Working Group I: The Scientific Basis |
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11.5 Future Sea Level Changes
11.5.1 Global Average Sea Level Change 1990 to 2100
Warrick et al. (1996) made projections of thermal expansion and of loss of mass from glaciers and ice-sheets for the 21st century for the IS92 scenarios using two alternative simple climate models. Since the SAR, time-dependent experiments have been run with several AOGCMs (Chapter 9.1.2, Table 9.1) following the IS92a scenario (Leggett et al., 1992) for future concentrations of greenhouse gases, including the direct effect of sulphate aerosols. In Section 11.5.1.1, we use the AOGCM IS92a results to derive estimates of thermal expansion and land ice melt, employing methods from the literature as described in Section 11.2, and we add contributions from thawing of permafrost, sediment deposition, and the continuing adjustment of the ice sheets to climate changes since the LGM. The choice of scenario is not the principal consideration; the main point is that the AOGCMs all follow the same scenario, so the range of results reflects the systematic uncertainty inherent in the modelling of sea level changes. The use of IS92a also facilitates comparison with the result of Warrick et al. (1996). To quantify the uncertainty resulting from the uncertainty in future emissions, and to obtain results consistent with the global-average temperature change projections of Section 9.3.3, in Section 11.5.1.2 we derive projections for thermal expansion and land ice melt for the scenarios of the IPCC Special Report on Emissions Scenarios (SRES) (Nakic´enovic´ et al., 2000) (see also Box 9.1 in Chapter 9, Section 9.1). The results are given as sea level change relative to 1990 in order to facilitate comparison with previous IPCC reports, which used 1990 as their base date. 11.5.1.1 Projections for a single scenario based on a range of AOGCMsThermal expansion Continues on next page |
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