The Special Report on Emissions Scenarios (SRES) was a report prepared by the Intergovernmental Panel on Climate Change (IPCC) for the Third Assessment Report (TAR) in 2001, on future emission scenarios to be used for driving global circulation models to develop climate change scenarios. It was used to replace the IS92 scenarios used for the IPCC Second Assessment Report of 1995. The SRES Scenarios were also used for the Fourth Assessment Report (AR4) in 2007, and have been subject to discussion about whether emissions growth since 2000 makes these scenarios obsolete.

The scenarios may be seen here.

[edit] Purpose

Because projections of climate change depend heavily upon future human activity, climate models are run against scenarios. There are 40 different scenarios, each making different assumptions for future greenhouse gas pollution, land-use and other driving forces. Assumptions about future technological development as well as the future economic development are thus made for each scenario. Most include an increase in the consumption of fossil fuels; some versions of B1 have lower levels of consumption by 2100 than in 1990 [2]. Over all the world GDP will increase with a factor between 5-25 in the emission scenario. Some have questionned whether peak oil means that fossil fuel reserves are adequate to support these scenarios ^[1], but this objection is not generally supported ^[2].

These emission scenarios are organized into families, which contain scenarios that are similar to each other in some respects. IPCC assessment report projections for the future are often made in the context of a specific scenario family.

[edit] Scenario families

Scenario families contain individual scenarios with common themes. The six families of scenarios discussed in the IPCC's Third Assessment Report (TAR) and Fourth Assessment Report (AR4) are A1FI, A1B, A1T, A2, B1, and B2.

Scenario descriptions are based on those in AR4, which are identical to those in TAR. ^[3]

[edit] A1

The A1 scenarios are of a more integrated world. The A1 family of scenarios is characterized by:

• Rapid economic growth.
• A global population that reaches 9 billion in 2050 and then gradually declines.
• The quick spread of new and efficient technologies.
• A convergent world - income and way of life converge between regions. Extensive social and cultural interactions worldwide.

There are subsets to the A1 family based on their technological emphasis:

• A1FI - An emphasis on fossil-fuels.
• A1B - A balanced emphasis on all energy sources.
• A1T - Emphasis on non-fossil energy sources.

[edit] A2

The A2 scenarios are of a more divided world. The A2 family of scenarios is characterized by:

• A world of independently operating, self-reliant nations.
• Continuously increasing population.
• Regionally oriented economic development.
• Slower and more fragmented technological changes and improvements to per capita income.

[edit] B1

The B1 scenarios are of a world more integrated, and more ecologically friendly. The B1 scenarios are characterized by:

• Rapid economic growth as in A1, but with rapid changes towards a service and information economy.
• Population rising to 9 billion in 2050 and then declining as in A1.
• Reductions in material intensity and the introduction of clean and resource efficient technologies.
• An emphasis on global solutions to economic, social and environmental stability.

[edit] B2

The B2 scenarios are of a world more divided, but more ecologically friendly. The B2 scenarios are characterized by:

• Continuously increasing population, but at a slower rate than in A2.
• Emphasis on local rather than global solutions to economic, social and environmental stability.
• Intermediate levels of economic development.
• Less rapid and more fragmented technological change than in A1 and B1.

[edit] SRES scenarios and climate change initiatives

While some scenarios assume a more environmentally friendly world than others, none include any climate-specific initiatives, such as the Kyoto Protocol.^[3]

[edit] Criticism

The SRES scenarios were criticised by Ian Castles, and David Henderson.^[4][5][6] The core of their critique was the use of market exchange rates (MER) for international comparison, in lieu of the theoretically favoured PPP exchange rate which corrects for differences in purchasing power.^[7] The IPCC rebutted this criticism^[8][9][10]

The positions in the debate can be summarised as follows. Using MER, the SRES scenarios overstate income differences in past and present, and overestimate future economic growth in developing countries. This, Castles and Henderson argue, leads to an overestimate of future greenhouse gas emissions. The IPCC would have made climate change more dramatic than it is.

However, the difference in economic growth is offset by a difference in energy intensity. Some say these two opposite effects fully cancel^[11], some say this is only partial^[12]. Overall, the effect of a switch from MER to PPP is likely to have a minimal effect on carbon dioxide concentrations in the atmosphere.^[13]

But even if global climate change is not affected, it has been argued^[14] that the regional distribution of emissions and incomes is very different between an MER and a PPP scenario. This would influence the political debate: In a PPP scenario, China and India have a much smaller share of global emissions. It would also affect vulnerability to climate change: in a PPP scenario, poor countries grow slower and would face greater impacts.

[edit] Emissions from 2000-2008

The growth rate of global emissions after 2000 has been about 3%, while the growth rates under these emissions scenarios is between 1.4% and 3.4%. This has attracted attention and could be evidence that these scenarios are too conservative. However, because these emissions scenarios are long-range predictions, it is also possible that the recent trend is a short-term trend that will not result in a long term deviation from the possibilities described by these emissions scenarios. ^[15]

[edit] References

[edit] External links

• Report website
• Terms of reference
• "What is an emission scenario?" by Jean-Marc Jancovici