Almost all MMD models simulate a robust precipitation increase in the 21st century (Supplementary Material Figures S11.29 and S11.30; Table 11.1). However, the scatter among the individual models is considerable. By the end of the 21st century, the projected change in the annual precipitation over the Antarctic continent varies from –2% to 35%, with a MMD-A1B ensemble median of 14% (Table 11.1). Similar (smaller) mean precipitation increase is found for the A2 (B1) scenario, with values of 15% (10%). The spatial pattern of the annual change is rather uniform (Supplementary Material Figure S11.30). The projected relative precipitation change shows a seasonal dependency, and is larger in winter than in summer (Supplementary Material Figure S11.29). The Tebaldi et al. (2004a) 5 to 95% confidence interval for winter is –1 to 34% and in summer –6 to 22% (Supplementary Material Table S11.2). The projected increase in precipitation over Antarctica and thus greater accumulation of snow, without substantial surface melting, will contribute negatively to sea level rise relative to the present day (see Section 10.6). It is notable that the most recent model studies of antarctic precipitation show no significant contemporary trends (Van de Berg et al., 2005; Monaghan et al., 2006; Van den Broeke et al., 2006; see Section 4.6).
The moisture transport to the continent by synoptic activity represents a large fraction of net precipitation (Noone and Simmonds, 2002; Massom et al., 2004). During summer and winter, a systematic shift towards strong cyclonic events is projected by the MMD models (see Section 10.3). In particular, the frequency of occurrence of deep cyclones in the Ross Sea to Bellingshausen Sea sector is projected to increase by 20 to 40% (63%) in summer (winter) by the middle of the 21st century (Lynch et al., 2006). Related to this, the precipitation over the sub-antarctic seas and Antarctic Peninsula is projected to increase.