An Analysis On The Characteristics And Causes Of Climate Abrupt Changes In China On Multi-Timescale

Abrupt changes of climate state are widespread in climate change at multi-timescales.Understanding the laws and causes of abrupt climate changes at different timescales during historical period are critical in predicting and coping with future abrupt climate shifts,which then provides a scientific basis for formulating the strategic plan of sustainable development of human society and economy,reducing potential economic losses caused by the sudden changes of the climate.After validating the model performance of the Community Earth System Model(CESM),the characteristics and causes of abrupt changes in surface air temperature and precipitation on centennial timescale over the past 2000 years in China are analyzed.Eight experiments have been used,including one control experiment,four single forcing experiments,two combination forcings experiments and one all forcings experiment.Meanwhile,we also investigate the characteristics and causes of abrupt climate changes on decadal timescale during three typical epochs,including the Medieval Warm Period(MWP),the Little Ice Age(LIA)and the Present Warm Period(PWP).Firstly,the performance of model in simulating the climate over the past 2000 years are validated by comparing with instrumental,reconstructed and other simulated datasets.CESM can capture the spatial distributions of surface air temperature and precipitation successfully,and reproduce the temporal variation of the temperature during the past 2000 years.The positive correlation between surface air temperature and precipitation in China has shown in model.The durations of three typical epochs over the past 2000 are also simulated well in CESM.Secondly,the characteristics of abrupt changes in surface air temperature and precipitation at multi-timescales in China over the past 2000 years are investigated with moving t-test in all forcings experiment.On centennial timescale,the whole China and its sub-regions witnessed similar changes in temperature and precipitation over the past 2000 years.The change of temperature in China is highly correlated with its change of precipitation.The total numbers,timing,direction and magnitude of temperature abrupt changes in each region over the past 2000 years are close,and the number of temperature abrupt changes are almost equal,but the timing,magnitude and direction of precipitation abrupt changes are quite different.The biggest abrupt changes in temperature and precipitation in different parts of China happen almost simultaneously.The timing of abrupt climate changes in simulation corresponds well with that in reconstructed datasets.The total numbers,time,direction and magnitude of temperature and precipitation abrupt changes on centennial timescale are almost equal in one region,climate goes dry and cold abruptly at the same time,and goes wet and warm almost simultaneously.On decadal timescale,the variation of the temperature over the whole China coincides with that over its sub-regions,but there exist significant differences in precipitation during each typical epoch.Temperature in China fluctuates consistently with the precipitation during each typical epoch,but relations between temperature and precipitation in different regions and epochs are distinguishingly uncorrelated.During each typical epoch,the timing,direction and magnitude of temperature abrupt changes in each region are close while those of precipitation has great difference.During three typical epochs,the timing of abrupt changes in temperature over the entire China take place almost simultaneously.Different from temperature,the abrupt changes in precipitation in each region are usually unsynchronized.The timing of temperature and precipitation abruption can't match well.Thirdly,causes of abrupt climate change on decadal and centennial timescale in China over the past 2000 years are explored by comparing the precipitation and the temperature changes in eight experiments by using the optimal fingerprint method and comparing climate series directly.On centennial timescale,natural factors have significant impact on abrupt temperature changes in each region over the past 2000 years.The abrupt change of temperature is mainly dominated by solar radiation,and the abrupt change of precipitation is influenced by volcanic activity.Since the 19th century,greenhouse gases have played an important role in the temperature abrupt changes in most parts of China,as well as precipitation abrupt changes in the Northwest and the Tibetan plateau in the late 20th century.On decadal timescale,during the MWP,the abrupt change of temperature and precipitation is mainly caused by volcanic activity and solor radiation,and the precipitation abrupt change is modulated by the inner variability of the climate system.The abrupt changes of temperature and precipitation during the LIA are mainly triggered by volcanic activity.With the increase of volcanic activity,climate goes cold and dry.With the decrease of volcanic activity,climate becomes warm and wet.During the PWP,the abrupt changes of temperature are mainly excited by human activity while the abrupt changes of precipitation is affected by many external forcings.In the late 20th century,the influence of greenhouse gases on abrupt change of temperature and precipitation in many regions of China is distinct,caused the abrupt change of climate in many regions to warm and wet.