The increases of atmospheric carbon dioxide and other greenhouse gases have caused fundamental changes to the physical and biogeochemical properties of the oceans,and it will continue to occur in the foreseeable future.Based on the outputs of nine Earth System Models from the fifth phase of the Coupled Model Intercomparison Project (CMIP5),in this study,we provided a synoptic assessment of future changes in the sea surface temperature (SST),salinity,dissolved oxygen (DO),seawater pH,and marine net primary productivity (NPP) in the coastal China seas over the 21st century.The results show that the mid-high latitude areas of the coastal China seas (East China Seas (ECS),including the Bohai Sea,Yellow Sea,and East China Sea) will be simultaneously exposed to enhanced warming,deoxygenation,acidification,and decreasing NPP as a consequence of increasing greenhouse gas emissions.The magnitudes of the changes will increase as the greenhouse gas concentrations increase.Under the high emission scenario (Representative Concentration Pathway 8.5),the ECS will experience an SST increase of 3.24±1.23°C,a DO concentration decrease of 10.90±3.92 μmol/L (decrease of 6.3％),a pH decline of 0.36±0.02,and a NPP reduction of-17.7±6.2 mg/(m2·d) (decrease of 12.9％) relative to the current levels (1980 2005) by the end of this century.The co-occurrence of these changes and their cascade effects are expected to induce considerable biological and ecological responses,thereby making the ECS among the most vulnerable ocean areas to future climate change.Despite high uncertainties,our results have important implications for regional marine assessments.