Assessments of climate change impacts, adaptation and vulnerability (CCIAV) are undertaken to inform decision-making in an environment of uncertainty. The demand for such assessments has grown significantly since the release of the IPCC Third Assessment Report (TAR), motivating researchers to expand the ranges of approaches and methods in use, and of the characterisations of future conditions (scenarios and allied products) required by those methods. This chapter describes these developments as well as illustrating the main approaches used to characterise future conditions in the studies reported in this volume.

In previous years, IPCC Working Group II1 has devoted a Special Report and two chapters to assessment methods (IPCC, 1994; Carter et al., 1996; Ahmad et al., 2001). Moreover, the TAR also presented two chapters on the topic of scenarios (Carter et al., 2001; Mearns et al., 2001), which built on earlier descriptions of climate scenario development (IPCC-TGCIA, 1999). These contributions provide detailed descriptions of assessment methods and scenarios, which are not repeated in the current assessment.

In this chapter, an approach is defined as the overall scope and direction of an assessment and can accommodate a variety of different methods. A method is a systematic process of analysis. We identify five approaches to CCIAV in this chapter. Four are conventional research approaches: impact assessment, adaptation assessment, vulnerability assessment, and integrated assessment. The fifth approach, risk management, has emerged as CCIAV studies have begun to be taken up in mainstream policy-making.

Section 2.2 describes developments in the major approaches to CCIAV assessment, followed in Section 2.3 by discussion of a range of new and improved methods that have been applied since the TAR. The critical issue of data needs for assessment is

1 Hereafter, IPCC Working Groups I, II, and III are referred to as WG I, WG II, and WG III, respectively.

treated at the end of this section. Most CCIAV approaches have a scenario component, so recent advances in methods of characterising future conditions are treated in Section 2.4. Since many recent studies evaluated in this volume use scenarios based on the IPCC Special Report on Emissions Scenarios (SRES; Nakicenovic et al., 2000) and derivative studies, boxed examples are presented to illustrate some of these. Finally, in Section 2.5, we summarise the key new findings in the chapter and recommend future research directions required to address major scientific, technical and information deficiencies.

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