Emissions Scenarios - IPCC

80 An Overview of the Scenario Literature
significant literature on narrative scenarios. Both scenario types
have in common that they are generally careñiUy constructed
descriptions of possible future developments within the bounds
of explicit assumptions and ckcumstances (see Chapter 1 for a
more detailed discussion about scenarios). The difference is that
the quantitative scenarios are usually developed with the help of
formal models so as to assign internally consistent values to the
various scenario characteristics.
The SRES scenarios employ both approaches - a storyline that
gives a broad, nairative, and qualitative scenario description
plus a number of quantifications of each storyline with six
different models. Thus, even though both narrative stories and
quantitative scenarios are an integral part of the SRES
emissions scenarios, the literature review focused on the
documentation and the assessment of quantitative scenarios,
for two reasons. First, it was not possible to devise a
classification system that would allow the documentation of
many different forms of natjative scenarios. Second, the SRES
objective was to develop a set of numeric emissions scenarios
for use in the IPCC and other assessments of climate change.
Therefore, in this chapter the focus is only on the literature
review of quantitative scenarios. A more detailed discussion of
narrative scenarios is given in Chapter 4; it deals with the four
SRES storylines and how they are related to recent work in the
area of qualitative scenarios.
The literature on quantitative scenarios is large indeed. This
assessment is focused on the scenarios that extend at least to
2020, but about 10 scenarios with a shorter time horizon of
2010 are also included in the database. In addition, most of the
scenarios have a global coverage, although a few regional
scenarios are included to enhance the coverage of some parts of
the world. These criteria narrowed considerably the number of
global and regional GHG emissions scenarios witii sufficient
information to be included m the scenario literature review.
This scenario literature review and evaluation is the second
undertaken by the IPCC. The first was conducted to evaluate
the IS92 set of scenarios in comparison to other GHG
emissions scenarios found in the literature (Alcamo et al.,
1995)4 It was completed in 1994 and included a
comprehensive evaluation of GHG emissions and their main
driving forces. This second review and evaluation builds upon
and extends the earlier IPCC assessment. Consequently, an
effort was made in the present review to include especially the
GHG emissions scenarios published since the presentation of
the IS92 scenarios.
2.2. General Overview of Scenarios
The construction of scenarios to investigate altemative future
developments under a set of assumed conditions dates far back.
' The IS92 scenarios have also been analyzed with regard to shortterm
adequacy (see Gray, 1998).
Scenarios are one of the main tools used to address the
complexity and uncertainty of future challenges. The first
scenarios were probably designed to help plan military
operations, often called "war games." Today, scenarios are used
regularly by military organizations around the world for
training and planning purposes. Military strategists and
teachers often use very sophisticated computer models to
develop scenarios for a multitude of different purposes.
Scenarios are also increasingly used by enterprises around the
world for many commercial puiposes. Perhaps the most
famous example is that of the Shell Group in the wake of the
so-called oil crisis, which used scenarios to plan the corporate
response strategies (Jefferson, 1983; Schwartz, 1991). Today,
the use of scenarios is quite widespread.. Many scenarios,
particularly those developed for enterprises in the energy
sector, are quantitative and include GHG emissions. Recently,
the World Business Council for Sustainable Development
(WBCSD) presented a set of scenarios developed in
collaboration with 35 major corporations (WBCSD, 1998).
The SRES scenario database documents a number of such
scenarios that are in the public domain and have been
published.
During the past three decades many global studies have used
scenarios as a tool to assess future CO^ (and in a few cases also
other GHG) emissions. One of the fnst such global studies was
Energy in a Finite World, conducted by the Intemational
Institute of Applied Systems Analysis (IIASA) during the late
1970s (Hafele et al, 1981). Another influential series of
scenarios that included the assessment of COj emissions was
developed by the Worid Energy Council (WEC, 1993).
Recently, IIASA and WEC jointly presented a set of global and
regional scenarios that were developed with a set of integrated
assessment models and then reviewed and revised thi'ough 11
regional expert groups (Nakicenovic et al, 1998b). Another
recent set of three scenarios, based on elaborate narrative
stories that described altemative futures, was developed by the
Global Scenario Group (Raskin et al., 1998) and received
considerable attention.
Scenarios of future emissions played an important role from
the beginning of the IPCC work. \n 1990, the IPCC initiated
the development of its first set of GHG emissions scenarios
designed to serve as inputs to general circulation models
(GCMs) and facilitate the assessments of climate-change
impacts (Houghton et ai, 1990). Two years later, in 1992, the
IPCC approved six new emissions scenarios (IS92) that
provided altemative emissions trajectories for the years 1990
through 2100 for such radiatively active gases as COj, carbon
monoxide (CO), methane (CH^), nitrous oxide (N2O), nitrogen
oxides (N0^), and sulfur dioxide (SOj) (Leggett et al, 1992).
They were widely used by atmospheric and climate scientists
in the preparation of scenarios of atmospheric composition and
climate change (Alcamo et al, 1995). In many ways, the IS92
scenarios were pathbreaking. They were the first global
scenarios to provide estimates of the full suite of GHGs and at
the time were the only scenarios to provide emissions