Working Group II has reviewed a huge volume of climate impact assessment studies conducted to date. Most of these studies investigate possible implications of climate change for a single economic sector or environmental component. An increasing, yet still small, fraction of these studies lists options to alleviate impacts, but few take even the next step of exploring direct and indirect costs of those adaptation options. Even fewer studies provide comprehensive assessments of direct and indirect benefits.

Although these studies qualitatively indicate that many policy options proposed as adaptation measures to reduce negative impacts of climate change would be justified even in the absence of climate change (dubbed "no regret" measures on the impacts adaptation side), to date very few have been developed to the point at which comprehensive and quantitative assessment of adaptation options would be possible. Nevertheless, they are a prerequisite for establishing appropriate applications of the more quantitative DAFs reviewed in Section 2.7.2. The main reason is that, despite uncertainties of regional climate change patterns and resulting impacts, some information is generated about possible biophysical impacts. However, little is known about future socioeconomic sensitivity and even less about future adaptive capacity. Resolving this would require fairly detailed regional development scenarios to provide the broader context for sectoral assessments. All these factors together make rigorous applications of quantitative DAFs difficult.

A simple ranking of climate impact and adaptation studies according to how far they get in using DA tools would start with those that are preoccupied almost exclusively with impacts and casually mention some obvious adaptation options. The next category would be studies that attempt to produce a comprehensive list of possible adaptive measures. More advanced studies would explore positive and, if they exist, negative effects of listed options and try to establish at least a qualitative ranking. By assigning monetary values to those comprehensive effects, CBA could help determine the optimal level of adaptation measures; CEA would select the least-cost solution to provide a predetermined level of adaptation objective.

Perhaps the most crucial area of public policy in climate change adaptation is water resource management. A set of papers arranged by Frederick et al. (1997a) looks at different aspects of climate change and water resources planning. Their general conclusion is that DAFs adopted in public policy procedures of water management are largely "appropriate for planning and project evaluation under the prospect of climate change, but new applications and extensions of some criteria may be warranted" (Frederick et al., 1997b). The authors mention nonstationarity, interest rates, and multiple objectives as issues on which progress is required to support better assessments of climate change adaptation decisions.

Water is an important factor to consider in most other sectoral impact and adaptation assessments, even if their primary focus is on a single sector. With a view to the complexity of interactions among sectoral impacts on one hand and adaptation measures on the other, integrated regional assessments increasingly are considered to be indispensable to understand climate-related risks.

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