Emissions Scenarios - IPCC

296 Summary Discussions and Recommendations
Box 6-1: The Main Characteristics of the Four SRES Storylines and Scenario Families.
By 2100 the world will have changed in ways that are hard to imagine - as hard as it would have been at the end of the 19th
century to imagine the changes of the 100 years since. Each storyline assumes a distinctly different direction for future
developments, such that the four storylines differ in increasingly irreversible ways. Together they describe divergent futures that
encompass a significant portion of the underlying uncertamties in the main driving forces. They cover a wide range of key
"future" characteristics such as population growth, economic development, and technological change. For this reason, their
plausibility or feasibiUty should not be considered solely on the basis of an extrapolation of current economic, technological,
and social trends.
• The Al storylme and scenario family describes a future world of very rapid economic growth, low population growth, and
the rapid introduction of new and more efficient technologies. Major underlymg themes are convergence among regions,
capacity buildmg and increased cultural and social interactions, with a substantial reduction in regional differences in per
capita income. The Al scenario family develops into four groups that describe altemative dnections of technological
change in the energy system. Please note that m the Summary for Policymakers, two of these groups were merged into
one?
• The A2 storyline and scenario family describes a very heterogeneous world. The underlying theme is self-reliance and
preservation of local identities. Fertility pattems across regions converge very slowly, which results in high population
growth. Economic development is primarily regionally oriented and per capita econontic growth and technological change
are more fragmented and slower than in other storylines.
• The Bl storyline and scenario family describes a convergent world with the same low population growth as in the Al
storylme, but with rapid changes in economic stmcUares toward a service and information economy, with reductions in
material intensity, and the mtroduction of clean and resource-efficient technologies. The emphasis is on global solutions
to economic, social, and envkonmental sustainability, including improved equity, but without additional climate
initiatives.
• The B2 storyline and scenario family describes a world in which the emphasis is on local solutions to economic, social,
and environmental sustainability. It is a world with moderate population growth, intermediate levels of economic
development, and less rapid and more diverse technological change than in the В1 and Al storylines. While the scenario
is also oriented toward environmental protection and social equity, it focuses on local and regional levels.
After determining the basic features and driving forces for each of the four storylines, the team began modeling and quantifying
the storyUnes. This resulted in 40 scenarios, each of which constitutes an alteinative hlteфretation and quantification of a
storyfine. All the hiterpretations and quantifications associated with a single storyline are called a scenario "family" (see Chapter
1 for terminology and Chapter 4 for further details).
After detennining the basic features and driving forces for each
of the four storylines, the team quantified the storylines into
individual scenarios with the help of formal (computer)
models. The six modeling groups that quantified the storylines
are listed in Box 6-2. The six models are representative of
different approaches to modeling emissions scenarios and
different integrated assessment (lA) frameworks in the
literature and include so-called top-down and bottom-up
models. The writing team recommends that IPCC or a similar
international institution should ensure participation of
^ During the approval process of the Summary for Policymakers at
the 5* Session of Working Group III of the IPCC from 8-11 March
2000 in Katmandu, Nepal, it was decided to combine the AIC and
AIG groups into one "fossil intensive" group AlFI in contrast to the
non-fossil group AIT, and select two illustrative scenarios from these
two Al groups to facilitate use by modelers and poHcy makers. This
leads to six scenario groups that constitute the four scenario families,
three of which are in the Al family. The six groups all have "
illustrative scenarios", four of which are marker scenarios. All
scenarios are equally sound. See also Figure SPM-1.
modeling groups around the world, and especially those from
developing countries, in future scenario development and
assessment efforts. Clearly, this would also require resources
specifically to assist modeling groups from developing
countries. Indeed, a concerted effort was made to engage
modeling groups and experts from developing countries in
SRES as a direct response to recommendations of the IPCC
scenario evaluation (Alcamo et al., 1995).
The six models have different regional aggregations. The
writing team decided to group the various global regions into
four "macro-regions" common to all different regional
aggregations across the six models. The four macro-regions
(see Appendix III) are broadly consistent with the allocation of
countries in the United Nations Framework Convention on
Climate Change (UNFCCC, 1997) although the
correspondence is not exact because of changes in the
countries fisted in Annex I of UNFCCC.
All the qualitative and quanthative features of scenarios that
belong to the same family were set to conform to the
corresponding features of the underlying storyline. Together,