ACACIA (A Concerted Action Towards A Comprehensive Climate Impacts and Adaptations Assessment for the European Union) assessed climate impacts and potential adaptation in Europe to the 2080s (Parry, 2000). ACACIA elaborated four scenarios on the basis of a combination of the UKCIP and SRES approaches (Jordan et al., 2000; see also Chapter 13). This analysis concluded that certain systems will thrive under some scenarios and will be inherently more vulnerable in others, independent of climate change. Adaptive strategies are likely to differ across the four scenarios. In addition, the manner in which society values different parts of the human and physical environment is markedly different under the different scenarios, with clear implications for adaptation policies.
The approach to socioeconomic scenarios adopted by the U.S. National Assessment of Climate Impacts was determined by the nature of the assessment process, with a national synthesis linking separate analyses in nine U.S. regions and five sectors (National Assessment Synthesis Team, 1998). Recognizing that the sensitivity of particular regions or sectors may depend on highly specific socioeconomic characteristics, the assessment adopted a two-part approach to scenario development. First, to allow national aggregation, high, medium, and low scenarios were specified for variables such as population and GDP to be used by all subnational analyses (NPA Data Services, 1999). Second, teams were asked to identify a small number of additional socioeconomic variables that would have the strongest and most direct influence on their particular region or sector. They developed and documented their own assumptions for these variables, following a consistent template developed by the National Assessment Synthesis Team (NAST) (Parson, 1999). High and low values then could be assumed for each key impact variable, without having to specify what combination of demographic, market, ecosystem, and technological factors caused it to take a particular value. Teams were advised to construct a small set of high- and low-impact scenarios on the basis of different combinations of assumptions about key impact variables. Instead of an idealized approach to scenario development, which would have attempted to specify all factors consistently across different sectors and regions, the more pragmatic and pluralistic approach adopted in the U.S. National Assessment allowed regional and sectoral specificities to be reflected.
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