Climate change scenario

See also: Climate change mitigation scenarios

This article is about climate change scenarios. Socioeconomic scenarios are used by analysts to make projections of future greenhouse gas (GHG) emissions and to assess future vulnerability to climate change (Carter et al., 2001:151).^[1] Producing scenarios requires estimates of future population levels, economic activity, the structure of governance, social values, and patterns of technological change. Economic and energy modelling (such as via the World3 or the POLES models) can be used to analyse and quantify the effects of such drivers.

Emissions scenarios

Global futures scenarios

These scenarios can be thought of as stories of possible futures. They allow the description of factors that are difficult to quantify, such as governance, social structures, and institutions. Morita et al. (2001:137-142) assessed the literature on global futures scenarios.^[2] They found considerable variety among scenarios, ranging from variants of sustainable development, to the collapse of social, economic, and environmental systems. In the majority of studies, the following relationships were found:

• Rising GHGs: This was associated with scenarios having a growing, post-industrial economy with globalization, mostly with low government intervention and generally high levels of competition. Income equality declined within nations, but there was no clear pattern in social equity or international income equality.
• Falling GHGs: In some of these scenarios, GDP rose. Other scenarios showed economic activity limited at an ecologically sustainable level. Scenarios with falling emissions had a high level of government intervention in the economy. The majority of scenarios showed increased social equity and income equality within and among nations.

Morita et al. (2001) noted that these relationships were not proof of causation.

No strong patterns were found in the relationship between economic activity and GHG emissions. Economic growth was found to be compatible with increasing or decreasing GHG emissions. In the latter case, emissions growth is mediated by increased energy efficiency, shifts to non-fossil energy sources, and/or shifts to a post-industrial (service-based) economy.

Factors affecting emissions growth

• Development trends: In producing scenarios, an important consideration is how social and economic development will progress in developing countries (Fisher et al., 2007:176).^[3] If, for example, developing countries were to follow a development pathway similar to the current industrialized countries, it could lead to a very large increase in emissions.
• GHG emissions and economic growth: Emissions do not only depend on the growth rate of the economy. Other factors are listed below:
  • Structural changes in the production system.
  • Technological patterns in sectors such as energy.
  • Geographical distribution of human settlements and urban structures. This affects, for example, transportation requirements.
  • Consumption patterns: e.g., housing patterns, leisure activities, etc.
  • Trade patterns: the degree of protectionism and the creation of regional trading blocks can affect availability to technology.

Baseline scenarios

A baseline scenario is used as a reference for comparison against an alternative scenario, e.g., a mitigation scenario (IPCC, 2007c:810).^[4] Fisher et al. (2007:178-194) assessed the baseline scenarios literature.^[3] They found that baseline CO₂ emission projections covered a large range. Factors affecting these emission projections are described below:

• Population projections: All other factors being equal, lower population projections result in lower emissions projections.
• Economic development: Economic activity is a dominant driver of energy demand and thus of GHG emissions.
• Energy use: Future changes in energy systems are a fundamental determinant of future GHG emissions.
  • Energy intensity: This is the total primary energy supply (TPES) per unit of GDP (Rogner et al., 2007:107).^[5] In all of the baseline scenarios Fisher et al. (2007) assessed, energy intensity was projected to improve significantly over the 21st century. The uncertainty range in projected energy intensity was large.
  • Carbon intensity: This is the CO₂ emissions per unit of TPES. Compared with other scenarios, Fisher et al. (2007) found that the carbon intensity was more constant in scenarios where no climate policy had been assumed. The uncertainty range in projected carbon intensity was large. At the high end of the range, some scenarios contained the projection that energy technologies without CO₂ emissions would become competitive without climate policy. These projections were based on the assumption of increasing fossil fuel prices and rapid technological progress in carbon-free technologies. Scenarios with a low improvement in carbon intensity coincided with scenarios that had a large fossil fuel base, less resistance to coal consumption, or lower technology development rates for fossil-free technologies.
• Land-use change: Land-use change plays an important role in climate change, impacting on emissions, sequestration and albedo. One of the dominant drivers in land-use change is food demand. Population and economic growth are the most significant drivers of food demand.^{[6][dubious – discuss]}

References

1. ^ Carter, T.R. et al. (2001). "Developing and Applying Scenarios. In: Climate Change 2001: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Third Assessment Report of the Intergovernmental Panel on Climate Change [J.J. McCarthy et al. Eds."]. Cambridge University Press, Cambridge, U.K., and New York, N.Y., U.S.A.. http://www.ipcc.ch/publications_and_data/publications_and_data_reports.htm. Retrieved 2010-01-10. 
2. ^ Morita, T. et al. (2001). "Greenhouse Gas Emission Mitigation Scenarios and Implications. In: Climate Change 2001: Mitigation. Contribution of Working Group III to the Third Assessment Report of the Intergovernmental Panel on Climate Change [B. Metz et al. Eds."]. Cambridge University Press, Cambridge, U.K., and New York, N.Y., U.S.A.. http://www.ipcc.ch/publications_and_data/publications_and_data_reports.htm. Retrieved 2010-01-10. 
3. ^ ^{a b} Fisher, B.S. et al. (2007). "Issues related to mitigation in the long term context. In: Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [B. Metz et al. Eds."]. Cambridge University Press, Cambridge, U.K., and New York, N.Y., U.S.A.. http://www.ipcc.ch/publications_and_data/publications_and_data_reports.htm. Retrieved 2009-05-20. 
4. ^ IPCC (2007c). "Annex. In: Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [B. Metz et al. Eds."]. Cambridge University Press, Cambridge, U.K., and New York, N.Y., U.S.A.. http://www.ipcc.ch/publications_and_data/publications_and_data_reports.htm. Retrieved 2009-05-20. 
5. ^ Rogner, H.-H. et al. (2007). "Introduction. In: Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [B. Metz et al. Eds."]. Cambridge University Press, Cambridge, U.K., and New York, N.Y., U.S.A.. http://www.ipcc.ch/publications_and_data/publications_and_data_reports.htm. Retrieved 2009-05-20. 
6. ^ Fisher, B.S. et al. (2007). ""3.2.1.6 Land-use change and land-use management." In [book chapter: "Issues related to mitigation in the long term context." In [book]: "Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [B. Metz et al. Eds.]""]. Print version: Cambridge University Press, Cambridge, U.K., and New York, N.Y., U.S.A.. This version: IPCC website. http://www.ipcc.ch/publications_and_data/ar4/wg3/en/ch3s3-2-1-6.html. Retrieved 2010-03-18.