An important new category of issues on climatic impacts pertains to methodological advances; Chapter 2 provides more details. These advances include methods for assessing impacts and vulnerability, methods for detecting biotic response to climate change in natural ecological systems by using indicator species, and detection and attribution of observed changes in environmental systems to climatic changes, as distinct from other possible causal factors (Chapter 5). Other new methods relate to costing and valuation, decision analytic techniques and frameworks, uncertainties assessment, and consistent characterization of levels of confidence that could be attached to observations or conclusions (see Box 1-2 and Chapter 2). All of these developments extend methodological considerations beyond those typically employed in the SAR. Development and application of regional-scale scenarios to climate change impacts, adaptations, and vulnerability (as described in Chapter 3) represent a new emphasis of a technique that was limited in the SAR to the science of climate change. The directive in the IPCC’s charge to Working Group II to emphasize regional issues is reflected in the eight regional chapters (Chapters 10–17). This directive calls for utilization of new advances in knowledge, including integrated methods, to assess the most cost-effective approaches to adapt to changes in climate at the regional level. This section elaborates briefly on several issues that are related to assessment of impacts, vulnerability, and adaptation and illustrates several of the foregoing methodological considerations.

Figure 1-2: Places of adapatation in the climate change issue (Smit et al., 1999).

This report assesses recent advances in our understanding of the vulnerability of major sectors, systems, and regions to climate change. Consistent with common usage and definitions in the SAR, vulnerability is defined as the extent to which a natural or social system is susceptible to sustaining damage from climate change. Vulnerability is a function of the sensitivity of a system to changes in climate (the degree to which a system will respond to a given change in climate, including beneficial and harmful effects), adaptive capacity (the degree to which adjustments in practices, processes, or structures can moderate or offset the potential for damage or take advantage of opportunities created by a given change in climate), and the degree of exposure of the system to climatic hazards (Figure 1-2). Under this framework, a highly vulnerable system would be a system that is very sensitive to modest changes in climate, where the sensitivity includes the potential for substantial harmful effects, and for which the ability to adapt is severely constrained. Resilience is the flip side of vulnerability—a resilient system or population is not sensitive to climate variability and change and has the capacity to adapt.

Adaptation is recognized as a crucial response because even if current agreements to limit emissions are implemented, they will not stabilize atmospheric concentrations of GHG emissions and climate (Wigley, 1998). Hence, adaptation is considered here, along with mitigation—the more widely considered response to climate change—as a key component of an integrated and balanced response to climate variability and change (MacIver, 1998). Adaptations, which can be autonomous or policy-driven, are adjustments in practices, processes, or structures to take account of changing climate conditions. Impacts, however, sometimes are difficult to identify, let alone quantify, in part because of the nonlinear nature of climate change itself. Impacts can be subtle but nonetheless significant, and their consequences can differ for different members of the same community—as when some individuals or groups perceive an opportunity with change and others experience a loss, thereby changing community dynamics and complicating decisions about how to adapt and the apportionment of costs of adaptation. Negative impacts often are observed as chance occurrences (surprises) beyond critical values (thresholds) of accustomed weather parameters. They can be conceived as risks or the “probability of occurrence of a damaging event,” such as flood, drought, strong winds, heat wave, subfreezing temperatures, or forest or bush fire. “The extent to which natural ecosystems, global food supplies and sustainable development are in danger depends partly on the nature of climate change and partly on the ability of the impacted systems to adapt” to these events (Smit et al., 1999).

The capacity of a sector or region to adapt to climatic changes depends on several factors (see Figure 1-2 and Chapter 18). The literature emphasizes that studies that neglect adaptive potential are likely to overestimate the costs of climatic impacts (e.g., Reilly et al., 1996). However, more recent literature also notes that maladaptations are possible—particularly when information about future climatic and other conditions is much less than perfect—as a response to an incorrect perception of such changes, often driven by a masking of slowly evolving trends by large natural variability or extreme events (West and Dowlatabadi, 1999; Schneider et al., 2000a; West et al., 2001). Maladaptations can increase the costs of impacts relative to those when adaptive agents have perfect foresight or when adaptive responses are absent. On the other hand, appropriate adaptations can reduce negative impacts or take advantage of new opportunities presented by changing climate conditions. The SAR assessed technical options for adaptation but did not evaluate the feasibility of these options for different regions and circumstances because little information was available in the literature. The Special Report on Regional Impacts of Climate Change focuses to a greater extent on the regional dimensions of adaptation; because the report is based largely on the SAR, as well as early and preliminary results from country studies and national communications to the UNFCCC, however, many questions about the capacities required to implement theoretically promising adaptation options remain. Hence, in this report, greater attention has been focused on societal determinants of adaptive capacity and vulnerability. To the extent possible, the report seeks to examine information in the literature on the interaction of these factors to develop options for bolstering adaptive capacity. Previous IPCC assessments conclude that most systems are sensitive to the magnitude and the rate of climate change. Sensitive systems include, for example, aspects of food and fiber production, water resources, ecosystems of all types, coastal systems, human settlements, and human health. This sensitivity includes adverse effects in many regions, as well as potentially beneficial effects in some regions and sectors (high confidence). Social systems generally are more resilient than natural systems because of the potential for deliberate adaptation (high confidence). However, confidence in most specific aggregate estimates of impacts remains low because of uncertainties and complexities of analysis (as detailed further in succeeding sections).

For systems that already are exposed to increasing resource demands, unsustainable management, and pollution, exposure to climate change is an important additional pressure. Systems that are exposed to multiple pressures (synergistic effects) usually are more vulnerable to climate change than systems that are not (high confidence).

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