Various options for mitigating climate change, which constitute the basis of this Working Group III report, depend on societal visions of the future. These visions largely define the decision analytical frameworks used (see Chapter 10) and form the basis for evaluating options. As this chapter will make clear, existing visions of the future are very different in scope and scale, in time horizons, in constituents and uncertainties, and cover different areas of human activities, natural conditions, etc. Whereas some authors explore the future by extrapolating trends, others aim at a more desirable future state.

Many visions of the future can be modified into scenarios through the systematization of data and other available information, using various modelling techniques, and thereby leading to quantitative interpretations of the future. The spectrum of scenarios can be as broad as that of visions, however, articulating a scenario can provide a more detailed picture of the framework for decisions and the associated limitations for decision-making processes and policy interventions in any particular area.

Climate change and its impacts have a long history in the existing scenario literature, while mitigation scenarios that explore policy options to be implemented are of more recent origin. In the Second Assessment Report (SAR) of the Intergovernmental Panel on Climate Change (IPCC), greenhouse gas (GHG) mitigation scenarios were reviewed. Since that time, there has been considerable development of such scenarios, focussing on issues of the timing, location, and extent of responses required to stabilize atmospheric concentrations at various levels. These new mitigation scenarios are reviewed in this chapter.

Another literature, consisting of more narrative-based scenarios of alternative global futures, is also reviewed in this chapter. These more general scenarios provide a basis for contextualizing the more traditional emissions scenarios, and providing a link to development, equity, and sustainability (DES).

In addition, in 1996, the IPCC commissioned a new report on emissions scenarios (the Special Report on Emissions Scenarios, or SRES), in which new scenarios were developed (Nakicenovic et al., 2000). During 1999 and 2000 various modellers used these new reference scenarios as the basis of new mitigation and stabilization analyses. This post-SRES work is also reviewed in this chapter.

Section 2.2 provides a background of scenarios in general, and emission and mitigation scenarios in particular, and discusses the link between scenarios and DES. Section 2.3 reviews general mitigation scenarios produced since the SAR. Section 2.4 discusses global futures scenarios, which are narrative-based scenarios found in the general futures literature. Section 2.5 provides a review of the SRES and discusses post-SRES mitigation scenarios. Finally, Section 2.6 provides recommendations for future research.

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