2.1 Introduction: Summary of the Second Assessment Report and Progress since
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
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