4.2. SRES Scenario Taxonomy
The primary purpose of developing multiple scenario families was to explore
the uncertainties behind potential trends in global developments and GHG emissions,
as well as the key drivers that influence these (see also Chapter
1, Section 1.7.2). The writing team decided that narrative storylines, based
on the futures and scenario literature, would be the most coherent way to describe
their scenarios, for the following reasons.
- To help the team to think more coherently about the complex interplay between
scenario driving forces within and across alternative scenarios and to enhance
the consistency in assumptions for different parameters.
- To make it easier to explain the scenarios to the various user communities
by providing a narrative description of alternative futures that goes beyond
quantitative scenario features.
- To make the scenarios more useful, in particular, to analysts contributing
to IPCC WGs II and III. The demographic, social, political, and technological
contexts described in the scenario storylines are all-important in the analysis
of the effects of policies to either adapt to climate change or to reduce
- To provide a guide for additional assumptions to be made in detailed climate-impact
and mitigation analyses, because at present no model or scenario can possibly
respond to the wide variety of informational and data needs of the different
user communities of long-term emissions scenarios.
The four scenario families presented in this report are representative of a
broad range of scenarios found in the literature, but they are not directly
based on any particular published scenario taxonomy or set of scenarios. Rather,
the storylines of each scenario family were developed on the basis of the general
knowledge of this literature, and on the personal experience and creativity
within the writing team. The writing team spent the better part of the first
year (1997) formulating the storylines, which during the following two years
were revised iteratively with the scenario development until the completion
of the report.
Four brief "future histories" captured by the SRES storylines differ in how
global regions interrelate, how new technologies diffuse, how regional economic
activities evolve, how protection of local and regional environments is implemented,
and how demographic structure changes. The "qualitative" storyline characteristics
include various political, social, cultural, and educational conditions (e.g.,
type of governance, social structure, and educational level) that often cannot
be defined in strictly quantitative terms and do not directly "drive" GHG emissions.
These qualitative variables, however, participate in complex "cause-effect"
relationships with quantitative emission drivers (e.g., economic activities,
population levels, energy consumption). Their explicit inclusion in the scenario
development process not only makes scenarios more "plausible" and "believable,"
but also ensures they do not become an arbitrary numeric combination of quantitative
The SRES storylines do not include explicit policies to limit GHG emissions
or to adapt to the expected global climate change, reflecting the SRES Terms
of Reference (see Appendix I). However, the storyline
demographic, social, economic and technological profiles can be used in other
studies to develop and evaluate climate-change mitigation and adaptation measures
and policies. Such evaluation would require additional (prescriptive) assumptions
about policies and measures to affect future climates and human responses to
climate change now absent from the storylines.
|Box 4-2: "Neutrality" of the SRES Scenarios
The SRES scenarios are intended to exclude catastrophic futures. Such catastrophic
futures feature prominently in the literature. They typically involve large-scale
environmental or economic collapses, and extrapolate current unfavorable
conditions and trends in many regions. Prominent examples of such scenarios
include "Retrenchment" (Kinsman, 1990), "Dark Side of the Market World"
or "Change without Progress" (Schwartz, 1991), "Black and Grey" (Godet et
al., 1994), "Global Incoherence Scenario" (Peterson, 1994), "New World Disorder"
(Schwartz, 1996), "A Visit to Belindia" (Pohl, 1994), the future evoked
by the description of the current situation in parts of West-Africa and
Central Asia (Kaplan, 1996), "Barbarization" (Gallopin et al., 1997), "Dark
Space" (Glenn and Gordon, 1999), "Global Fragmentation" (Lawrence et al.,
1997), and "A Passive Mean World" (Glenn and Gordon, 1997, 1999). In this
last scenario the world is carved up into three rigid and distinct trading
blocs, with fragmented political boundaries and out-of-control ethnic conflicts.
In "Global Crisis" (de Jong and Zalm, 1991; CPB, 1992) protectionism leads
to a vicious circle of slowing economic growth and eventually breakdown.
Many of these scenarios suggest that catastrophic developments may draw
the world into a state of chaos within one or two decades. In such scenarios
GHG emissions might be low because of low or negative economic growth, but
it seems unlikely they would receive much attention in the light of more
immediate problems. Hence, this report does not analyze such futures.
All four SRES "futures" represented by the distinct storylines are treated
as equally possible and there are no "central," "business-as-usual,""surprise,"
or "disaster" futures (examples of which are given in Box 4.2).
All of the storylines have features that can be interpreted as "positive" or
"negative" and they play out different tendencies and changes in part visible
in the world today. To avoid the tendency to overemphasize "positive" or "negative"
features of individual storylines, their titles were kept simple. Many attempts
were made to capture the spirit of each storyline with a short and snappy title,
but no single title was found to reflect adequately the complex mix of characteristics
of any storyline.
By 2100 the world will have changed in ways that are difficult to imagine,
as difficult as it was at the end of the 19th century to imagine the changes
of the 20th century. However, each storyline takes a different direction of
future developments so that they differ in an increasingly irreversible way.
They describe divergent futures that reflect a significant portion of the underlying
uncertainties in the main driving forces. The differences among the storylines
cover a wide range of the key "future" characteristics, such as technology,
governance, and behavioral patterns. Hence the plausibility or feasibility of
the storyline assumptions should be viewed with an "open mind," not from a narrow
interpretation of current situations and trends in economic conditions, technology
developments, and social and governing structures.
The main characteristics of future developments that take distinct development
paths in the four storylines include (see also Table
4-2 for an overview):
- Nature of the global and regional demographic develop-ments in relation
to other characteristics of the storyline.
- Extent to which economic globalization and increased social and cultural
interactions continue over the 21st century.
- Rates of global and regional economic developments and trade patterns in
relation to the other characteristics of the storyline.
- Rates and direction of global and regional technological change, especially
in relation to the economic development prospects.
- Extent to which local and regional environmental concerns shape the direction
of future development and environmental controls.
- Degree to which human and natural resources are mobilized globally and regionally
to achieve multiple development objectives of each storyline.
- Balance of economic, social, technological, or environmental objectives
in the choices made by consumers, governments, enterprises, and other stakeholders
|Table 4- 2: Overview of SRES scenario
quantifications. Shown for each scenario is the name of the storyline and
scenario family, the name of the scenario group, number of harmonized and
total scenarios in the respective group, by how many different modeling
approaches they were developed, and the main (qualitative) characteristics
of each of the scenario groups. Please note that A1C and A12G were combined
into one fossil- intensive A1FI group in the SPM (see also footnote
|Globally Harmonized Scenariosa
|(Different Models Used)
|Land- use changes
|Pace and direction of technological
||oil & gas
||efficiency & dematerialization
||"dynamics as usual"
A. Globally Harmonized Scenarios share common major input assumptions
that describe a particular scenario family at the global level (i. e.,
global population and GDP within agreed bounds of 5% and 10%, respectively)
compared to the marker scenarios over the entire time horizon 1990 to
2100 (deviation in one time period being tolerated). To further scenario
comparability more stringent harmonization criteria were applied where
population, GDP, and final energy trajectories were harmonized at the
level of the four SRES regions.
B. Other Scenarios offer alternative interpretations of a scenario storyline
for global population and GDP either in its time path or in their levels
(or both). Scenarios A2- AIM, A2- MiniCAM and B2- MiniCAM deviate only
slightly from the global harmonization criterion for between two to three
time steps. Hence these scenarios can be considered as "almost" harmonized
and comparable with the other harmonized scenarios.
C. Scenario characteristics as applied to harmonized scenarios. Other
scenarios explore sensitivities of adopting alternative inpu t assumptions
than captured in this classification.
D. Resource availability of conventional and unconventional oil and gas.
|Box 4-3: Globalization Issues With the convergence
in governments' economic policies in the 1990s, combined with the rapid
development of communication networks, it is perhaps not surprising that
an extensive poll of scenarios by the Millennium Institute suggested "globalization"
as the main driving force that will shape the future (Glenn and Gordon,
1997, 1999). However, some scenarios in the literature explore the possibility
that unfettered markets, usually seen as an integral element of "globalization,"
might destabilize society in ways that endanger the process (Mohan Rao,
1998). In UNESCO's 1998 World Culture Report, it is noted that communities
are increasingly emphasizing their cultural individuality; meanwhile, communication
and travel are resulting in interactions between communities that result
in the evolution of new "local" cultures (UNESCO, 1998). Huntington (1996)
asserts that continental regional cultures may determine the shape of future
geopolitical developments rather than globalization.
Thus, the storylines describe developments in many different economic, technical,
environmental, and social dimensions. Consequently, they occupy a multidimensional
space and no simple metric can be used to classify them. Even though they occupy
such a multidimensional space along many driving forces relevant for GHG emissions,
it is useful here to highlight just two dimensions. The first refers to the
extent of economic convergence and social and cultural interactions across the
regions and the second to the balance between economic objectives and environmental
and equity objectives. Possible names for these two dimensions could be "globalization"
(Box 4-3) and "sustainability," respectively (Box
4-4). As these two expressions are not necessarily viewed by everyone as
being value-free, the two dimensions could alternatively be designated simply
as a more global or more regional orientation and as a more economic or a more
environmental orientation (see Figure 4-1). These
dimensions are important in the SRES scenarios. Nevertheless, there was considerable
resistance in the SRES writing team against such a simplistic classification
of storylines, so it is presented here for illustrative purposes only. These
distinctions are, in a sense, artificial. For example, both economic and environmental
objectives are pursued in all scenarios, albeit with different levels of relative
The extent to which the currently observed global and regional orientations
will prevail in the 21st century is pertinent to the distinction between the
A1 and B1 scenario families on one side and A2 and B2 families on the other
side. While the A1 and B1 storylines, to different degrees, emphasize successful
economic global convergence and social and cultural interactions, A2 and B2
focus on a blossoming of diverse regional development pathways (see Box
|Box 4-4: Sustainability Issues Recent decades
have seen considerable growth in discourse of environmental and social issues,
represented at the global level by several high-level United Nations (UN)
meetings on social and economic development and environmental sustainability
(UNCED, 1992; UN, 1994, 1995; Leach, 1998; Munasinghe and Swart,2000). The
range of participants has expanded from the most closely involved government
ministries, businesses, and environmental NGOs to include a broad range
of representation by different ministries, local government, businesses,
professions, and community groups. Increased interest in sustainability
issues can lead to all kinds of socio-economic and technological changes
that may not be aimed explicitly at reducing GHG emissions, but which may
in effect contribute significantly to such reductions.
The extent to which the currently observed economic and environmental orientations
will prevail in the 21st century is pertinent to the distinction between A1
and A2 scenario families on one side and B1 and B2 scenario families on the
other side. In the B1 and B2 storylines this transition is pursued, to different
degrees, through a successful translation of global concerns into local actions
to promote environmental sustainability. Alternatively, in the A1 and A2 storylines
the emphasis remains, again to different degrees, on sustained economic development
and achievement of high levels of affluence throughout the world, where environmental
priorities are perceived as less important than those of economic development
(see Box 4-4).
In short, each of the storylines can be summarized as follows:
The A1 storyline 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 underlying themes are convergence
among regions, capacity building, and increased cultural and social interactions,
with a substantial reduction in regional differences in per capita income.
The A1 scenario family develops into four groups that describe alternative
directions of technological change in the energy system.1
- The A2 storyline and scenario family describes a very heterogeneous world.
The underlying theme is self-reliance and preservation of local identities.
Fertility patterns across regions converge very slowly, which results in high
population growth. Economic development is primarily regionally oriented and
per capita economic growth and technological change are more fragmented and
slower than in other storylines.
- The B1 storyline and scenario family describes a convergent world with the
same low population growth as in the A1 storyline, but with rapid changes
in economic structures toward a service and information economy, with reductions
in material intensity, and the introduction of clean and resource-efficient
technologies. The emphasis is on global solutions to economic, social, and
environmental sustainability, including improved equity, but without additional
- 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 B1 and A1 storylines. While the scenario is also oriented toward environmental
protection and social equity, it focuses on local and regional levels.
These storylines are presented in more detail in Section
4.3, which includes their original quantitative indicators that served as
input to the scenario quantification process.