East Asian Climate Response And Its Mechanism Under The Background Of Global Warming Of 1.5 And 2°C Based On The CESM Model

Utilizing high-quality NCAR(National Center for Atmospheric Research)CESM(Community Earth System Model)multi-ensemble simulations based on transient and stabilization scenarios,we investigate the responses of East Asia climate under low-warming targets(1.5? and 2?)comprehensively,including the East Asian summer monsoon,terrestrial temperature and precipitation extremes,and marine heatwaves.Further,we compare the responses between 2? and 1.5? of global warming to find out whether the extra 0.5? would lead to significant changes in the East Asian region.When the stabilization simulations are more consistent with the requirements of the Paris Agreement,transient simulations are more frequently applied in related researches.Thus,we also compare the responses between two types of scenarios.More analysis is carried out to reveal the response mechanisms of East Asian summer monsoon,terrestrial temperature and precipitation extremes,and marine heatwaves under low-warming targets.We also reveal the distinctive features in transient and stabilization responses.Major conclusions are shown below:(1)Under low-warming targets,the East Asian summer monsoon precipitation has a significant increase,while the East Asian summer monsoon circulation shows little difference.The southern part of East Asia is the key region of the summer monsoon precipitation response,where displays the largest rainfall increase.The key region also experiences a significant rise in precipitation during the extra 0.5? of global warming.More surprisingly,the precipitation difference between stabilization and transient simulations is even larger than that between 2? and 1.5? in the key region.According to the analysis of moisture budget,coastal areas exhibit strong rises in low-level water vapor and thermal effect,and thus is likely to have more rainfall.Besides the thermal effect,the dynamic effect and transient eddy effect would distinguish the precipitation response patterns between two types of simulations.The East Asian subtropical jet stream is responsible for the changes of dynamic effect and transient eddy effect by modulating the upward motion and weather-scale disturbances.Especially,the transient eddy effect has a substantial increase in the stabilization response than that in the transient response.As greenhouse gas emissions are quite different in two types of simulations,upper-level atmosphere reveals different maximum warming location and that lead to the different changes of East Asian subtropical jet stream.Moreover,the increase of latent heat in the Tibetan Plateau also has a close relationship with the transient response in East Asia.(2)Under low-warming targets,most extreme temperature and precipitation indices show significant responses in East Asia.TXx(maximum Tmax)and TNn(minimum Tmin)indices display a uniform increase in the East Asian region.SU25(Summer days)index rises more in low latitudes,while FD0(Frost days)declines more in middle and high latitudes.The most extreme situations of high temperature related TXx and SU25 indices,which have a return period of 20 years in the historical reference period,would be more frequent.On the other hand,most extreme situations of low temperature related TNn and FD0 indices may not happen in low-warming targets.Changes in extreme temperature indices are very sensitive to the extra 0.5? warming.Apart from CDD(Consecutive dry days)index,the other three extreme precipitation indices,i.e.SDII(Simple daily intensity index),R10(Number of heavy precipitation days)and R95p(Very wet days)indices,all have significant increases in the East Asian region.Also,SDII,R10 and R95 p would rise significantly in southern China during the extra 0.5? warming.While area-mean temperature extreme indices show little difference between stabilization and transient simulations,SDII,R10 and R95 p indices reveal significant positive differences in southern China.The change of mean temperature in East Asia induced by greenhouse gas emissions plays the leading role in driving the growth of extreme temperature indices.For extreme precipitation indices,the mean value and variability of precipitation exert their influences simultaneously.The East Asian summer monsoon precipitation may be responsible for the mean increase of precipitation largely in East Asia.The increase of precipitation variability may attribute to the rise of mean upward motion in southern China.Evolutions of extreme indices in East Asia are quite different from that in middle Asia,and display unique characters,such as gentle,continuous and low uncertainty.(3)Under low-warming targets,the ocean,adjacent to East Asia,shows significant increases in all marine heatwave characters.Marine heatwave intensity is stronger along the coast in the middle and high latitudes of East Asia than the other area.Marine heatwave duration and total days show more responses in low latitudes.The cumulative temperature of marine heatwave has the features of intensity and duration both.Extra 0.5? warming direct influence on all characters of the marine heatwave.Positive differences are revealed in the East China Sea and regions offshore about 30°N between the two types of simulations.The rise in mean SST dominates the upward trends of all marine heatwave characters.When the intensity of marine heatwave follows a similar pattern of mean SST change,duration and total days are more sensitive to mean SST change in low latitudes because of the narrow spread of SST distribution.The fast and slow SST responses are clearly observed in the ocean adjacent to East Asia.In transient simulations,fast STT responses dominate the change of SST;net surface flux forces the upper ocean warming;and ocean warming is faster in the upper ocean than in sub-surface.In stabilization responses,greenhouse gas emissions decline;net surface flux weakens;the sub-surface ocean keeps fast warming;slow SST responses emerge gradually;and thus SST could remain warm or even become warmer.In general,the climate in East Asia has significant responses under low-warming targets.When we compare 2? with 1.5? goals,many differences in climate responses are unveiled,and the intensity and frequency of climate extremes show obvious increases.Climate extremes in land and ocean are both very sensitive to the change of GMST.However,significant differences are disclosed in the East Asian summer monsoon rainfall and precipitation extremes between stabilization and transient responses.This indicates that many research with transient simulations may underestimate the responses of mean and extreme precipitation to a great extent.