9.2.2.2. Tropical Cyclones

The annual number of tropical cyclones for the greater Caribbean over the last 100 years and for the southWest Pacific cyclone belt for the past 50 years is given in Figure 9-2c,f. In both regions, high interannual and subdecadal variations are evident with no long-term overall trend.

9.2.3. Model Projections

9.2.3.1. Temperature, Precipitation, and Evaporation

Analysis of climate model results (including results from a number of global coupled atmosphere-ocean models) suggests that global mean surface air temperatures can be expected to rise in the future. Unfortunately, current computing requirements for atmosphere-ocean GCMs (AOGCMs) virtually prohibit the modeling community from conducting simulations at fine horizontal resolution; because many of the small island states fall within a grid box of the models, they are not appropriately resolved. This constraint severely limits any ability to generate future projections of climate change for small islands. Nonetheless, because the climate of these islands is influenced by the surrounding oceans, and the oceans are expected to warm in the future (albeit at a slower rate than land masses), the small island states also are likely to experience moderate warming. Pittock et al. (1995) have made some progress toward developing climate change scenarios for the southWest Pacific.

An annual mean rise in tropical sea-surface temperature of about 1.0°C is projected by AOGCMs (with a doubling of CO₂), with no appreciable differences between the two seasons. This projection is in agreement with the analysis of Wigley and Santer (1993)-who were confident that, although the magnitude of the warming in the Caribbean is uncertain, the sign of the projection is correct. The models also suggest some differential mean warming of the eastern and western Pacific Ocean. Small reductions also are projected in mean diurnal temperature ranges.

One possible consequence of generally warmer temperatures would be an increase in evaporation in the tropics. As in other regions, however, the rates of increase in evaporation in the latitudes of small island states would not be uniform because evaporation is influenced by factors other than temperature (e.g., pressure). Thus, changes in evaporation rates would be expected to vary spatially and temporally, across and within regions.

Mean rainfall intensity is projected to increase by approximately 20-30% over the tropical oceans (the main locations of the small island states) at the time of doubling of CO₂. However, simulation experiments with combined GHG and aerosol forcings suggest that mean precipitation might decrease during summer over the Mediterranean Sea region, leading to a higher probability of dry soils in islands located in this region (i.e., Cyprus and Malta). Relatively greater increases in mean rainfall are projected for the central equatorial Pacific Ocean region (see IPCC 1996, WG I, Section 6.2).

Inter-model agreement (for equilibrium experiments, as well as for coupled model experiments) on rainfall change is variable. Agreement is poor for the western tropical Atlantic Ocean/Caribbean Sea and Mediterranean Sea regions; it is moderate for the Indian Ocean and fairly good over the Pacific Ocean region (see Maul, 1993; Whetton et al., 1996).

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