Future Projections of East Asian Climate Change from Multi-AOGCM Ensembles of IPCC SRES Scenario Simulations

摘要

In this paper, future climate changes over East Asia (20-50°N, 100-145°E) are projected from multimodel ensembles (MMEs) of selected coupled atmosphere-ocean general circulation model (AOGCM) simulations based on Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES) A2 and B2 scenarios. Analyzed variables include annual and seasonal near surface temperature and precipitation over East Asia. Before projecting future climate, model performances are evaluated on the simulation of the present-day climate (1961-1990) with bias, root-mean squared error (RMSE), and the Taylor diagram analysis. The result of model evaluation shows that CSIRO Mk2, ECHAM4/OPYC3, GFDL_R30_c, and HadCM3 exhibit higher performance. In order to test the sensitivity of projection results, four MMEs are defined: simple arithmetic averages of all seven AOGCM simulations (MME7) and four skillful AOGCM simulations (MME4), and skill-weighted averages of seven AOGCM simulations based on the skill scores of the Taylor diagram (MME_S1 and MME_S2). While the weighted MMEs (MME_S1 and MME_S2) have similar performances in the present-day climate simulation to that of MME7, MME4 constructed by four skillful models reveals higher performance than the other MMEs. The overall projection results from four MMEs show that East Asia will experience warmer and wetter climate in the 21st century. The projection results are not sensitive to the MME method. Areaaveraged temperature changes for three 30-year periods of 2020s, 2050s, and 2080s simulated by MME7 A2 [B2] scenario ensembles are 1.2 [1.4], 2.5 [2.4], and 4.1°C [3.2°C] increase, and precipitation changes are 0.4 [1.4], 2.2 [2.6], and 5.0% [4.0%] increase, respectively. Spatial patterns indicate that both temperature and precipitation increases are larger over the continental area than the oceanic area, and that the areas of larger inter-model variability are in accord with those of stronger climate change. The intermodel variability (noise) in precipitation changes is as large as that of ensemble mean (signal), whereas noise is much smaller than signal in the projection of temperature changes. It is demonstrated that MME4 reduces the inter-model uncertainty about a half of MME7 in the temperature projection of the late 21st century, but not in the precipitation projection. A significant difference in projected patterns between A2 and B2 scenario ensembles (defined as a potential impact of greenhouse-gas mitigation) appears in the 2080s temperature field over the southwestern part of East Asia. However, no significant differences can be found between precipitation patterns of A2 and B2 scenario ensembles because of the dominant inter-model variability. It is also shown that the climate change over East Asia has a characteristic seasonal dependence, that is, larger increases of wintertime temperature and summertime precipitation, which implicates the possible change of the East Asian monsoon system by global warming.