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.
The scenarios may be seen [http://www.grida.no/climate/ipcc/emission/005.htm here] .
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 [http://www.grida.no/climate/ipcc_tar/wg1/figspm-5.htm] . Over all the world GDP will increase with a factor between 5-25 in the emission scenario. It is questionable whether this form of assumptions will hold as several limits to growth appears to be upon the world Fact|date=September 2007. Peak Oil is for instance not discussed in the emission scenarios. Brandt and Farrell (2007, Climatic Change, 84: 241-363) show that this is not a serious omission. [Brandt and Farrell (2007, Climatic Change, 84: 241-363)]
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.
cenario 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. [cite web |url=http://www.ipcc.ch/SPM2feb07.pdf |title=Climate Change 2007: The Physical Science Basis - Summary for Policymakers |accessdate=2007-02-02 |year=2007 |publisher=Intergovernmental Panel on Climate Change] ]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.
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.
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.
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 B1 and A1.
RES 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.[cite web |url=http://www.ipcc.ch/SPM2feb07.pdf |title=Climate Change 2007: The Physical Science Basis - Summary for Policymakers |accessdate=2007-02-02 |year=2007 |publisher=Intergovernmental Panel on Climate Change] ]Controversy
The SRES scenarios were severely criticised by Ian Castles, formerly Australian Statistician, and David Henderson, formerly Chief Economist at the OECD. [ [http://www.lavoisier.com.au/papers/articles/IPPCissues.html Letters to the IPCC] ] [Castles and Henderson (2003), Energy and Environment, 14:159-185] [Castles and Henderson (2003), Energy and Environment, 14:415-435] 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. [Nordhaus (2007), Energy Economics, 29:349-372] The initial response of the IPCC was dismissive, and the PPP v MER debate rapidly turned rancorous. [Economist (Feb 13, 2003) Hot Potato: The IPCC had better check its calculations, ] [Economist (Nov 6, 2003) Hot Potato Revisited: A lack-of-progress report on the IPCC] [Economist (May 27, 2004) Measuring Economies: Garbage In, Garbage Out]
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 [Gruebler et al. (2004), Energy and Environment, 15:11-24] , some say this is only partial [Holtsmark and Alfsen (2005), Climatic Change, 68:11-19] . Overall, the effect of a switch from MER to PPP is likely to have a minimal effect on carbon dioxide concentrations in the atmosphere. [Manne et al. (2005), Climatic Change, 71:1-8]
But even if global climate change is not affected, it has been argued [ [http://ideas.repec.org/p/sgc/wpaper/45.html Tol (2006), Climatic Change, 75:59-80] ] 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.
References
External links
* [http://www.grida.no/climate/ipcc/emission/ Report website]
* [http://www.grida.no/climate/ipcc/emission/146.htm Terms of reference]
* [http://www.manicore.com/anglais/documentation_a/greenhouse/emission_scenario.html "What is an emission scenario?"] by Jean-Marc Jancovici
