Projected regional temperature changes in the South Pacific from a range of AOGCMs have been prepared by Lal et al. (2002), Lal (2004) and Ruosteenoja et al. (2003). Jones et al. (2000, 2002) and Whetton and Suppiah (2003) also consider patterns of change. Broadly, simulated warming in the South Pacific closely follows the global average warming rate. However, there is a tendency in many models for the warming to be a little stronger in the central equatorial Pacific (North Polynesia) and a little weaker to the south (South Polynesia).
The MMD-A1B projections for the period 2080 to 2099 show an increase in annual temperature of 1.8°C, somewhat below the global average over the South Pacific (Table 11.1). The individual model values vary from 1.4°C to 3.1°C and at least half of the models project values very close to the mean. All models show increases, slightly less in the second half of the year compared to the first (Supplementary Material Figure S11.31). Over the North Pacific, the models simulate an increase in temperature of 2.3°C, slightly below the global average, with values ranging from 1.5°C to 3.7°C and 50% of the models within ±0.4°C of the mean. All models show increases, more in the second half of the year compared to the first (Supplementary Material Figure S11.31).
For the same period, 2080 to 2099, annual precipitation increases over the southern Pacific when averaged over all MMD models are close to 3%, with individual models projecting values from –4 to +11% and 50% of the models showing increases between 3 and 6%. The time to reach a discernible signal is relatively short. (Table 11.1). Most of these increases were in the first half of the year (Supplementary Material Figure S11.32). For precipitation in the northern Pacific, an increase of 5% is found, with individual models projecting values from 0 to 19% and at least half of the models within –2 to +5% of the median. The time to reach a discernible signal is relatively long. Most of these increases were in the latter half of the year (Supplementary Material Figure S11.32). Figure 11.25 illustrates the spatial distribution of annual, DJF and JJA rainfall changes and inter-model consistency. The figure shows that the tendency for precipitation increase in the Pacific is strongest in the region of the ITCZ due to increased moisture transport described in Section 220.127.116.11. Griffiths et al. (2003) find an increasing trend from 1961 to 2000 in mean rainfall in and northeast of the SPCZ in the southern Pacific. As for the Indian Ocean, there is some level of confidence in the precipitation results for the Pacific, but not as high as for the temperature results.
Figure 11.25. As for Figure 11.23 but for the northern and southern Pacific Ocean.
Changes in rainfall variability in the South Pacific were analysed by Jones et al. (2000) using IPCC (1996) scenarios, but more recent simulations have not been examined. These changes will be strongly driven by changes in ENSO, and this is not well understood (see Section 10.3).