IPCC Special Report on Emissions Scenarios

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4.2. SRES Scenario Taxonomy

4.2.1. Storylines

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.

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 parameters.

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):

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 1).

Set SRES Total

A2 B1 B2
Scenario Group A1C A1G A1B A1T A2 B1 B2

Globally Harmonized Scenariosa 2 3 6 2 2 7 4 26
Other Scenariosb 1 0 2 1 4 5 4 14

Total Scenarios 3 3 8 3 6 9 8 40
(Different Models Used) (3) (3) (6) (3) (5) (6) (6) (6)
Scenario characteristics:c

Population growth low low low low high low medium
GDP growth very high very high very high very high medium high medium
Energy use very high very high very high high high low medium
Land- use changes low-medium low-medium low low medium/high high medium
Resource availabilityd high high medium medium low low medium
Pace and direction of technological rapid rapid rapid rapid slow medium medium
change favoring coal oil & gas balanced non-fossils regional 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 emphasis.

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 4-3).

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:

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.

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