Future changes in sea surface temperature in the East Asian Marginal Seas projected by CMIP6 models

Future global-mean warming and its intermodel spreads have shown to be greater in the coupled model intercomparison project phase 6 (CMIP6) models than in the earlier generation CMIP5 models, mainly due to increases in both forcing and climate sensitivity. However, regional future changes and their intermodel difference in CMIP6 models have been less known. In this study, we assessed biases in the sea surface temperature (SST) simulated from 30 CMIP6 models and then estimated future SST changes in the near-term (2021-2040) and the mid-term(2041-2060) periods under the scenarios of the low (SSP1-2.6) and high (SSP5-8.5) emissions, by using selected eight CMIP6 models with superior performance in the East Asian Marginal Seas (EAMS). The SST changes in the EAMS are projected to be more pronounced in the mid-term compared to the near-term under global warming. SST is expected to increase by approximately 1.8°C under SSP1-2.6 and by 4.5°C under SSP5-8.5, with the largest increases occurring in the Yellow Sea, East Sea, and East China Sea. Seasonal variations are significant, with summer (August) warming projected to be about 50% greater than winter (February) warming under SSP5-8.5, primarily due to the shallowing of the summer mixed layer. Uncertainty in future SST projections is higher under SSP1-2.6 than SSP5-8.5 because of the stronger signal in the SSP5-8.5 scenario. Spatially, uncertainty is lower in the coastal areas and the Yellow Sea, but higher in the East Sea and the mixed water region (interfrontal zone) between the Kuroshio and Oyashio currents, where ocean currents contribute to greater intermodel variation. In conclusion, the projected future surface warming in the East Asian Marginal Seas (EAMS) is estimated to be approximately twice the global mean, indicating that EAMS is a climate change hotspot with a high level of vulnerability to future global warming.