Changes Of Geographic Isotherms And Phenology In The Offshore Area Of China Under Different Climate Scenarios

Over the recent decades,the sea surface temperature(SST)in the offshore area of China and adjacent waters(hereafter,offshore China),especially in the East China Seas(including Bohai,the Yellow Sea and the East China Sea),rises rapidly and has obvious regional climate and environmental effects.However,there are few studies on the long-term changes and environmental effects of SST in offshore China under different RCPs.In this paper,based on the observational and reanalysis data and the IPCC-CMIP5 data,the temporal and spatial variations of SST and the changes of geographic isotherms and phenology in offshore China under the global warming and different RCPs(RCP 2.6,4.5,8.5)are analyzed,respectively.Meanwhile,the changes of the East Asian Monsoon under the different RCPs and its relationship to,and possible impacts on SST in offshore China are also analyzed and discussed,too.The main conclusions are as follows:(1)SST in offshore China,especially the East China Seas,has a strong response to global warming,which may be related to the inter-decadal weakening of the East Asian Monsoon under the background of global warming : the East Asian Monsoon has displayed distinct inter-decadel variations with a weakening trend,which may have a promoting effect on the intrusion of the warm water of the Kuroshio and the ocean heat transport into the shelf of the East China Seas,so that the SST in offshore China,especially in the East China Seas,has rised significantly over the past decades.With the ocean warming in offshore China,the geographical isotherms in offshore China generally northward migrate and spring timing advances and fall delays.It suggests that the warming period between spring and fall in offshore China is prolonged and the cold period is obviously shortened.(2)Under the different RCPs,the response of SST is greatly different in offshore China and the most prominent SST changes are presented in the East China Seas.The CMIP5 projected results indicate that the SST in offshore China present a lesser changes under RCP2.6 than that in under RCP4.5,and the most under RCP8.5 run.These changes of SST in offshore China may differently influences on marine habitats.(3)With the rise of the SST in offshore China,the SST isotherm in offshore China generally northward migrate.The higher RCP scenario is,the greater the SST isotherm displacement is in the 21 st century.The distinct isotherm migration in in the western Yellow Sea and tropical waters is particularly projected.In addition,the seasonal shifts in offshore China toward earlier spring and later fall.It is also suggested that the warmer period will be prolonged and the cold period will be shortened,and the higher RCP scenario is,the longer of the warm period will be.(4)Under the different RCPs,the East Asian Monsoon,especially the East Asian Winter Monsoon,is closely related to the SST in the offshore areas of China.The East Asian Winter Monsoon shows a long-term weakening trend,and has a significant negative correlation with the SST changes in the offshore China,especially in the East China Seas.It implies that with the East Asian winter monsoon weakens,the SST in the Eastern China Sea rises;conversely,the SST in the East China Seas falls.The projected results show that the East Asian Winter Monsoon,presents more and more weakening trend from low to higher RCP scenario,i.e.,: with the stronger radiative forcing by greenhouse gases,the greater inter-decadal weakening of the East Asian Winter Monsoon appears,and it will be helpful for the intrusion of the warm water of the Kuroshio to the continental shelf of the East China Seas and the less release the air-sea heat flux from sea to the atmosphere,which may lead to a more significant warming trend in offshore China,especially in the East China Seas,as well as the more obvious changes of geographical isotherms and phenology.