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Scientific-Technical Analyses of Impacts, Adaptations, and Mitigation of Climate Change
1. Scope of the Assessment
Box 1. Ultimate Objective of the UNFCCC (Article 2) The charge to Working Group II of the Intergovernmental Panel on Climate Change (IPCC) was to review the state of "...stabilization of greenhouse gas concentrations in the knowledge concerning the impacts of climate change on phys- atmosphere at a level that would prevent dangerous ical and ecological systems, human health, and socioeconomic anthropogenic interference with the climate system. sectors. Working Group II also was charged with reviewing Such a level should be achieved within a time frame available information on the technical and economic feasibili- sufficient to allow ecosystems to adapt naturally to ty of a range of potential adaptation and mitigation strategies. climate change, to ensure that food production is not This assessment provides scientific, technical, and economic threatened, and to enable economic development to information that can be used, inter alia, in evaluating whether proceed in a sustainable manner." the projected range of plausible impacts constitutes “dangerous anthropogenic interference with the climate system." as referred to in Article 2 of the United Nations Framework precipitation, soil moisture, and sea level. Based on the range Convention on Climate Change (UNFCCC), and in evaluat- of sensitivities of climate to increases in greenhouse gas coning adaptation and mitigation options that could be used in centrations reported by IPCC Working Group I and plausible progressing towards the ultimate objective of the UNFCCC ranges of emissions (IPCC IS92; see Table 1), climate models, (see Box 1).
taking into account greenhouse gases and aerosols, project an increase in global mean surface temperature of about 1-3.5°C
by 2100, and an associated increase in sea level of about 15-95 2. Nature of the Issue
cm.' The reliability of regional-scale predictions is still low,
and the degree to which climate variability may change is Human activities are increasing the atmospheric concentrations uncertain. However, potentially serious changes have been of greenhouse gases—which tend to warm the atmosphere— identified, including an increase in some regions in the inciand, in some regions, aerosols—which tend to cool the atmos- dence of extreme high-temperature events, floods, and phere. These changes in greenhouse gases and aerosols, taken droughts, with resultant consequences for fires, pest outbreaks, together, are projected to lead to regional and global changes in and ecosystem composition, structure, and functioning, includclimate and climate-related parameters such as temperature, ing primary productivity.
a Approximate conversion factor: 1 barrel = 6 GJ. Source: IPCC, 1992: Climate Change 1992: The Supplementary Report to the IPCC Scientific Assessment. Section A3, prepared by IPCC Working Group I (J.T. Houghton, B.A. Callander, and S.K. Varncy (eds.)) and WMOUNEP. Cambridge
Scientific-Technical Analyses of Impacts, Adaptations, and Mitigation of Climate Change
Human health, terrestrial and aquatic ecological systems, and Options for adapting to change or mitigating change that can socioeconomic systems (e.g., agriculture, forestry, fisheries, be justified for other reasons today (e.g., abatement of air and water resources) are all vital to human development and and water pollution) and make society more flexible or well-being and are all sensitive to changes in climate. Whereas resilient to anticipated adverse effects of climate change many regions are likely to experience the adverse effects of cli- appear particularly desirable. male change--some of which are potentially irreversible-some effects of climate change are likely to be beneficial. Hence, different segments of society can expect to confront a 3. Vulnerability to Climate Change variety of changes and the need to adapt to them.
Article 2 of the UNFCCC explicitly acknowledges the imporPolicymakers are faced with responding to the risks posed by Lance of natural ecosystems, food production, and sustainable anthropogenic emissions of greenhouse gases in the face of economic development. This report addresses the potential significant scientific uncertainties. It is appropriate to con- sensitivity, adaptability, and vulnerability of ecological and sider these uncertainties in the context of information indi- socioeconomic systems—including hydrology and water cating that climate-induced environmental changes cannot resources management, human infrastructure, and human be reversed quickly, if at all, due to the long time scales health-to changes in climate (see Box 3). associated with the climate system (see Box 2). Decisions taken during the next few years may limit the range of pos- Human-induced climate change adds an important new sible policy options in the future because high near-term stress. Human-induced climate change represents an important emissions would require deeper reductions in the future to additional stress. particularly to the many ecological and meet any given target concentration. Delaying action might socioeconomic systems already affected by pollution, increasreduce the overall costs of mitigation because of potential ing resource demands, and nonsustainable management practechnological advances but could increase both the rate and tices. The most vulnerable systems are those with the greatest the eventual magnitude of climate change, hence the adapla- sensitivity to climate changes and the least adaptability. tion and damage costs.
Most systems are sensitive to climate change. Natural ecoPolicymakers will have to decide to what degree they want logical systems, socioeconomic systems, and human health are to take precautionary measures by mitigating greenhouse gas all sensitive to both the magnitude and the rate of climate emissions and enhancing the resilience of vulnerable sys- change. tems by means of adaptation. Uncertainty does not mean that a nation or the world community cannot position itself belter Impacts are difficult to quantify, and existing studies are lo cope with the broad range of possible climate changes or limited in scope. Although our knowledge has increased sig. protect against potentially costly future outcomes. Delaying nificantly during the last decade, and qualitative estimates can such measures may leave a nation or the world poorly pre- be developed, quantitative projections of the impacts of clipared to deal with adverse changes and may increase the mate change on any particular system at any particular location possibility of irreversible or very costly consequences. are difficult because regional-scale climate change predictions
are uncertain; our current understanding of many critical
processes is limited, and systems are subject to multiple cliBox 2. Time Scales of Processes
matic and non-climatic stresses, the interactions of which are Influencing the Climate System
not always linear or additive. Most impact studies have
assessed how systems would respond to climate change resultTurnover of the capital stock responsible for emis- ing from an arbitrary doubling of equivalent atmospheric carsions of greenhouse gases: Years to decades
bon dioxide (CO) concentrations. Furthermore, very few (without premature retirement)
studies have considered dynamic responses to steadily increasStabilization of almospheric concentrations of long- ing concentrations of greenhouse gases, fewer still have examlived greenhouse gases given a stable level of
ined the consequences of increases beyond a doubling of greenhouse gas emissions: Decades to millennia equivalent atmospheric CO, concentrations or assessed the Equilibration of the climate system given a stable implications of multiple stress factors. level of greenhouse gas concentrations: Decades to centuries
Successful adaptation depends upon technological advances, Equilibration of sea level given a stable climate: institutional arrangements, availability of financing, and Centuries
information exchange. Technological advances generally have Restoration rehabilitation of damaged or disturbed increased adaptation options for managed systems such as agriecological systems. Decades to centuries
culture and water supply. However, many regions of the world (some changes, such as species extinction, are currently have limited access to these technologies and approirreversible, and it may be impossible to recon- priate information. The efficacy and cost-effective use of adapstruct and reestablish some disturbed ecosystems) talion strategies will depend upon the availability of finan.
Scientific-Technical Analyses of Impacts, Adaptations, and Mirigation of Climate Change
Box 3. Sensitivity, Adaptability, and Vulnerability
Sensitivity is the degree to which a system will respond
changes in most ecological and social systems will prove extremely difficult in the coming decades. This is because of the complexity of these systems, their many non-linear feedbacks, and their sensitivity to a large number of climatic and non-climatic factors, all of which are expected to continue to change simultaneously. The development of a baseline projecting future conditions without climate change is crucial. for it is this baseline against which all projected impacts are measured. As future climate extends beyond the boundaries of empirical knowledge (i.e., the documented impacts of climate variation in the past), it becomes more likely that actual outcomes will include surprises and unanticipated rapid changes.
Adaptability refers to the degree to which adjustments
Vulnerability defines the extent to which climate
Further research and monitoring are essential. Enhanced support for research and monitoring, including cooperative efforts from national, international, and multi-lateral institutions, is essential in order to improve significantly regionalscale climate projections; understand the responses of human health, ecological, and socioeconomic systems to changes in climate and other stress factors, and improve our understanding of the efficacy and cost-effectiveness of adaptation strategies.
Both the magnitude and the rate of climate change are
Terrestrial and Aquatic Ecosystems
Ecosystems contain the Earth's entire reservoir of genetic and managerial, institutional, legal, and regulatory practices, both species diversity and provide many goods and services critical domestic and international in scope. Incorporating climate- to individuals and societies. These goods and services include change concerns into resource-use and development decisions (i) providing food, fiber, medicines, and energy: (ii) processing and plans for regularly scheduled investments in infrastructure and storing carbon and other nutrients; (iii) assimilating will facilitate adaptation.
wastes, purifying water, regulating water runoff, and control
ling noods, soil degradation, and beach erosion; and (iv) proVulnerability increases as adaptive capacity decreases. The viding opportunities for recreation and tourism. These systems vulnerability of human health and socioeconomic systems- and the functions they provide are sensitive to the rate and and, to a lesser extent, ecological systems-depends upon eco- extent of changes in climate. Figure 1 illustrates that mean nomic circumstances and institutional infrastructure. This annual temperature and mean annual precipitation can be cor. implies that systems typically are more vulnerable in develop related with the distribution of the world's major biomes. ing countries where economic and institutional circumstances are less favorable. People who live on arid or semi-arid lands, The composition and geographic distribution of many ecosysin low-lying coastal areas, in water-limited or flood-prone tems will shift as individual species respond to changes in cliareas, or on small islands are particularly vulnerable to climate mate; there will likely be reductions in biological diversity and change. Some regions have become more vulnerable to haz- in the goods and services that ecosystems provide society. ards such as storms, floods, and droughts as a result of increas- Some ecological systems may not reach a new equilibrium for ing population density in sensitive areas such as river basins several centuries after the climate achieves a new balance. and coastal plains. Human activities, which fragment many landscapes, have increased the vulnerability of lightly man- Forests. Models project that a sustained increase of l°C in globaged and unmanaged ecosystems. Fragmentation limits natural al mean temperature is sufficient to cause changes in regional adaptation potential and the potential effectiveness of measures climates that will affect the growth and regeneration capacity of to assist adaplation in these systems, such as the provision of forests in many regions. In several instances this will alter the migration corridors. A changing climate's near-term effects on function and composition of forests significantly. As a conseecological and socioeconomic systems most likely will result quence of possible changes in temperature and water availabilifrom changes in the intensity and seasonal and geographic dis- ty under doubled equivalenı-CO, equilibrium conditions, a subtribution of common weather hazards such as storms, noods, stantial fraction (a global average of one-third, varying by region and droughts. In most of these examples, vulnerability can be from one-seventh to two-thirds) of the existing forested area of reduced by strengthening adaptive capacity.
the world will undergo major changes in broad vegetation
types—with the greatest changes occurring in high latitudes and Detection will be difficult, and unexpected changes cannot the least in the tropics Climate change is expected to occur at a be ruled out. Unambiguous detection of climate-induced rapid rate relative to the speed at which forest species grow. increases could be a threat to organisms that exist near their heal-tolerance limits. The impacts on water balance, hydrolo gy, and vegetation are uncertain. Desertification, as defined by
Scientific-Technical Analyses of Impacts, Adaptations, and Mitigation of Climate Change
Mean Annual Temperature (°C)
Deserts and Desertification. Deserts are likely to become 10
more extreme-in that, with few exceptions, they are project
ed to become holter but not significantly wetter. Temperature S
the UN Convention to Combat Desertification, is land degra. -5 BOREAL
dation in arid, semi-arid, and dry sub-humid areas resulting
from various factors, including climatic variations and human Tundra - 10
activities. Desertification is more likely to become irreversible if the environment becomes drier and the soil becomes further degraded through erosion and compaction. Adaptation to
drought and desertification may rely on the development of 500 1000 1500 2000 2500 3000 3500 4000
diversified production systems. Mean Annual Precipitation (mm)
Cryosphere. Models project that between one-third and oneFigure 1: This figure illustrates that mean annual temperature half of existing mountain glacier mass could disappear over the and mean annual precipitation can be correlated with the distribu
nexe 100 years. The reduced extent of glaciers and depth of tion of the world's major biomes. While the role of these annual snow cover also would affect the seasonal distribution of river means in affecting this distribution is important, it should be noted Now and water supply for hydroelectric generation and agriculthai the distribution of biomes may also strongly depend on sea- ture. Anticipated hydrological changes and reductions in the sonal factors such as the length of the dry season or the lowest areal extent and depth of permafrosi could lead to large-scale absolute minimum temperature, on soil properties such as water. damage to infrastructure, an additional flux of Co, into the holding capacity, on land-use history such as agriculture or graz. atmosphere, and changes in processes that contribute to the flux ing, and on disturbance regimes such as the frequency of fire. of methane (CH) into the atmosphere. Reduced sea-ice extent
and thickness would increase the seasonal duration of naviga
tion on rivers and in coastal areas that are presently affected by reproduce, and reestablish themselves. For mid-latitude regions, seasonal ice cover, and may increase navigability in the Arctic a global average warmning of 1-3.5°C over the next 100 years Ocean. Little change in the extent of the Greenland and would be equivalent to a poleward shift of the present isotherms Antarctic ice sheets is expected over the next 50-100 years. by approximately 150-550 km or an altitude shift of about 150–550 m; in low latitudes, temperatures would generally be Mountain Regions. The projected decrease in the extent of increased to higher levels than now exist. This compares to past mountain glaciers, permafrost, and snow cover caused by a tree species migration rates that are believed to be on the order warmer climate will affect hydrologic systems, soil stability, of 4-200 km per century. Therefore, the species composition of and related socioeconomic systems. The altitudinal distribution forests is likely to change; entire forest types may disappear, of vegetation is projected to shift to higher elevation; some while new assemblages of species, hence new ecosystems, may species with climatic ranges limited to mountain tops could be established. Figure 2 depicts potential distribution of biomes become extinct because of disappearance of habitat or reduced under current and a doubled equivalent-CO, climate. Although migration potential. Mountain resources such as food and fuel het primary productivity could increase, the standing biomass of for indigenous populations may be disrupted in many developforesis may not because of more frequent outbreaks and extending countries. Recreational industries of increasing economed ranges of pests and pathogens, and increasing frequency and ic importance to many regions--also are likely to be disrupled. intensity of fires. Large amounts of carbon could be released into the almosphere during transitions from one forest type to anoth- Lakes, Strearns, and Wetlands. Inland aquatic ecosystems e because the rate at which carbon can be lost during times of will be influenced by climate change through altered water high forest monality is greater than the rate at which it can be temperatures, now regimes, and water levels. In lakes and gained through growth to maturity.
streams, warming would have the greatest biological effects at
high latitudes, where biological productivity would increase, Rangelands. In tropical rangelands, mean temperature increas- and at the low-latitude boundaries of cold- and cool-water es should not lead to major alterations in productivity and species ranges, where extinctions would be greatest. Warming