Emissions Scenarios - IPCC

Technical Summary 25
• use a variety of models to reflect methodological
pluralism and uncertainty;
• incorporate input from a wide range of scientific
disciplines and expertise from non-academic sources
through an open process;
• exclude additional initiatives and policies specifically
designed to reduce climate change;
• cover and describe to the extent possible a range of
policies that could affect climate change although they
are targeted at other issues, for example, reductions in
SO, emissions to limit acid rain;
• cover as much as possible of the range of major
underlying driving forces of emission scenarios
identified in the open literature;
• be transparent with input assumptions, modeling
approaches, and results open to external review;
• be reproducible - document data and methodology
adequately enough to allow other researchers to
reproduce the scenarios; and
• be internally consistent - the various input assumptions
and data of the scenarios are internally consistent to the
extent possible.
The writing team agreed that the scenario formulation process
would consist of five major components:
• review of existing scenarios in the literature;
• analysis of their main characteristics and driving
forces;
• formulation of narrative "storylines" to describe
alternative futures;
• quantification of storylines with different modeling
approaches; and
• "open" review process of emissions scenarios and their
assumptions
As is evident from the components of the work program, there
was agreement that the process be an open one with no single
"official" model and no exclusive "expert teams." In 1997 the
IPCC advertised in a number of relevant scientific journals and
other publications to solicit wide participation in the process.
To facilitate participation and improve the usefulness of the
new scenarios, the SRES web site (www.sres.ciesin) was
created. In addition, members of the writing team published
much of the background work used for formulating SRES
scenarios in the peer-reviewed literature^ and on web sites (see
Appendix IV). Finally, the revised set of scenarios, the web
sites, and the draft of this report have been evaluated through
the IPCC expert and government review processes. This
process resulted in numerous changes and revisions of the
report. In particular, during the approval process of Ihe
Summary for Policymakers (SPM) in March 2000 at the 5"'
Session of the WG III in Katmandu changes in this SPM were
agreed that necessitated some changes in the underlying
document, including this Technical Summary. These changes
have been implemented in agreement with the Lead Authors.
5. Scenario Literature Review and Analysis
The first step in the formulation of the SRES scenarios was the
review and the analysis of the published literature and the
development of the database with more than 400 emissions
scenarios that is accessible through the web site (wwwcger.nies.go.jp/cger-e/db/ipcc.html);
190 of these extend to
2100 and are considered in the comparison with the SRES
scenarios in the subsequent Figures. Chapters 2 and 3 give a
more detailed description of the Hterature review and analysis.
Figure TS-1 shows the global energy-related and industrial
COj emission paths from the database as "spaghetti" curves for
the period to 2100 against the background of the historical
emissions from 1900 to 1990. These curves are plotted against
an index on the vertical axis rather than as absolute values
because of the large differences and discrepancies for the
values assumed for the base year 1990. These sometimes arise
from genuine differences among the scenarios (e.g., different
data sources, definitions) and sometimes from different base
years assumed in the analysis or from alternative calibrations.'*
The differences among the scenarios in the specification of the
base year illustrate the large genuine scientific and data
uncertainty that surrounds emissions and their main driving
forces captured in the scenarios. The literature includes
scenarios with additional climate polices, which are sometimes
referred to as mitigation or intervention scenarios.
There are many ambiguities associated with the classification
of emissions scenarios into those that include additional
climate initiatives and those that do not. Many cannot be
classified in this way on the basis of the information available
from the database. Figure TS-1 indicates the ranges of
emissions in 2100 from scenarios that apparently include
additional climate initiatives (designated as "intervention"
emissions range), those that do not ("non-intervention") and
those that caimot be assigned to either of these two categories
("non-classified"). This classification is based on the
subjective evaluation of the scenarios in the database by the
members of the writing team and is explained in Chapter 2.
The range of the whole sample of scenarios has significant
^ Alcamo and Nakicenovic, 1998; Alcamo and Swart, 1998; Anderson,
1998; Gaffin, 1998; Gregory, 1998; Gregory and Rogner, 1998;
Grübler, 1998; Michaelis, 1998; Monta and Lee, 1998; Nakicenovic et
al, 1998; Price et al, 1998; de Vries et al., 2000; Fenhann, 2000; Jiang
et al, 2000, Jung et al, 2000; Kram et al., 2000; Mori, 2000;
Nakicenovic, 2000; Riahi and Roehrl, 2000; Roehrl and Riahi, 2000;
Sankovski et al., 2000.
The 1990 emissions from energy production and use are estimated
by Marland etal. (1994) at 5.9 GtC excluding cement production. The
1990 base year values in the scenarios reviewed range from 4.8
(CETA/EMF14, Scenario MAGICO CO^) to 6.4 GtC
(ICAM2/EMF14), see Dowlatabadi et al, 1995; Peck and Teisberg,
1995.