Continued Warming of the Permafrost Regions Over the Northern Hemisphere Under Future Climate Change

Surface air temperatures can directly affect the thermal state of permafrost in the permafrost region of the Northern Hemisphere (PRONH). It is necessary to understand the trends in air temperatures and consider actual CMIP future scenario output instead of a linear temperature increase over different permafrost regions. In this study, air temperatures from 23 models of the sixth coupled-model intercomparison project (CMIP6) are evaluated against observational data from the PRONH. It is shown that most of the models reasonably represent the dominant characteristics of air temperature variations. Under three different future scenarios, air temperature and warming trends are examined using an optimal model ensemble. Results show that mean annual air temperature (MAAT) is higher in sporadic-permafrost and isolated-permafrost regions than in continuous-permafrost regions. MAAT warming rates were 0.10 degrees C/decade and 0.35 degrees C/decade from 1900 to 2014 and from 1980 to 2014, respectively, and were 0.09 degrees C/decade, 0.38 degrees C/decade, and 0.95 degrees C/decade from 2015 to 2100 under the low- to high-emission scenarios. Air temperature varies considerably between the high-altitude, transitional, and high-latitude permafrost regions (HLR), and warming trends are the greatest in HLR under future scenarios. Moreover, warming trends in different permafrost classes vary little from the historical values from 1900 to 2014, and with a gradual increase from isolated-permafrost regions to continuous-permafrost regions under future scenarios. The results suggested that air temperatures in the PRONH warmed approximately 1.6 times faster than global air temperatures from 1980 to 2014 and under the three future scenarios.