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Appendix 1: IPCC emissions scenarios

For ease of reference, a brief summary of the IPCC emissions scenarios is provided here, taken from Nakicenovic and Swart (2000).78 These scenarios are known as the ‘SRES scenarios’ after the name of the report, the Special Report on Emissions Scenarios.

The SRES scenarios are divided into four families, or storylines, that describe distinctly different future developments of economic growth, global population and technological change. These four families are known as ‘A1’, ‘A2’, ‘B1’ and ‘B2’. The A1 family is further subdivided into three groups (A1FI, A1T and A1B), so there are in total six scenario groups, for which so-called ‘illustrative’ emissions scenarios were developed by IPCC Working Group III in 2000. The SRES scenarios are shown schematically in Figure A1.1, and the storylines summarised in Box A1.1.

Figure A1.1: Schematic illustration of SRES scenarios.

 See figure at its full size (including text description).

Box A1.1: Storylines of SRES scenarios

The A1 scenario family describes a future world of very rapid economic growth, global population that peaks mid-century and declines thereafter, and the rapid introduction of new and more efficient technologies. A major underlying theme is convergence among regions of the globe, with a substantial reduction over time in regional differences in per capita income. The A1 family is split into three groups that describe alternative directions of technological change in the energy system: fossil intensive (A1FI), non-fossil energy sources (A1T) or a balance across all sources (A1B).

The B1 scenario family describes a convergent world with the same population trajectory as in the A1 storyline, but with rapid changes towards a service and information economy, with reductions in material intensity and the introduction of clean and resource-efficient technologies.

The A2 scenario family describes a very heterogeneous world, with the underlying theme of self-reliance and preservation of local identities. Global population increases continuously, economic development is regionally oriented, and per capita economic growth and technological change are more fragmented and slower than in the other storylines.

The B2 scenario family describes a world that emphasises local solutions to economic, social and environmental sustainability (ie, a heterogeneous world as in A2). Global population increases continuously at a rate slower than A2, with intermediate levels of economic development, and less rapid and more diverse technological change than in the B1 and A1 storylines.

The scenarios specify global annual emissions of the major greenhouse gases (carbon dioxide, methane, nitrous oxide and the HFCs) and sulphate aerosols. Figure A1.2 illustrates the carbon dioxide emissions. The lowest CO2 emissions occur under the B1 scenario, and the highest cumulative emissions over the 21st century under the A1FI scenario. The SRES scenarios do not include specific initiatives to mitigate climate change, which means that none of the scenarios explicitly assume implementation of the United Nations Framework Convention on Climate Change or the emissions targets of the Kyoto Protocol.

All the SRES emissions scenarios project ongoing increases in the atmospheric concentration of greenhouse gases over the coming century, even for those scenarios where the emissions start to decrease at some point before 2100. The projected global temperature increases from all scenarios over the next 50 to 100 years are much larger than those that have occurred over the past 1000 years. The IPCC does not promote any one SRES scenario as being more likely than any other.

Figure A1.2: Total global annual CO2 emissions from all sources (energy, industry and land-use change) from 1990 to 2100 (in gigatonnes (Gt) of carbon per year) for the four scenario families A1, A2, B1 and B2.

 See figure at its full size (including text description).


Nakicenovic N, Swart R (eds). 2000. Special Report on Emissions Scenarios. A Special Report of Working Group III of the Intergovernmental Panel on Climate Change. Cambridge University Press: Cambridge, UK and New York. 570 p. (21 May 2008)

78  Nakicenovic and Swart 2000.