Recent permafrost warming on the Qinghai‐Tibetan Plateau

Permafrost temperature monitoring through 10 boreholes up to 10.7 m depth has been conducted half‐monthly from 1996 through 2006 along the Qinghai‐Tibetan Highway. The primary results show that the long‐term mean annual permafrost temperatures at 6.0 m depth vary from −0.19°C at the Touerjiu Mountains (TM1) site to −3.43°C at Fenghuo Mountain (FH1) site, with an average of about −1.55°C from all 10 sites over the period of their records, indicating permafrost is relatively warm on the Plateau. Mean annual permafrost temperatures at 6.0 m depth have increased 0.12°C to 0.67°C with an average increase of about 0.43°C during the past decade. Over the same period, mean annual air temperatures from four National Weather Service Stations show an increase of about 0.6°C to 1.6°C, generally sufficient to account for the permafrost warming although other factors, such as changes in snow cover and soil moisture conditions, may also play important roles in permafrost warming. Increase in summer rainfall and decrease in winter snowfall may be cooling factors to the underlying soils, offsetting less degree of permafrost warming compared with the magnitude of air temperature increase. Permafrost temperatures at 6.0 m depth increased year‐around with most of the increase happened in spring and summer. Winter air temperature has increased 2.9°C to 4.2°C from 1995 through 2005, which may account for significant spring and summer permafrost warming at 6.0 m depth due to three to six month time lag. However, there were no significant trends of air temperature change in other seasons. Further investigation, especially comprehensive monitoring, is needed to better comprehend the physical processes governing the thermal regime of the active layer and permafrost on the Qinghai‐Tibetan Plateau.