摘要
永久冻土地区大约占据整个北半球陆地表面的25%,占据俄罗斯整个陆地表面的60%以上。最近几十年,在许多地方观测到了永久冻土的变暖、融化和消退现象,这些现象可能随着气候的变化在未来出现加速的趋势。永久冻土的变化对北部大陆的自然体系、人类以及经济具有重要的意义。数学模型的结果表明,到21世纪中期,北半球近表层的永久冻土将缩小15%～30%。这将导致上面几米冻土土地的完全融化,同时,其他地区季节性融化的平均深度也将增加15%～25%,最北部位置将增加50%或者更多。这些变化将改变苔原地带碳吸收和释放的平衡,以及加速温室气体从富碳的北极湿地释放出来。永久冻土的融化对建筑在其上面的基础设施结构的影响已经引起了公众的严重关注。气候原因引起的永久冻土特性的变化,对北部陆地的几乎所有建筑结构都存在着潜在的危害,并可能将其中的很多变成不可使用的建筑。永久冻土的消退和热喀斯特地形引起的地面沉降,将导致地形的戏剧性变形以及造成水文和植被的改变,并可能最终造成现有地形的变化。最近的研究表明,非气候因素,如水文和植被的改变,可能在很大程度上控制着永久冻土对气候变暖的反应。为了更好地理解和量化在日渐变化的北部环境中多种因素产生的影响,我们需要进行更多的研究。
The permafrost regions occupy about 25% of the Northern Hemisphere's terrestrial surface, and more than 60% of that of Russia.Warming,thawing,and degradation of permafrost have been observed in many locations in recent decades and are likely to accelerate in the future as a result of climatic change.Changes of permafrost have important implications for natural systems,humans,and the economy of the northern lands.Results from mathematical modeling indicate that by the mid-21st century,near-surface permafrost in the Northern Hemisphere may shrink by 15%-30%,leading to complete thawing of the frozen ground in the upper few meters,while elsewhere the depth of seasonal thawing may increase on average by 15%-25%,and by 50% or more in the northernmost locations. Such changes may shift the balance between the uptake and release of carbon in tundra and facilitate emission of greenhouse eases from the carbon-rich Arctic wetlands.Serious public concerns are associated with the effects that thawing permafrost may have on the infrastructure constructed on it.Climate-induced changes of permafrost properties are potentially detrimental to almost all structures in northern lands,and may render many of them unusable.Degradation of permafrost and ground settlement due to thermokarst may lead to dramatic distortions of terrain and to changes in hydrology and vegetation,and may lead ultimately to transformation of existing landforms.Recent studies indicate that nonclimatic factors,such as changes in vegetation and hydrology,may largely govern the response of permafrost to global warming.More studies are needed to better understand and quantify the effects of multiple factors in the changing northern environment.
