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IPCC Working Group I 1995 Summary for Policymakers

some of the effects of aerosols suggest that monsoon precipitation may decrease. The spatial and temporal distribution of aerosols greatly influence regional projections, which

are therefore more uncertain. • A general warming is expected to lead to an increase in the occurrence of extremely hot

days and a decrease in the occurrence of extremely cold days. • Warmer temperatures will lead to a more vigorous hydrological cycle; this translates into

prospects for more severe droughts and/or floods in some places and less severe droughts and/or floods in other places. Several models indicate an increase in precipitation intensity, suggesting a possibility for more extreme rainfall events. Knowledge is currently insufficient to say whether there will be any changes in the occurrence or geographical distribution of severe storms, e.g., tropical cyclones. Sustained rapid climate change could shift the competitive balance among species and even lead to forest dieback, altering the terrestrial uptake and release of carbon. The magnitude is uncertain, but could be between zero and 200 GtC over the next one to two centuries, depending on the rate of climate change.

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There are still many uncertainties

Many factors currently limit our ability to project and detect future climate change. In particular, to reduce uncertainties further work is needed on the following priority topics: • estimation of future emissions and biogeochemical cycling (including sources and sinks) of

greenhouse gases, aerosols and aerosol precursors and projections of future

concentrations and radiative properties. • representation of climate processes in models, especially feedbacks associated with clouds,

oceans, sea ice and vegetation, in order to improve projections of rates and regional
patterns of climate change.
systematic collection of long-term instrumental and proxy observations of climate system
variables (e.g., solar output, atmospheric energy balance components, hydrological
cycles, ocean characteristics and ecosystem changes) for the purposes of model testing,
assessment of temporal and regional variability and for detection and attribution studies.

Future unexpected, large and rapid climate system changes (as have occurred in the past) are,
by their nature difficult to predict. This implies that future climate changes may also involve
"surprises". In particular these arise from the non-linear nature of the climate system.
When rapidly forced, non-linear systems are especially subject to unexpected behaviour.
Progress can be made by investigating non-linear processes and sub-components of the
climatic system. Examples of such non-linear behaviour include rapid circulation changes in
the North Atlantic and feedbacks associated with terrestrial ecosystem changes.

Summary for Policymakers:

Scientific-Technical Analyses of Impacts, Adaptations, and Mitigation of Climate Change

A Report of Working Group II
of the Intergovernmental Panel on Climate Change

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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.

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*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 1 (J.T. Houghton, B.A. Callander, and S.K. Varney (eds.)) and WMONUNEP. 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 adapta- 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 better Impacts are difficult to quantify, and existing studies are to cope with the broad range of possible climate changes or limited in scope. Although our knowledge has increased sigprotect against potentially costly fulure 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 atmospheric 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, avaiability 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) tation strategies will depend upon the availability of finan

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