16.3 Assumptions about future trends
16.3.1 Climate and sea-level change
16.3.1.1 Temperature and precipitation
Since the TAR, future climate change projections have been updated (Ruosteenoja et al., 2003). These analyses reaffirm previous IPCC projections that suggest a gradual warming of SSTs and a general warming trend in surface air temperature in all small-island regions and seasons (Lal et al., 2002). However, it must be cautioned that, because of scaling problems, these projections for the most part apply to open ocean surfaces and not to land surfaces. Consequently the temperature changes may well be higher than current projections.
Projected changes in seasonal surface air temperature (Table 16.1) and precipitation (Table 16.2) for the three 30-year periods (2010 to 2039, 2040 to 2069 and 2070 to 2099) relative to the baseline period 1961 to 1990, have been prepared by Ruosteenoja et al. (2003) for all the sub-continental scale regions of the world, including small islands. They used seven coupled atmosphere-ocean general circulation models (AOGCMs), the greenhouse gas and aerosol forcing being inferred from the IPCC Special Report on Emissions Scenarios (SRES; Naki?enovi? and Swart, 2000) A1FI, A2, B1 and B2 emissions scenarios.
Table 16.1. Projected increase in air temperature (°C) by region, relative to the 1961–1990 period.
| Region | 2010–2039 | 2040–2069 | 2040–2069 |
|---|
| Mediterranean | 0.60 to 2.19 | 0.81 to 3.85 | 1.20 to 7.07 |
| Caribbean | 0.48 to 1.06 | 0.79 to 2.45 | 0.94 to 4.18 |
| Indian Ocean | 0.51 to 0.98 | 0.84 to 2.10 | 1.05 to 3.77 |
| Northern Pacific | 0.49 to 1.13 | 0.81 to 2.48 | 1.00 to 4.17 |
| Southern Pacific | 0.45 to 0.82 | 0.80 to 1.79 | 0.99 to 3.11 |
Table 16.2. Projected change in precipitation (%) by region, relative to the 1961–1990 period.
| Region | 2010–2039 | 2040–2069 | 2040–2069 |
|---|
| Mediterranean | -35.6 to +55.1 | -52.6 to +38.3 | -61.0 to +6.2 |
| Caribbean | -14.2 to +13.7 | -36.3 to +34.2 | -49.3 to +28.9 |
| Indian Ocean | -5.4 to +6.0 | -6.9 to +12.4 | -9.8 to +14.7 |
| Northern Pacific | -6.3 to +9.1 | -19.2 to +21.3 | -2.7 to +25.8 |
| Southern Pacific | -3. 9 to +3.4 | -8.23 to +6.7 | -14.0 to +14.6 |
All seven models project increased surface air temperature for all regions of the small islands. The Ruosteenoja et al. (2003) projected increases all lie within previous IPCC surface air temperature projections, except for the Mediterranean Sea. The increases in surface air temperature are projected to be more or less uniform in both seasons, but for the Mediterranean Sea, warming is projected to be greater during the summer than the winter. For the South Pacific, Lal (2004) has indicated that the surface air temperature by 2100 is estimated to be at least 2.5°C more than the 1990 level. Seasonal variations of projected warming are minimal. No significant change in diurnal temperature range is likely with a rise in surface temperatures. An increase in mean temperature would be accompanied by an increase in the frequency of extreme temperatures. High-latitude regions are likely to experience greater warming, resulting in decreased sea ice extent and increased thawing of permafrost (Meehl et al., 2007).
Regarding precipitation, the range of projections is still large, and even the direction of change is not clear. The models simulate only a marginal increase or decrease (10%) in annual rainfall over most of the small islands in the South Pacific. During summer, more rainfall is projected, while an increase in daily rainfall intensity, causing more frequent heavier rainfall events, is also likely (Lal, 2004).