Emissions Scenarios - IPCC

176 An Overview of Scenarios
Table 4.1 continued
Harmonization criteria:
1990-2020 2020-2050 2050-2100
Population World 5% 5% 5%
4 SRES regions 10% 10% 10%
GDP World 10% 10% 10%
4 SRES regions 25% 25% 25%
Final Energy World 15% 15% 15%
4 SRES regions 25% 20% 15%
" The AIT scenarios explored cases of increased energy end-use efficiency and therefore share similar levels of energy services, but not final
energy, with the Al marker scenario. As this was an agreed upon (different) feature of this particular scenario group compared to that of the
Al marker, the final energy harmonization criteria does not apply by design. If final energy use is excluded as harmonization criteria for the
scenarios of the AIT scenario group the number of harmonized scenarios increases to 13 (four SRES regions and worid level) and 17 (worid
level only), respectively.
I' Alvl-MiniCAM, Alv2-MiniCAM, and A2-Al-MiniCAM became available only late in the process (after the 15 July 1999 deadline).
Intentionally, they describe futures that ai'e quite different in character from the other scenaiios in their respective families and are therefore
only to a limited degree comparable to other scenarios of the Al and A2 scenario families.
The IMAGE-resuhs for the A2 and B2 scenarios are based on preliminary model experiments done in March 1998. Due to limited resources
it has not been possible to redo these experiments. Hence, the IMAGE-team is not able to provide background data and details for these
scenario calculations and the population and economic growth assumptions are not fully harmonized, as is the case for the IMAGE Al and
Bl scenarios.
•* Deviations from harmonization criteria in one time period are not considered in this classification.
adjusting control parameters, possible diversity still remained
(see Section 4.4.1).
In addition, the Al scenario family developed into different
distinct scenario groups, each based on the Al storyline that
describes alternative developments in future energy systems,
from carbon-intensive development to decarbonization (see
footnote 1). (Similar storyline variations were considered for
other scenario families, but were pursued only to a limited
degree in scenario sensitivity analysis in order to limit the
number of scenarios.) This further increased the richness in
different GHG emissions paths, because this variation in the
structure of the future energy system in itself resulted in a
range of emissions almost as large as that generated through
the variation of other main driving forces, such as population
and economic development. The differentiation into various
scenario groups was introduced into the Al storyline because
of its "high growth with high technology" nature, in which
differences in alternative technology developments translate
into large differences in future GHG emission levels.
As for the storylines, no single scenario was treated as more or
less "probable" than others belonging to the same family.
However, after requests from various user communities to
reduce the number of scenarios to a manageable size, a single
scenario within a family was selected as a representative case
to illusfrate a particular storyline on the basis of the modeling
teams' consensus. These scenarios were named "marker
scenarios" or simply "markers" and were put on the SRES
open process webpage for review. The marker scenario for the
AI scenario storyline was developed using the AIM model; for
the A2 storyhne using the ASF model; for the Bl storyline
using the IMAGE model; and finally for the B2 storyline using
the MESSAGE model (see Table 4-1).
The choice of the markers was based on extensive discussion
within the SRES team:
• Which of the initial quantifications (by the models)
reflected the story best.
• Preference of some of the modeling teams and features
of specific models.
• Range of emissions across all the markers.
• Use of different models for the four markers.
In 1998, the preliminary descriptions and quantifications of the
marker scenarios were posted on the SRES website for the
open process and, in accordance with a decision of the IPCC
Bureau, were in this way made available to climate modelers
for their input in the Third Assessment Report. As a result of
the inputs and comments received through the open process
and by the entire writing team, the marker scenarios have been
successively refined and improved without changmg their
fundamental characteristics in terms of impoitant scenario