Simulation Of The Evolution Of Permafrost In The Third Pole Since The Last Glacial Maximu

Since the Last Glacial Maximum(LGM),the Northern Hemisphere has experienced many severe climate fluctuations,resulting in the degradation and expansion of permafrost in the third polar region with the Qinghai-Tibet Plateau as the core.Affected by the climate warming in the past hundred years,permafrost in the third pole region shows a degradation trend,and the permafrost temperature,thickness and active layer thickness have changed significantly.Due to the lack of long-term and continuous observation data of permafrost thermal state,the quantitative study of permafrost changes in historical period is greatly limited.Many advantages of model simulation make it possible to study the changes of the third pole permafrost in a large area of historical long time series.This paper is based on the Geophysical Institute Permafrost Lab Version2(GIPL2)model,the Coupled Model Intercomparison Project Phase 6(CMIP6)and the Last Glacial Maximum Reanalysis(LGMR)analyze the change characteristics of permafrost at the centennial-scale and ten thousand years-scale in the third pole region respectively.The main conclusions are as follows:(1)At different sites in the study area,for the ground temperature at the depth of zero annual amplitude,the ground temperature error between simulation and monitoring is less than0.1℃,indicating that the model has a good ability to simulate the thermal state of permafrost in different regions of the study area.(2)From 1920 to 2019,the mean annual ground temperature simulated at each depth of Xidatan,Wudaoliang and Tanggula showed a warming trend,and the average warming rate at the depth of zero annual amplitude(15 m)was 0.07°C/10a,and the permafrost temperature at the shallow layer increased rapidly since 1980.Nevertheless,the response times of the thermal conditions to climate change varied with soil layers,among which the 30m lagged by about 20years compared to the 3m.The permafrost table decline rate of Xidatan,Wudaoliang and Tanggula observation points was not much different,with an average of 0.6 cm/a,the rise rate of the lower permafrost limit was 13.4 cm/a,4.0 cm/a and 4.0 cm/a,respectively,and the permafrost thickness decreased by 13.9 m,4.6 m and 4.7 m,respectively.There were differences in the response of permafrost to climate change at the three observation sites,and the permafrost in Xidaitan near the northern lower boundary of permafrost was relatively unstable and its response to climate change was more sensitive,while the permafrost of Wudaoliang and Tangula permafrost in the continuous permafrost area was relatively stable.(3)Since LGM,there are six main stages in the evolution of permafrost on the Third Pole region:in the late Pleistocene LGM period,the permafrost expanded strongly,reaching the maximum permafrost range the area of permafrost on the Qinghai-Tibet Plateau was 2.37×10~6km~2;During the late Pleistocene B(?)lling-Aller(?)d warming period,the permafrost area was slightly degraded;During the late Pleistocene Younger Dryas cooling period,the permafrost expanded slightly compared with the B(?)lling-Aller(?)d period.During Holocene Megathermal period,the stage of intense permafrost degradation,permafrost shrinkage to the lowest value since the LGM period,the area of permafrost on the Qinghai-Tibet Plateau was 0.84×10~6 km~2;During Holocene Little Ice Age period,the relative expansion of permafrost;During the modern warming period,permafrost is in a continuous degradation stage,and the current area of permafrost on the Qinghai-Tibet Plateau is only 1.11×10~6km~2.(4)Modern continued warming has led to the fact that the Third Pole region is experiencing the most intense and widespread permafrost degradation since Holocene Megathermal Period,and this trend is still intensifying.Under this background,the existing permafrost may degrade rapidly,showing a general degradation trend from east to west and from south to north,however,the permafrost in the hinterland of the Qinghai-Tibet Plateau and in the west,including the high-altitude areas of the Tianshan Mountains,is relatively stable due to its high altitude and low temperature,and can still exist for a long time.