Climate Change 2001: Working Group I: The Scientific Basis

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Introduction

Appendix II gives, in tabulated form, the values for emissions, abundances and burdens, and, radiative forcing of major greenhouse gases and aerosols based on the SRES¹ scenarios (Naki´cenovi´c et. al., 2000). The Appendix also presents global projections of changes in surface air temperature and sea level using these SRES emission scenarios.

The emission values are only anthropogenic emissions and are the ones published in Appendix VII of the SRES Report. Apart from the CO₂ emissions, for which deforestation and land use values are given in the SRES Report, the SRES scenarios for the rest of the gases define only the changes in direct anthropogenic emissions and do not specify the current magnitude of the natural emissions nor the concurrent changes in natural emissions due either to direct human activities such as land-use change or to the indirect impacts of climate change. Emissions for black carbon (BC) aerosols and organic matter carbonaceous (OC) aerosols species not covered in the SRES Report, are calculated by scaling to the SRES anthropogenic CO emissions.

The abundances and burdens for each of the species are calculated with the latest climate chemistry and climate carbon models (see Chapters 3, 4 and 5 for details).

The radiative forcings due to well-mixed greenhouse gases are computed using each of the simplified expressions given in Chapter 6, Table 6.2. The radiative forcings associated with future tropospheric O₃ increase are calculated on the basis of the O₃ changes presented in Chapter 4 for the various SRES scenarios. The mean forcing per DU estimated from the various models, and given in Chapter 6, Table 6.3 (i.e., 0.042 Wm^-2/DU), is used to derive these future forcings. For each aerosol species, the ratio of the column burdens for the particular scenario to that of the year 2000 is multiplied by the “best estimate” of the present day radiative forcing (see Chapter 6 for more details). The radiative forcings for all the species have been calculated since pre-industrial time.

The global mean surface air temperature and sea level projections, based on the SRES scenarios, have been calculated using Simple Climate models which have been “tuned” to get similar responses to the AOGCMs in the global mean (see Chapters 9 and 11 for details).

The results presented are global mean values, every ten years from 2000 to 2100, for a range of scenarios. These scenarios are the final approved Illustrative Marker Scenarios (A1B, A1T, A1FI, A2, B1, and B2); the preliminary marker scenarios (A1p, A2p, B1p, B2p, approved by the IPCC Bureau in June 1998) and, for comparison and for some species, results based on a previous scenario used by IPCC (IS92a) have also been added. For some gases, the values tabulated in the IPCC Second Assessment Report (IPCC, 1996; hereafter SAR), for that IS92a scenario using the previous generation of chemistry and climate models, are also given.