Interdecadal Variation And Attribution Of Climate During Early,Middle And Late Holocene

The Holocene climatic conditions are similar to the climatic conditions we are experiencing.Studying the characteristics of the interdecadal scale changes of the Holocene climate can not only reveal the natural background of modern warming,but also shed light on the role of natural and man-made factors in the process of climate evolution.Important.Based on the simulation result of TraCE-21ka(Transient Climate Evolution over the last 21,000 years)from Community Climate System Model Version 3(CCSM3),which includes all forcing run,orbital forcing run,greenhouse gases forcing fun,meltwater forcing run,and ice sheets and paleogeography forcing run.The verification of the simulation result is done first,then the Empirical orthogonal function decomposition,difference analysis,power spectrum analysis,and regression analysis methods are used to explore the interdecadal change characteristics and causes of the surface air temperature,precipitation,sea surface temperatures,wind field,and water vapor transportation field under the three periods.The results show that:1.Verification of TraCE-21 ka simulation performanceThe results of the TraCE-AF run are consistent with the spatial distribution pattern of the annual mean and annual cycle in the observed data and the spatial correlation coefficient of the two is 0.92 and 0.77,respectively.Although there are some differences between the simulation and the reconstruction and the variation trends are not all the same,the model simulation results are all within the uncertainty range of the reconstructed temperature series.In general,the simulation results of TraCE-21 ka are reliable.2.Characteristics of interdecadal climate change in the Early,Middle,and Late HoloceneBased on the simulation data of the TraCE-AF during the Holocene,the temporal variation trend,spatial distribution pattern,and temporal variation characteristics of climate elements such as surface temperature and precipitation in the early,middle and late Holocene are compared,the differences of global,the northern hemisphere and the southern hemisphere are analyzed and compared.The results show that:The temperature in the Holocene shows a fluctuating rising trend.The temperature series of the Northern Hemisphere and the global are more consistent with each other than the other comparison,and the correlation coefficient between the two series reaches 0.99.There are significant decadal cycles of global temperature in the three periods,mainly concentrated in 20-40 years,and 60-80 years.In the Middle Holocene,the overall warming occurred,but the cooling rate was larger,while in the Early and Late Holocene,the warming rate varied greatly.The precipitation in the Holocene shows a fluctuating rising trend.The temperature series of the Northern Hemisphere and the global have a good synchronization,and the correlation coefficient between the two series reaches 0.92.However,the precipitation in the northern and southern hemispheres presents a reverse change pattern.There are significant interdecadal cycles of global precipitation during the three periods,which are mainly concentrated in 20-35 years,40-60 years,and 70-90 years.The variation of precipitation during the Early and Late Holocene is smaller than that in the Middle Holocene,and the precipitation changes in South Asia and North China are synchronized during the Holocene.The interdecadal spatial distribution of precipitation during the Early,Middle and Holocene is consistent,and the Sahele-South Asia-North China rain belt shows consistent changes.The variation range of global SST in the Early Holocene was generally low,while the first mode of EOF decomposition of SST in the three periods appeared PDO-like mode.AMO-like modes exist in the second mode,and PDO-like modes exist in the middle and late Holocene.The period of PDO index in three periods mainly concentrates between 20-40 years,and 50-80 years,while the decadal period of AMO index mainly concentrates over 30 years.The variation range of 850 h Pa wind field spatial anomaly is the smallest in the Early Holocene and the largest in the Middle Holocene.The spatial anomaly distribution of the Late Holocene is basically opposite to that of the Middle Holocene.The precipitation increase/decrease distribution corresponding to the distribution of water vapor transport and divergence in the three periods can explain the precipitation distribution in the Early Holocene.The overall range of variation is the strongest in the Middle Holocene,while the range of variation in the Late Holocene is lower than that in the Middle Holocene and lower than that in the Early Holocene.3.Mechanism of interdecadal variation of precipitation during the Early,Middle,and Late HoloceneBased on the results of TraCE-21 ka all forcing and four sets of single forcing run,Empirical orthogonal function decomposition,and spatial correlation methods are used to explore the causes of the interdecadal variation of precipitation during the Early,Middle,and Late Holocene.Then,the linear regression method is used to analyze the physical mechanism of the interdecadal distribution pattern of precipitation in the three periods,the results show that:The interdecadal variation of the Early Holocene precipitation is mainly affected by TraCE-ORB,TraCE-GHG,TraCE-MWF,and TraCE-ICE.The EOF1 spatial correlation coefficient of the interdecadal precipitation in the two experiments is0.834,0.854,0.827,and-0.857.By affecting the variation of PDO,they further affects the "cyclone-anticyclone" distribution of the low-level wind field in the Northern Hemisphere and the interdecadal variation of water vapor transport,thus affecting the interdecadal variation of global precipitation.The interdecadal variation of precipitation during the Middle Holocene is mainly affected by ra CE-ORB,TraCE-GHG,TraCE-MWF,and TraCE-ICE.The spatial correlation coefficient between them and that of all forcing runs is-0.822,-0.817,-0.801,and 0.861,respectively.They affect the variation of water vapor transport by affecting the distribution of 850 h Pa wind.They affect PDO,the interdecadal distribution of global precipitation is influenced as a result.The interdecadal variation of precipitation during the Late Holocene is mainly affected by greenhouse gases,and internal variability.The spatial correlation coefficients of EOF1 between TraCE-GHG and TraCE-AF is 0.871,respectively.They affect the interdecadal variation of the global low-level wind field and water vapor transport and then affect the decadal variation of the global precipitation distribution pattern.At the same time,also affect the variation of PDO,and further affect the interdecadal variation of global precipitation.