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An increase of mean annual air temperature (MAAT) of about 0.2–0.4 °C on the Qinghai–Tibet Plateau as compared with the 1970s, and especially winter warming, has resulted in extensive permafrost degradation. An increase of 0.1–0.5 °C in the mean annual ground temperature (MAGT) has been observed. Discontinuous permafrost bodies and thawed nuclei have been widely detected. The lower altitudinal limit of permafrost has risen 40–80 m on the Qinghai–Tibet Plateau. The total permafrost area on the Plateau has shrunk about 105 km2. Permafrost degradation has caused environmental deterioration, including the destabilization of buildings, impacted upon cold regions hydrology and water resources, and accelerated desertification. Copyright © 2000 John Wiley & Sons, Ltd.

The difference between ground soil and air temperature (Ts-Ta) was studied by using the data of ground and air temperature of 99 stations over the Qinghai-Xizang (Tibet) Plateau from 1960 to 2000,and its spatial distribution and time changing tendency have been diagnosed by principal component analysis and power spectral analysis methods. The results show that the values of (Ts-Ta) are the maximum in June and the minimum in December. The first three loading eigenvectors, which reflect the main spatially anomalous structure of (Ts-Ta) over the Qinghai-Xizang Plateau, contain the contrary changing pattern between the northwestern and the southeastern regions, the pattern response of the sea level elevation and the geography, and the pattern response of the distribution of the permafrost. There are four patterns of time evolution including the patterns of monotonous increasing or decreasing trends, the basic stability pattern and the parabola pattern with the minimum value. (Ts-Ta) has a periodic variation about 2 years. According to the spatial distribution of the third loading eigenvectors of (Ts-Ta) over the Qinghai-Xizang Plateau in cold season, the permafrost response region and the seasonal frozen ground response region are identified.