The MMD-simulated annual temperature increases at the end of the 21st century range from 1.4°C to 3.2°C with a median of 2.0°C, somewhat below the global average. Fifty percent of the models give values differing from the median by only ±0.4°C. Statistical downscaling of HadCM3 results using the A2 and B2 emission scenarios gives around a 2°C rise in temperature by the 2080s, approximately the same as the HadCM3 model. The agreement between the AOGCMs and the downscaling analysis gives a high level of confidence in the temperature simulations. The downscaling was performed with the use of the Statistical DownScaling Model (SDSM) developed by Wilby et al. (2002) as part of an Assessments of Impacts and Adaptations to Climate Change in Multiple Regions and Sectors (AIACC) Small Island States SIS06 project (http://www.aiaccproject.org). Angeles et al. (2007) also simulate an approximately 1°C rise in SST up to the 2050s using the IS92a scenario. There were no noticeable differences in monthly changes (see Supplementary Material Figure S11.31). Observations suggest that warming is ongoing (Peterson et al., 2002).
According to Table 11.1, most models project decreases in annual precipitation and a few increases, varying from –39 to +11%, with a median of –12%. Figure 11.23 shows that the annual mean decrease is spread across the entire region. In DJF, some areas of increases are noted and in JJA, the region-wide decrease is enhanced, especially in the region of the Greater Antilles, where the model consensus is also strong. Monthly changes in the Caribbean are shown in Supplementary Material Figure S11.32, which also shows that the simulations for the Caribbean have a greater spread compared to the other oceanic regions (IND, NPA and SPA in S11.32). Results from HadCM3 downscaled for the A2 and B2 emission scenarios using the SDSM also show a near-linear decrease in summer precipitation to the 2080s for a station in Jamaica. Downscaled results from the SDSM for stations in Barbados and Trinidad, however, show increases rather than decreases. Thus, there is consensus between the MMD results and the downscaled results for the Greater Antilles in JJA but not for the other islands, and also not on an annual basis. Angeles et al. (2007) also simulate decreases up to the middle of the century in the vicinity of the Greater Antilles but not in the other islands in the late rainfall season. Table 11.1 shows that the decrease in JJA has the largest signal-to-noise ratio. The decrease is in agreement with the expected drying in the subtropics discussed in Sections 9.5 and 11.1. In the multi-model analysis, most models show shift to a more positive phase of the NAO (see Section 10.3), and consensus on temperature changes in the Pacific indicates an El Niño-like pattern with higher temperatures in the eastern Pacific (see Section 10.3). These conditions are associated with drying in the Caribbean. Observed trends in precipitation are unclear. While Peterson et al. (2002) find no statistically significant trends in mean precipitation amounts from the 1950s to 2000, Neelin et al. (2006) note a modest but statistically significant summer drying trend over recent decades in the Caribbean in several observational data sets.
Figure 11.23. Precipitation changes over the Caribbean from the MMD-A1B simulations. Top row: Annual mean, DJF and JJA fractional precipitation change between 1980 to 1999 and 2080 to 2099, averaged over 21 models. Bottom row: number of models out of 21 that project increases in precipitation.