Permafrost is the result of heat and moisture exchange among the earth surface processes closely related to the atmosphere,lithosphere, pedosphere,hydrosphere, and biosphere,and generally as a result of the past cold periods in the late Quaternary.The degradation of permafrost is generally indicated by rising ground temperatures and by reduced thickness and areal extent of permafrost.Concurrently, because of changes in the physical and mechanical properties of frozen soils, many infrastructures in northern and alpine regions will be affected.The degradation of permafrost can also result in profound changes in the ecological and land surface processes in the northern countries and highlands.The degradation of permafrost is a complicated process due to its spatiotemporal variability and its variable time lag after the changes in air and surface temperatures.
The research of spatiotemporal variability of permafrost degradation on the Qinghai-Tibet Plateau has been completed by the researchers from Cold and Arid Regions Environmental and Engineering Research Institute,Chinese Academy of Sciences.Based on data from six meteorological stations in the permafrost regions, 60 boreholes for long-term monitoring of permafrost temperatures, and 710 hand-dug pits and shallow boreholes on the Qinghai-Tibet Plateau (QTP), the spatiotemporal variability of permafrost degradation was closely examined in relation to the rates of changes in air, surface, and ground temperatures. The decadal averages and increases in the mean annual air temperatures (MAATs) from 1961–2010 were the largest and most persistent during the last century. MAATs rose by 1.3 °C, with an average increase rate of 0.03 °C/yr. The average of mean annual ground surface temperatures (MAGSTs) increased by 1.3 °C at an average rate of 0.03 °C/yr. The rates of changes in ground temperatures were -0.01 to 0.07 °C/yr. The rates of changes in the depths of the permafrost table were -1 to +10 cm/yr. The areal extent of permafrost on the QTP shrank from about 1.50×106 km2 in 1975 to about 1.26×106 km2 in 2006. About 60% of the shrinkage in area of permafrost occurred during the period from 1996 to 2006. Due to increasing air temperature since the late 1980s, warm (>-1 °C) permafrost has started to degrade, and the degradation has gradually expanded to the zones of transitory (-1 to -2 °C) and cold (<-2 °C) permafrost. Permafrost on the southern and southeastern plateau degrades more markedly. It is projected that the degradation of permafrost is likely to accelerate, and substantial changes in the distributive features and thermal regimes of permafrost should be anticipated. However, regarding the relationships between degrading permafrost and the degradation of rangelands, it is still too early to draw reliable conclusions due to inadequate scientific criteria and evidence.
This research was subsidized by the China Key Research Project for Global Change (No. 2010CB951404) "Changes in the Cryosphere in the Northern Hemisphere and their Impacts on Climatic Environments, and their Adaptation",and the China National Science Foundation (No.40821001) "Frozen Ground and Cold Regions Engineering".
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Distribution of permafrost in central and eastern Asia, and locations of Thermal State of Permafrost (TSP) boreholes
(revised from Marchenko et al., 2006)(image by Sciences in Cold and Arid Regions)
Introduction
