Why new Intergovernmental Panel on Climate Change scenarios?
The Intergovernmental Panel on Climate Change (IPCC) developed long-term
emission scenarios in 1990 and 1992. These scenarios have been widely used
in the analysis of possible climate change, its impacts, and options to mitigate
climate change. In 1995, the IPCC 1992 scenarios were evaluated. The evaluation
recommended that significant changes (since 1992) in the understanding of driving
forces of emissions and methodologies should be addressed. These changes in
understanding relate to, e.g., the carbon intensity of energy supply, the income
gap between developed and developing countries, and to sulfur emissions. This
led to a decision by the IPCC Plenary in 1996 to develop a new set of scenarios.
The new set of scenarios is presented in this report.
What are scenarios and what is their purpose?
Future greenhouse gas (GHG) emissions are the product of very complex dynamic
systems, determined by driving forces such as demographic development, socio-economic
development, and technological change. Their future evolution is highly
uncertain. Scenarios are alternative images of how the future might unfold and
are an appropriate tool with which to analyze how driving forces may influence
future emission outcomes and to assess the associated uncertainties. They assist
in climate change analysis, including climate modeling and the assessment of
impacts, adaptation, and mitigation. The possibility that any single emissions
path will occur as described in scenarios is highly uncertain.
What are the main characteristics of the new scenarios?
A set of scenarios was developed to represent the range of driving forces
and emissions in the scenario literature so as to reflect current understanding
and knowledge about underlying uncertainties. They exclude only outlying
"surprise" or "disaster" scenarios in the literature. Any scenario necessarily
includes subjective elements and is open to various interpretations. Preferences
for the scenarios presented here vary among users. No judgment is offered in
this report as to the preference for any of the scenarios and they are not assigned
probabilities of occurrence, neither must they be interpreted as policy recommendations.
The scenarios are based on an extensive assessment of driving forces and
emissions in the scenario literature, alternative modeling approaches, and an
that solicited wide participation and feedback. These are all-important
elements of the Terms of Reference (see Appendix I).
Four different narrative storylines were developed to describe consistently
the relationships between emission driving forces and their evolution and add
context for the scenario quantification. Each storyline represents different
demographic, social, economic, technological, and environmental developments,
which may be viewed positively by some people and negatively by others.
The scenarios cover a wide range of the main demographic, economic, and
technological driving forces of GHG and sulphur emissions 2
and are representative of the literature. Each scenario represents a specific
quantitative interpretation of one of four storylines. All the scenarios based
on the same storyline constitute a scenario "family".
As required by the Terms of Reference, the scenarios in this report do not
include additional climate initiatives, which means that no scenarios are included
that explicitly assume implementation of the United Nations Framework Convention
for Climate Change (UNFCCC) or the emissions targets of the Kyoto Protocol.
However, GHG emissions are directly affected by non-climate change policies
designed for a wide range of other purposes. Furthermore government policies
can, to varying degrees, influence the GHG emission drivers such as demographic
change, social and economic development, technological change, resource use,
and pollution management. This influence is broadly reflected in the storylines
and resultant scenarios.
For each storyline several different scenarios were developed using different
modeling approaches to examine the range of outcomes arising from a range of
models that use similar assumptions about driving forces. Six models were
used which are representative of integrated assessment frameworks in the literature.
One advantage of a multi-model approach is that the resultant 40 SRES scenarios
together encompass the current range of uncertainties of future GHG emissions
arising from different characteristics of these models, in addition to the current
knowledge of and uncertainties that arise from scenario driving forces such
as demographic, social and economic, and broad technological developments that
drive the models, as described in the storylines. Thirteen of these 40 scenarios
explore variations in energy technology assumptions.