Future climate in world regions: an intercomparison of model-based projections for the new IPCC emissions scenarios

Projections of changes in seasonal surface air temperature and precipitation for three 30-year periods during the 21st century in 32 sub-continental scale regions are presented. This information may offer useful guidance on the selection of climate scenarios for regional impact studies. The climate changes have been simulated by seven coupled atmosphere-ocean general circulation models (AOGCMs), the greenhouse gas and aerosol forcing being inferred from the SRES emission scenarios A1FI, A2, B1 and B2. For a majority of the AOGCMs, simulations have only been conducted for scenarios A2 and B2. Projections for other scenarios were then extrapolated from the available runs applying a pattern-scaling technique. In tests, this method proved to be fairly accurate, the correlation between the AOGCMsimulated and the corresponding pattern-scaled response to A2 scenario for the end of the 21th century being generally ∼ 0.97− 0.99 for temperature and ∼ 0.9 or higher for precipitation. Projected changes of temperature and precipitation are presented in the form of 384 scatter diagrams. The model-simulated temperature changes were almost invariably statistically significant, i.e., they fell clearly outside the natural multi-decadal variability derived from 1000-year unforced coupled AOGCM simulations. For precipitation, fewer modelled changes were statistically significant, especially in the earliest projection period 2010-2039. Differences in the projections given by various models were substantial, of the same order of magnitude by the end of the century as differences among the responses to separate forcing scenarios. Nevertheless, the surface air temperature increased in all regions and seasons. For precipitation, changes with both sign occurred, but an increase of regional precipitation was more common than a decrease. All models simulate higher precipitation at high latitudes and enhanced summer monsoon precipitation for Southern and Eastern Asia. There was agreement between models that precipitation declines in Australia, Southern Africa and the Mediterranean region in certain seasons. The results presented on the scatter diagrams are also available in numerical form from the IPCC Data Distribution Centre.

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