Emissions Scenarios - IPCC

62 Background and. Overview
effort described in this report. The new set of emissions
scenarios is intended for use in future IPCC assessments and
by wider scientific and policymaliing communities who
analyze the effects of future GHG emissions and develop
mitigation and adaptation measures and policies. The
emissions profiles of tlie new scenarios can provide inputs for
GClVIs and simplified models of climate change. The new
scenarios also contain information, such as the level of
economic activity, rates of technological change and
demographic developments in different world regions, required
to assess climate-change impacts and vulnerabilities,
adaptation strategies and policies. The same kind of
information, in conjunction with emissions trajectories, can
serve as a benchmark for the evaluation of alternative
mitigation measures and policies. Finally, the new set of
scenarios may provide a common basis and an integrative
element for the Third Assessment Report (TAR).
IPCC Working Group III ( WGIII) appointed the SRES writing
team in January 1997. After some adjustments it eventually
included more than 50 scientists. Together they represent a
broad range of scientific disciplines, regional backgrounds and
non-governmental organizations. In particular the team
includes representatives of six leading groups with extensive
expertise in modeling altemative emissions scenarios. It also
includes a number of members who were convening and lead
authors in all three earlier IPCC scenario activities (see above).
Their expertise and familiarity with earlier IPCC emissions
scenario work assured continuity and allowed the SRES effort
to build efficiently upon prior work. Appendix II lists the
members of the writing team and their affiliations.
The writing team reached a consensus concerning the overall
work program. It was agreed that the scenario development
process would consist of four major components.
• First, a review of existing global and regional emissions
scenarios from the published literature and
development of a unique database of 416 global and
regional scenarios (accessible at a web site: wwwcger.nies.go.jp/cger-e/db/ipcc.html).
• Second, an analysis of the range of the scenarios' main
characteristics, their relationships, and their "driving
forces" (such as population, economic development,
energy consumption, rates of technological change and
GHG emissions) and the documentation of the results,
some of which are published in the peer-reviewed
literature.^
• Third, a formulation of narrative "storylines" to
describe the main scenario characteristics, the
development of quantitative prototype scenarios by six
leading groups representing the main modeling
approaches from around the world, and the publication
of the prototype scenarios on a specially developed
IPCC web site (sres.ciesin.org), on web sites of the
modeling teams,'* and in the peer-reviewed literature.^
• Fourth, an "open" process through the IPCC web site
(sres.ciesin.org) that involves feedback from modeling
groups and experts worldwide, followed by the IPCC
expert and govemment reviews that were coordinated
by four review editors.
Most of the background material and findings of the
assessments conducted by the writing team have been
documented in this report and in a series of publications
including two special issues of intemational scientific journals,
Mitigation and Adaptation Strategies for Global Change^ and
Technological Forecasting and Social Change.^
1.2. What are Scenarios?
Scenarios are images of the future, or alternative futures. They
are neither predictions nor forecasts. Rather, each scenario is
one altemative image of how the future might unfold. A set of
scenarios assists in the understanding of possible future
developments of complex systems. Some systems, those that
are well understood and for which complete information is
available, can be modeled with some certainty, as is frequently
the case in the physical sciences, and their future states
predicted. However, many physical and social systems are
poorly understood, and information on the relevant variables is
so incomplete that they can be appreciated only through
intuition and are best communicated by images and stories.
Prediction is not possible in such cases (see Box 1-1 on
uncertainties inherent in scenario analysis).
Scenarios can be viewed as a linking tool that integrates
qualitative narratives or stories about the future and
quantitative formulations based on formal modeling. As such
they enhance our understanding of how systems work, behave
and evolve. Scenarios are useful tools for scientific
assessments, for leaming about complex systems behavior and
for policy making (Jefferson, 1983; Davis, 1999). In scientific
assessments, scenarios are usually based on an internally
consistent and reproducible set of assumptions or theories
about the key relationships and driving forces of change, which
are derived from our understanding of both history and the
current situation. Often scenarios are formulated with the help
of numeric or analytic formal models.
Future levels of global GHG emissions are the products of a
very complex, ill-understood dynamic system, driven by forces
e.g., www-cger.nies.go.jp/cger-e/db/ipcc.html; www.iiasa.ac.at.
3 Anderson, 1998; Alcamo and Swart, 1998; Gaffin, 1998; Gregory,
1998; Gregory and Rogner, 1998; Grübler, 1998; Michaehs, 1998;
Morita and Lee, 1998a; Nakicenovic et al., 1998; Price et al., 1998.
^ de Vries et al., 2000; Fenhann, 2000; Jiang et al., 2000, Jung et ai,
2000; Kram et al., 2000; Mori, 2000; Nakicenovic, 2000; Riahi and
Roehrl, 2000; Roehri and Riahi, 2000; Sankovski et al., 2000.