关键词: 气候变化, 冻土退缩, 环境效应, 中国

Abstract: Permafrost area in China is about 2.15×10⁶km², characteristic of altitudinal permafrost. Permafrost in China can be further divided into latitudinal and altitudinal permafrost. The latter, with an areal extent of 1.73×10⁶km², can be further divided into plateau and apline permafrost. Significant permafrost degradation has occurred and is occurring in most parts of permafrost regions in China due to the combined influence of climatic warming and increasing anthropogenic activities. Permafrost in China has experienced major shifts in history, and may have disappeared except in very high mountains during the Quaternary. Accelerating fluctuations of climate and permafrost have been identified during the Holocene, and most areas of permafrost in China now are relics of cold climates, and are in rapid and extensive degradation, especially during the past 40 years. As a result of climatic warming of about 0.3～0.4℃ during the past 40 years characteristic of winter warming, extensive permafrost degradation in China has been interpreted and is expected in the future based on permafrost monitoring. This can be inferred from rising mean annual ground temperatures, deepening in thaw depths, disconnecting and disappearing of island permafrost, increasing and expansion of taliks and the burying of permafrost. In island permafrost zone, mean annual permafrost temperature has risen about 0.2～0.3℃ from 1970s to 1990s. In continuous permafrost zone, it has risen from 0.2 to 0.4℃. Thawed nuclei have fromed extensively on the edge of permafrost regions, where the permafrost table is buried as deep as 4～7m and where the seasonal freezing can only reach 2～3m. On the Qinghai Xizang Plateau, for example, the lower limit of permafrost distribution has increased gengrally from 40 to 80 m in elevation despits of the influence of local lithology, slope orientations and moisture conditions. The area of island permafrost zone has shrunk 35.6% on the Qinghai Xizang Plateau during the same period. Permafrost degradation has and will cast great influence on Chinese economy and environment in cold regions. Permafrost retreat and degradation has caused a lot of problems in cold regions engineering and environments in China, which have made it urgent to reconsider the permafrost protection principles for engineering constructions and operations, as well as environmental protection. The impact of permafrost degradation on water resources, thouth poorly understood due to lack of observation, will be very important for regional economy and environment in Asia.

Key words: Climatic change, permafrost degradation, environmental impact