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北极融化威胁西伯利亚冻结带 |
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| 绿色嘉陵 http://www.jialingjiang.org.cn 2008-6-25 17:02:00 来源:人民网环保频道 收藏文章到:新浪VIVI POCO网摘 天极网摘 和讯网摘 百度搜藏 Google书签 |
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受目前北极海冰融化趋势的影响，从西伯利亚延伸至阿拉斯加及加拿大的永久冻结带的消融速度很可能将加快3倍。 一项研究发现，北极海冰消融已经向内陆地区扩展了大约1000英里，影响到了原本常年冻结的地区。 海冰覆盖面积越小，反射的太阳光就越少，地面吸收的热量也就越多。“我们的研究显示，如果未来几年内海冰持续快速缩减，北极变暖以及永久冻结带融化的速度很可能都将加快。”美国国家大气研究中心的大卫·劳伦斯（David Lawrence）说。去年9月，北极海冰面积缩减到多年同期平均水平的30%多，与此同时，北极地区空气温度也比1978年至2006年间的平均值上升了2摄氏度。 永久冻结带的融化会给建在其上的公路、输油管和建筑物带来破坏威胁，还可能危及该地区的野生动植物，并可能引发封存在土壤中的温室气体逸散，使得全球变暖进一步恶化。劳伦斯和美国国家冰雪数据中心的研究人员利用计算机模型分析了海冰的缩减对气温上升和永久冻结带融化的影响。他们尤其考量了位于底层永久冻结土壤和上层季节性冻结土壤之间的居间不冻层的形成。 “由于在地壳板块压力下下降的夏季暖流比相应的冬季寒流沉潜得更深，居间不冻层得以形成，也因此居间不冻层在冬季能够不再结冰，保证土壤中的冰融化时热量在地底深处也能够流通。”研究人员在这份发表于《地球物理学通信》杂志的研究论文中写道。居间不冻层可以让热量在土壤中更快地累积起来，从而加快永久冻结带融解的速度。“综合起来，这些结果意味着海冰快速缩减和永久冻结带稳定状态之间存在联系。”研究人员说。劳伦斯说，北半球大约14%的土地含有永久冻结带，北极地区土壤所封存的碳约占全球土壤中碳总量的30%。“一个尚未解决的重要问题就是，北极生物圈的微妙平衡将如何应对如此快速的升温。”他说，“我们将看到的是，比如说，海洋腐蚀现象加速，甲烷排放增多，还是海冰持续迅速后退造成的灌木加快向苔原地区入侵呢？” 论文合作者安德鲁·斯莱特（Andrew Slater）说：“海冰的快速消失会引发整个（北极）地区都能感受到的广泛变化。” 美国宇航局的克莱尔·帕金森（Claire Parkinson）表示，永久冻结带融化的后果目前还是未知的。“它们可能很严重，既会通过释放温室气体影响气候，也会由于下面的冻土融化和不稳定导致公路和建筑物损毁而影响当地社区。”（陈丹） Arctic thaw threatens Siberian permafrost By Steve Connor, Science Editor Saturday, 14 June 2008 The permafrost belt stretching across Siberia to Alaska and Canada could start melting three times faster than expected because of the speed at which Arctic Sea ice is disappearing. A study found that the effects of sea-ice loss – which reached an all-time record last summer – extend almost 1,000 miles inland to areas where the ground is usually frozen all year round. The smaller the area of sea ice, the less sunlight is reflected and the more heat is absorbed. That means scientists expect a tripling in the rate of warming over the continental land mass surrounding the Arctic. "Our study suggests that, if sea ice continues to contract rapidly over the next several years, Arctic land warming and permafrost thaw are likely to accelerate," said David Lawrence of the US National Centre for Atmospheric Research in Boulder, Colorado. Last September, the sea ice of the Arctic shrank to more than 30 per cent of its average extent for that time of the year. Meanwhile, air temperatures over the Arctic region rose by about 2C above the long-term average for the period 1978 to 2006. Melting permafrost threatens to undermine the roads, oil pipelines and buildings that are built on the permanently frozen ground. It will also endanger the region's wildlife as well as triggering the possible release of the greenhouse gases locked in the soil, which would exacerbate global warming. Dr Lawrence and researchers at National Snow and Ice Data Centre used computer models to analyse how the loss of sea ice could influence rising air temperatures and the melting of permafrost. They looked in particular at the creation of "taliks", which are patches of unfrozen ground sandwiched between layers of permanently frozen soil lower down and a seasonally frozen patch of soil above. "Taliks form when the downwelling summer heating wave extends deeper than the corresponding winter cooling wave, thereby preventing the talik from refreezing in winter and permitting heat to accumulate at depth as soil ice melts," the scientists said in their study to be published in the journal Geophysical Research Letters. Taliks allow heat to build up more quickly in the soil which increases the rate at which permafrost is subjected to a long-term thaw. "Taken together, these results imply a link between rapid sea ice loss and permafrost health," the scientists warned. Dr Lawrence said that about a quarter of the northern hemisphere's land contains perma-frost and the Arctic region's soils are believed to hold about 30 per cent of all the carbon stored in the world's soil. "An important, unresolved question is how the delicate balance of life in the Arctic will respond to such a rapid warming," he said. "Will we see, for example, accelerated coastal erosion, or increased methane emissions, or faster shrub encroachment into tundra regions if sea ice continues to retreat rapidly·" Andrew Slater, a co-author of the study, said: "The rapid loss of sea ice can trigger widespread changes that would be felt across the region." Claire Parkinson of Nasa said the consequences of the loss of the permafrost were unknown. "They could be significant, both on the climate through release of greenhouse gases and on the local communities through damage to roads and buildings as the frozen ground underneath thaws and destabilises". 与北极融化威胁西伯利亚冻结带相关文章 |
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