Of the 124 global futures scenarios in the database, 35 provide some kind of projection of future GHG (usually CO₂) emissions. These projections range from narrative descriptions (e.g., “emissions continue to rise”) to numerical estimates. Figure 2.9 shows global carbon dioxide emissions projections from the scenarios that provide numerical estimates.

Most (22) of these scenarios project increased emissions, but several (13) foresee declining emissions. All but one of the latter scenarios are Sustainable Development scenarios in which there is a concerted policy effort towards emission reduction, innovation in energy development towards improved efficiency and conservation, and/or alternatives to fossil fuels. The exception is a High-Tech Optimist scenario in which energy efficiency technologies and a shift to low- and non-fossil fuels bring about declining emissions.

The Sustainable Development scenarios that project declining emissions are in general characterized by increased co-operation and political participation; many assume that there is strong international agreement on the environment and development in general and climate change in particular. There is improved environmental quality and equity and, in several scenarios, increased material affluence globally (although some scenarios indicate a decline in consumerism). Population continues to grow but at slower rates and stabilizes at relatively low levels. In most scenarios significant developments of energy efficiency, energy conservation, and alternative energy technologies are key to emission reduction; a number of scenarios assume a tax on fossil fuels.

Table 2.4 summarizes the apparent relationships between emissions and scenario dimensions. It is important to note that there is considerable variety among the scenarios; Table 2.4 therefore shows relationships that were in the majority, but not necessarily all, of the scenarios. It should also be noted that the relationships shown in Table 2.4 do not by themselves prove causation; they simply reflect what the majority of scenarios with rising and falling GHG emissions, respectively, indicate for each scenario dimension.

Table 2.4: Factors associated with changing GHG emissions in global futures scenarios
Factor	Rising GHGs	Falling GHGs
Economy	Growing, post-industrial economy with globalization, (mostly) low government intervention, and generally high level of competition	Some scenarios show rising GDP, others show economic activity limited to ecologically sustainable levels; generally high level of government intervention
Population	Growing population with high level of migration	Growing population that stabilizes at relatively low level; low level of migration
Governance	No clear pattern in governance	Improvements in citizen participation in governance, community vitality, and responsiveness of institutions
Equity	Generally declining income equality within nations and no clear pattern in social equity or international income equality	Increasing social equity and income equality within and among nations
Conflict/Security	High level of conflict and security activity (mostly), deteriorating conflict resolution capability	Low level of conflict and security activity, improved conflict resolution capability
Technology	High level of technology, innovation, and technological diffusion	High level of technology, innovation, and technological diffusion
Resource Availability	Declining renewable resource and water availability; no clear pattern for non-renewable resource and food availability	Increasing availability of renewable resources, food and water; no clear pattern for non-renewable resources
Environment	Declining environmental quality	Improving environmental quality

The major visible difference has to do with environmental impacts. As might be expected, pollution and the risk of ecological collapse are generally high in scenarios which show rising GHG emissions, and low in scenarios which show falling GHG emissions. Water availability and biodiversity decline in the scenarios with rising GHG emissions, and rise or stay the same in the scenarios with falling GHG emissions.

On a different front, in the scenarios with rising GHG emissions, conflict and security activity are generally high, while government intervention in the economy and income equality (within nations) are generally low. The reverse is true in the scenarios with falling GHG emissions, which also show improving equity between North and South. This would be expected from the fact that all but one of these scenarios are Sustainable Development scenarios.

Chapter 3 of the SRES discusses the relationships between GHG emissions and a number of driving forces, including population, economic and social development (including equity), and technology. What is clear from that discussion, which is consistent with the evidence summarized in Table 2.4, is that the impacts on GHG emissions of changes in these underlying driving forces are complex.

These complex relationships suggest that the choice of future “world” is more fundamental than the choice of a few driving forces in determining GHG emissions. The wide range of emissions in the various SRES baseline scenarios also demonstrates this point. Choices about DES are crucial, not just for the underlying conditions which give rise to emissions, but also for the nature and severity of climate change impacts, and the success of particular mitigation and adaptation policies. This finding is consistent with the discussion in Chapter 1, which suggests the central importance of DES issues in any consideration of climate change.

It is important therefore that emission scenarios consider qualitative aspects that are potentially important for future GHG emissions and mitigation policies. One way to do this is to link these scenarios with the broader global futures scenarios. However, this will be difficult because there are few areas of overlap, as a result of the very different natures of the two kinds of scenarios. Perhaps a more fruitful way of incorporating qualitative dimensions into quantitative scenarios, already pursued by the Global Scenarios Group and others, as well as in the SRES, is to develop quantitative estimates of key variables based on qualitative descriptions of future worlds.

A survey of the global futures literature has yielded a number of insights that are relevant to GHG emission scenarios and sustainable development. First, a wide range of future conditions has been identified by futurists, ranging from variants of sustainable development to collapse of social, economic, and environmental systems. Since future values of the underlying socio-economic drivers of emissions may vary widely, it is important that GHG emission scenarios in particular, and climate change analysis in general, not limit themselves to a narrow range of possible futures, but consider the implications for mitigation of quite different sets of future conditions. In turn, climate policies should be designed so that they are resilient against widely different future conditions.

Second, the global futures scenarios describe a wide range of worlds, from pessimistic to optimistic, that are consistent with rising GHG emissions and a smaller range of (generally optimistic) worlds that are consistent with falling emissions. Scenarios that show falling emissions tend to show improved governance, increased equity and political participation, reduced conflict, conditions supportive of lower birth rates, and improved environmental quality. Scenarios with rising emissions generally show reduced environmental quality and equity within nations and increased conflict, and are more mixed with respect to governance and international equity. Both types of scenarios generally indicate continued technological development. The Sustainable Development scenarios suggest that sustainable development approaches are feasible, and can lead to futures characterized by relatively low emissions. A key implication is that sustainable development policies, taken generally, can make a significant contribution to emission reduction.

Third, scenarios do not all show a positive relationship between emissions and economic and population growth, as is commonly assumed (see also the discussion of the Kaya identity in Section 2.3.2.1 of this chapter). This is largely because, in the scenarios with declining emissions and rising population and economic activity, policy, lifestyle choices, and technological development act to reduce emissions through efficiency improvements, energy conservation, shifts to alternative fuels, and shifts to post-industrial economic structures. This suggests that different combinations of driving forces are consistent with low emission scenarios, which agrees with the SRES findings. The implication of this would seem to be that it is important to consider the linkage between climate policy and other policies and conditions associated with the choice of future paths in a general sense. In other words, low emission futures are associated with a whole set of policies and actions that go beyond the development of climate policy itself.

In general, the global futures scenarios provide more comprehensive coverage of the issues relevant to sustainable development than the general mitigation scenarios described in section 2.3. They therefore represent an important complement to the quantitative emission scenarios. However, there are significant difficulties involved in trying to connect the mainly narrative-based scenarios discussed in this section with the more quantitatively oriented scenarios discussed earlier. In this connection, the work of the Global Scenarios Group, the SRES, and others in linking narrative scenarios addressing social, environmental, and economic elements of sustainable development with model “quantifications” appears to point the way to the type of work needed to better assess the implications of GHG mitigation for sustainable development and vice versa. Section 2.5 below discusses the SRES scenarios and process, as well as mitigation scenarios that were developed on the basis of the SRES baseline scenarios.

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