Analysis of Global Change Assessments: Lessons Learned http://www.nap.edu/catalog/11868.html
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ANALYSIS OF GLOBAL CHANGE ASSESSMENTS
integrated assessment in ways that enhance the quality and integrity of the science (Cohen 1997; Kasemir et al. 1999, 2003; Harremoës and Turner 2001; Van Asselt and Rijkens-Klomp 2002; Toth 2003). Not all assessments need to be fully integrated, although there are many benefits to working toward an integrated approach, including a greatly enhanced potential to be policy relevant. In general, an integrated assessment is justified when the problem itself is multidimensional, as is the case with most environmental problems. Having the appropriate disciplines—including both physical, biological, and social scientists—involved in an assessment is critical for both scientific and political credibility. Social scientists are especially critical for structuring the problem and communicating uncertainties and risks (Tol and Vellinga 1998; Van Asselt and Rotmans 2004). For example, climate change can be explained in terms of physical processes that are connected to the wide variety of human activities that give rise to greenhouse gas emissions, leading to impacts on society. Understanding the various links in the chain and their interconnections is an extremely complex undertaking involving inputs from a multitude of disciplines. In addition, social science perspectives can be critical for adequately incorporating uncertainty into models (Van Asselt and Rotmans 2004). The rationale for an integrated assessment is that the separation that differentiates process, impact, and response assessments from each other is ultimately artificial and may lead to science that is less robust than might be ideal. Responses depend on real and perceived impacts; they affect the processes driving global change and consequently alter the impacts; finally, responses themselves have impacts. Rational decision making should take account of the full range of these interactions. Of course, as Levins (1966) has noted, models are always simplifications, so integrated assessments must make decisions about how to simplify. Linked assessments tend to maintain much of the complexity of individual assessments, at the cost of less than full articulation and harmonization. In contrast, fully integrated assessments tend to maximize articulation and harmonization, but at the cost of simplifying. Both of these strategies can be useful, but the trade-offs need to be weighed carefully in advance. For some decisions, the detail contained in linked assessments, but often lost in fully integrated assessments, is essential. However, the limited articulation of linked assessments means that some critical feedbacks are either not considered or considered only qualitatively. Despite the importance of integrated understanding for decision making, methods of integration, whether nested matrices or fully integrated models, are at an early, yet rapid, stage of development (Morgan and Dowlatabadi 1996; Schneider 1997; Tol and Vellinga 1998; Van Asselt and Rotmans 2003; Schneider and Lane 2005) and deserve further development, including model comparisons. The Energy Modeling Forum (http://www.stanford.edu/group/
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