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nomic, cultural, and other factors that are essential for understanding the potential to reduce emissions and adapt to changed climate conditions. These factors are currently underrepresented in integrated assessment models of emissions and consequences of climate change and mitigation policies.

Scenarios

Scenarios are tools for analyzing situations in which outcomes are uncertain. The goal of working with scenarios is not to predict the future but to better understand uncertainties in order to reach decisions that are robust under a wide range of possible futures. Space constraints do not allow a full review of scenario development, but such reviews exist in the literature.102

In climate change research, scenarios describe plausible trajectories of different aspects of the future that are constructed to investigate the potential consequences of anthropogenic climate change. Over time, an increasingly broad array of scenarios has been developed to address different components of the issue. Scenarios currently represent major driving forces, processes, impacts, and potential responses important for informing climate change policy. See Box C.1 for a detailed description of types of scenarios used in climate change research.

A variety of techniques have been used in developing scenarios. For climate scenarios, these approaches include analogues of anticipated future conditions (both temporal and spatial), and model-based scenarios produced with general circulation models (GCMs—both global and regional) “forced” with scenarios of emissions.103 Emissions scenarios are developed primarily using integrated assessment models (IAMs), which are comprehensive representations of quantifiable socioeconomic (e.g., demographic, economic, and technological) and environmental (e.g., land use) drivers of emissions and, increasingly, impacts. 104 A variety of environmental scenarios (e.g., sea level rise, hydrology, land cover, air quality) are produced with specialized hydrological, agricultural, ecological, and other models that incorporate both human and environmental processes—these, along with climate scenarios and socioeconomic assumptions are commonly used in evaluating potential consequences of climate change for a variety of human and natural systems. 105 Quantitative approaches to scenarios do not adequately account for political, cultural, and institutional influences that are important in understanding innovation, technological change, and the ability of societies to effectively implement policies. These factors are most often represented in qualitative narratives or storylines, which are used by analysts in a variety of ways to coordinate scenarios across scales or subject matters.106,107

Many different groups have used scenarios at different spatial scales. At a global scale, the IPCC has used emissions and climate scenarios as a central component of its work of assessing climate change research. The IPCC has commissioned several sets of emissions scenarios for use in its reports, convening authors and modelers, providing terms of reference, and approving the scenarios through an intergovernmental process that took several

102

Parson, E.A. et al. Global Change Scenarios: Their Development and Use (Sub-report 2.1B of Synthesis and Assessment Product 2.1, U.S. Climate Change Science Program and the Subcommittee on Global Change Research, Department of Energy, Office of Biological and Environmental Research, Washington DC (2007).

103

Mearns, L.O. et al. Climate Scenario Development. In Climate Change 2001: The Physical Science Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change, eds J.T. Houghton, Y. Ding, and D.J. Griggs. Cambridge University Press, Cambridge, UK. 739-768 (2001).

104

For an excellent review of emissions scenario methods and literature, see Nakicenovic, N., et al. Special Report on Emissions Scenarios: A Special Report of Working Group III of the Intergovernmental Panel on Climate Change (Cambridge Univ. Press, 2000).

105

For an overview of the use of different types of scenarios in assessment of impacts, adaptation, and vulnerability, see Carter, T.R. et al. Developing and Applying Scenarios. In Climate Change 2001: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Third Assessment Report of the Intergovernmental Panel on Climate Change Eds J.J. McCarthy, O.F. Canziani, N.A. Leary, D.J. Dokken, and K.S. White. Cambridge University Press, Cambridge, UK. 145-190 (2001).

106

National Research Council. Describing Socioeconomic Futures for Climate Change Research and Assessment: Report of a Workshop. Panel on Socio-Economic Scenarios for Climate Change Research and Assessment, Committee on the Human Dimensions of Global Change, Division of Behavioral and Social Science and Education. Washington, DC: The National Academies Press (2010).

107

Arnell, N.W. et al. Climate and socio-economic scenarios for global-scale climate change impacts assessments: Characterising the SRES storylines. Global Environmental Change 14, 3-20 (2004).



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