Projections of future climate change discussed in this chapter essentially are based on data sets available at IPCC Data Distribution Centers (DDCs) at Hamburg and Norwich and currently available numerical experiments with state-of-the-art global climate models that consider a near-identical GHG forcing: 1% yr-1 growth in GHG concentrations (IS92a) after 1990. Coupled AOGCMs offer the most credible tools for estimating the future response of climate to anthropogenic radiative forcings. The DDCs have compiled outputs generated in transient experiments with a set of seven recent AOGCMs that reflect the state-of-the-art of model experiments and provide a representative range of results from different AOGCMs.
A model validation exercise was undertaken for the four main regions (the Atlantic Ocean and Caribbean Sea, the Pacific Ocean, the Indian Ocean, and the Mediterranean Sea region) in which the majority of small island states are located. The results indicate that five of the seven AOGCMs [HadCM2 (UK), ECHAM4 (Germany), CSIRO (Australia), CCSR/NIES (Japan), and CCCma (Canada)] have reasonable capability in simulating the broad features of present-day climate and its variability over these regions. Comparison of the monthly mean observed and model-simulated climatology of surface air temperature and rainfall over the Mediterranean Sea and Indian Ocean regions is shown in Figures 17-2 and 17-3. The time period of 30 years (1961-1990) in baseline climatology has been used for the purpose of these model validation exercises and to generate climate change scenarios for these island regions. Two future time periods centered around the 2050s (2040-2069) and the 2080s (2070-2099) have been considered here in developing scenarios of changes in surface air temperature and precipitation.
For the four regions identified above, the HadCM2, ECHAM4, CSIRO, CCSR/NIES, and CCCma models have demonstrated good capability in simulating the present-day area-averaged monthly mean climatology in terms of surface temperature, diurnal temperature range, and rainfall (Lal I 2001). The model projections discussed here are the scenarios arising from GHG-induced positive radiative forcings and those that take into account the negative radiative forcing of sulfate aerosols (direct effects).
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