1995: IPCC SECOND ASSESSMENT REPORT
Climate change is expected to occur at a rapid rate relative to the Rangelands. In tropical rangelands, mean temperature increases should speed at which forest species grow, reproduce and re-establish not lead to major alterations in productivity and species composition, themselves. For mid-latitude regions, a global average warming of but altered rainfall amount and seasonality and increased evapotran 1-3.5°C over the next 100 years would be equivalent to a poleward spiration will. Increases in atmospheric CO2 concentration may raise shift of the present isotherms by approximately 150-550 km or an the carbon-to-nitrogen ratio of forage for herbivores, thus reducing its altitude shift of about 150-550 m; in low latitudes, temperatures food value. Shifts in temperature and precipitation in temperate range would generally be increased to higher levels than now exist. This lands may result in altered growing seasons and boundary shifts compares to past tree species migration rates that are believed to be between grasslands, forests and shrublands. on the order of 4-200 km per century. Therefore, the species composition of forests is likely to change; entire forest types may Deserts and desertification. Deserts are likely to become more disappear, while new assemblages of species, hence new ecosystems, extreme – in that, with few exceptions, they are projected to may be established. Figure 2 depicts potential distribution of biomes become hotter but not significantly wetter. Temperature increases under current and a doubled equivalent-CO2 climate. Although net could be a threat to organisms that exist near their heat-tolerance primary productivity could increase, the standing biomass of forests limits. The impacts on water balance, hydrology and vegetation are may not because of more frequent outbreaks and extended ranges of uncertain. Desertification, as defined by the UN Convention to pests and pathogens, and increasing frequency and intensity of Combat Desertification, is land degradation in arid, semi-arid and fires. Large amounts of carbon could be released into the dry sub-humid areas resulting from various factors, including atmosphere during transitions from one forest type to another climatic variations and human activities. Desertification is more because the rate at which carbon can be lost during times of high likely to become irreversible if the environment becomes drier and forest mortality is greater than the rate at which it can be gained the soil becomes further degraded through erosion and compaction. through growth to maturity.
Adaptation to drought and desertification may rely on the develop ment of diversified production systems.
Cryosphere. Models project that between one-third and one-half of existing mountain glacier mass could disappear over the next 100 years. The reduced extent of glaciers and depth of snow cover also would affect the seasonal distribution of river flow and water supply for hydroelectric generation and agriculture. Anticipated hydrological changes and reductions in the areal extent and depth of permafrost could lead to large-scale damage to infrastructure, an additional flux of CO2 into the atmosphere and changes in processes that contribute to the flux of methane (CH.) into the atmosphere. Reduced sea-ice extent and thickness would increase the seasonal duration of navigation on rivers and in coastal areas that are presently affected by seasonal ice cover and may increase navigability in the Arctic Ocean. Little change in the extent of the Greenland and Antarctic ice sheets is expected over the next 50-100 years.
Mean Annual Temperature (°C)
Mountain regions. The projected decrease in the extent of BOREAL
mountain glaciers, permafrost and snow cover caused by a Tundra
warmer climate will affect hydrologic systems, soil stability and -10
related socio-economic systems. The altitudinal distribution of
vegetation is projected to shift to higher elevation; some species 500 1000 1500 2000 2500 3000 3500 4000
with climatic ranges limited to mountain tops could become Mean Annual Precipitation (mm)
extinct because of disappearance of habitat or reduced migration potential. Mountain resources such as food and fuel for indigenous
populations may be disrupted in many developing countries. Figure 1. This figure illustrates that mean annual temperature and Recreational industries — of increasing economic importance to mean annual precipitation can be correlated with the distribution many regions – also are likely to be disrupted. of the world's major biomes. While the role of these annual means in affecting this distribution is important, it should be noted that Lakes, streams and wetlands. Inland aquatic ecosystems will be the distribution of biomes may also strongly depend on seasonal influenced by climate change through altered water temperatures, factors such as the length of the dry season or the lowest absolute flow regimes and water levels. In lakes and streams, warming would minimum temperature, on soil properties such as water-holding have the greatest biological effects at high latitudes, where biologi capacity, on land-use history such as agriculture or grazing and on cal productivity would increase, and at the low-latitude boundaries disturbance regimes such as the frequency of fire.
of cold- and cool-water species ranges, where extinctions would be
Figure 2. Potential distribution of the major world biomes under current climate conditions, simulated by Mapped Atmosphere-Plant-Soil System (MAPSS) model (top). "Potential distribution" indicates the natural vegetation that can be supported at each site, given monthly inputs of precipitation, temperature, humidity and windspeed. The lower product illustrates the projected distribution of the major world biomes by simulating the effects of 2 x CO2-equivalent concentrations (GFDL general circulation model), including the direct physiological effects of CO2 on vegetation. Both products are adapted from: Neilson, R.P. and D. Marks, 1994: A global perspective of regional vegetation and hydrologic sensitivities from climate change. Journal of Vegetation Science, 5, 715-730.
greatest. Warming of larger and deeper temperate zone lakes would level declines will be most severe in lakes and streams in dry evapincrease their productivity; although in some shallow lakes and in orative drainages and in basins with small catchments. The streams, warming could increase the likelihood of anoxic condi- geographical distribution of wetlands is likely to shift with changes tions. Increases in slow variability, particularly the frequency and in temperature and precipitation. There will be an impact of climate duration of large floods and droughts, would tend to reduce water change on greenhouse gas release from non-tidal wetlands, but quality and biological productivity and habitat in streams. Water- there is uncertainty regarding the exact effects from site to site.
CLIMATE CHANGE 1995: II'CC SECOND ASSESSMENT REPORT
Coastal systems. Coastal systems are economically and ecologically The quantity and quality of water supplies already are serious important and are expected to vary widely in their response to problems today in many regions, including some low-lying coastal changes in climate and sea level. Climate change and a rise in sea areas, deltas and small islands, making countries in these regions level or changes in storms or storm surges could result in the erosion particularly vulnerable to any additional reduction in Indigenous of shores and associated habitat, increased salinity of estuaries and water supplies. Water availability currently falls below 1,000 m3 per freshwater aquifers, altered tidal ranges in rivers and bays, changes in person per year -- a common benchmark for water scarcity – in a sediment and nutrient transport, a change in the pattern of chemi- number of countries (e.g., Kuwait, Jordan, Israel, Rwanda, Somalia, cal and microbiological contamination in coastal areas, and increased Algeria, Kenya) or is expected to fall below this benchmark in the coastal flooding. Some coastal ecosystems are particularly at risk, next two to three decades (e.g., Libya, Egypt, South Africa, Iran, including saltwater marshes, mangrove ecosystems, coastal wetlands, Ethiopia). In addition, a number of countries in conflict-prone areas coral reefs, coral atolls and river deltas. Changes in these ecosystems are highly dependent on water originating outside their borders would have major negative effects on tourism, freshwater supplies, (e.g., Cambodia, Syria, Sudan, Egypt, Iraq). fisheries and biodiversity. Such impacts would add to modifications in the functioning of coastal oceans and inland waters that already The impacts of climate change will depend on the baseline have resulted from pollution, physical modification and material condition of the water supply system and the ability of water inputs due to human activities.
resource managers to respond not only to climate change but also to
population growth and changes in demands, technology, and Oceans. Climate change will lead to changes in sea level, increasing economic, social and legislative conditions. In some cases it on average, and also could lead to altered ocean circulation, particularly in wealthier countries with integrated watervertical mixing, wave climate and reductions in sea-ice cover. As a management systems — improved management may protect water result, nutrient availability, biological productivity, the structure users from climate change at minimal cost; in many others, and functions of marine ecosystems, and heat and carbon storage however, there could be substantial economic, social and capacity may be affected, with important feedbacks to the climate environmental costs, particularly in regions that already are watersystem. These changes would have implications for coastal regions, limited and where there is considerable competition among users. fisheries, tourism and recreation, transport, off-shore structures and Experts disagree over whether water supply systems will evolve communication. Paleoclimatic data and model experiments suggest substantially enough in the future to compensate for the that abrupt climatic changes can occur if freshwater influx from the anticipated negative impacts of climate change on water resources movement and melting of sea ice or ice sheets significantly weakens and for potential increases in demand, global thermohaline circulation.
Options for dealing with the possible impacts of a changed climate 3.2 Hydrology and water resources management
and increased uncertainty about future supply and demand for
freshwater include more efficient management of existing supplies Climate change will lead to an intensification of the global and infrastructure; institutional arrangements to limit future hydrological cycle and can have major impacts on regional water demands/promote conservation; improved monitoring and resources. A change in the volume and distribution of water will forecasting systems for floods/droughts; rehabilitation of affect both ground and surface water supply for domestic and watersheds, especially in the tropics; and construction of new industrial uses, irrigation, hydropower generation, navigation, reservoir capacity to capture and store excess flows produced by instream ecosystems and water-based recreation.
altered patterns of snowmelt and storms.
Changes in the total amount of precipitation and in its frequency 3.3 Food and fibre and intensity directly affect the magnitude and timing of runoff and the intensity of floods and droughts; however, at present, Agriculture. Crop yields and changes in productivity due to climate specific regional effects are uncertain. Relatively small changes in change will vary considerably across regions and among localities, temperature and precipitation, together with the non-linear thus changing the patterns of production. Productivity is projected to effects on evapotranspiration and soil moisture, can result in increase in some areas and decrease in others, especially the tropics relatively large changes in runoff, especially in arid and semi-arid and subtropics (Table 2). However, existing studies show that on the regions. High-latitude regions may experience increased runoff due whole global agricultural production could be maintained relative to to increased precipitation, whereas runoff may decrease at lower baseline production in the face of climate change modeled by general latitudes due to the combined effects of increased circulation models (GCMs) at doubled equivalent-CO2 equilibrium evapotranspiration and decreased precipitation. More intense conditions, but that regional effects would vary widely. This conclu. rainfall would tend to increase runoff and the risk of flooding, sion takes into account the beneficial effects of CO2 fertilization, but although this would depend not only on the change in rainfall but does not allow for changes in agricultural pests and the possible also on catchment physical and biological characteristics. A effects of changing climatic variability. warmer climate could decrease the proportion of precipitation falling as snow, leading to reductions in spring runoff and Focusing on global agricultural production does not address the increases in winter runoff.
potentially serious consequences of large differences at local and SUMMARY FOR I'OLICYMAKERS: SCIENTIFIC-TECHNICAL ANALYSES OF
IMPACTS, ADAPTATIONS AND MITIGATION OF CLIMATE CHANGE
Table 2. Selected crop study results for 2 x CO equivalent equilibrium GCM scenarios.
Data are from France, Spain and northern Europe; with adaptation and
Data are from Egypt, Kenya, South Africa and Zimbabwe; range is over
Data are from Bangladesh, India, Philippines, Thailand, Indonesia,
Data are from Japan and South Korea; range is across GCM
15 to +30
Other Asia and
-1 to 35
41 to +65
Note: For most regions, studies have focused on one or two principal grains. These studies strongly demonstrate the variability in estimated yield impacts among countries, scenarios, methods of analysis and crops, making it difficult to generalize results across areas or for different dimate scenarios.
regional scales, even at mid-latitudes. There may be increased risk of southeast Asia; and tropical areas of Latin America, as well as some hunger and famine in some locations; mmy of the world's poorest Pacific island nations. people — particularly those living in subtropical and tropical areas and dependent on isolated agricultural systems in semi-arid and Adaptation - such as changes in crops and crop varieties, improved arid regions — are most at risk of increased hunger. Many of these water-management and irrigation systems, and changes in planting at-risk populations are found in sub-Saharan Africa; south, east and schedules and tillage practices – will be important in limiting