北极融化可能耗费全球60万亿美元.

　　Rapid thawing of the Arctic could trigger a catastrophic "economic timebomb" which would cost trillions of dollars and undermine the global financial system, say a group of economists and polar scientists.

　　Governments and industry have expected the widespread warming of the Arctic region in the past 20 years to be an economic boon, allowing the exploitation of new gas and oilfields and enabling shipping to travel faster between Europe and Asia. But the release of a single giant "pulse" of methane from thawing Arctic permafrost beneath the East Siberian sea "could come with a $60tn [£39tn] global price tag", according to the researchers who have for the first time quantified the fects on the global economy.

　　Even the slow emission of a much smaller proportion of the vast quantities of methane locked up in the Arctic permafrost and offshore waters could trigger catastrophic climate change and "steep" economic losses, they say.

　　The Arctic sea ice, which largely melts and rorms each year, is declining at an unprecedented rate. In 2012, it collapsed to under 3.5m sqkm by mid September, just 40% of its usual extent in the 1970s. Because the ice is also losing its thickness, some scientists expect the Arctic ocean to be largely free of summer ice by 2020.

　　The growing fear is that as the ice retreats, the warming of the sea water will allow offshore permafrost to release ever greater quantities of methane. A giant reservoir of the greenhouse gas, in the form of gas hydrates on the East Siberian Arctic Shelf (ESAS), could be emitted, either slowly over 50 years or catastrophically fast over a shorter time frame, say the researchers.

　　The ramifications of vanishing ice will also be felt far from the poles, they say because the region is pivotal to the functioning of Earth systems, such as oceans and climate. "The imminent disappearance of the summer sea ice in the Arctic will have enormous implications for both the acceleration of climate change, and the release of methane from off-shore waters which are now able to warm up in the summer," said Prof Peter Wadhams, head of the Polar ocean physics group at Cambridge University and one of the authors of the paper published in the journal Nature.

　　"This massive methane boost will have major implications for global economies and societies. Much of those costs would be borne by developing countries in the form of extreme weather, flooding and impacts on health and agricultural production," he said.

　　According to the authors, who using the Stern review, calculated that 80% of the extra impacts by value will occur in the poorer economies of Africa, Asia and South America. "Inundation of low-lying areas, extreme heat stress, droughts and storms are all magnified by the extra methane emissions," they authors write. They argue that global economic bodies have not taken into account the risks of rapid ice melt and that the only economic downside to the warming of the Arctic they have identified so far has been the possible risk of oil spills.

　　But, they say, economists are missing the big picture. "Neither the World Economic Forum nor the International Monetary Fund currently recognise the economic danger of Arctic change. [They must] pay much more attention to this invisible time-bomb. The impacts of just one [giant "pulse" of methane] approaches the $70-tn value of the world economy in 2012", said Prof Gail Whiteman, at the Rotterdam School of Management and another author.

　　The Nature report comes as global shipping companies prepare to send a record number of vessels across the north of Russia later in 2013, slashing miles travelled between Asia and Europe by over 35% and cutting costs up to 40%.

　　According to Russian authorities, 218 ships from Korea, China, Japan, Norway, Germany and elsewhere have so far applied for permission to follow the "Northern sea route" (NSR) this year. This route uses the Bering Strait between Siberia and Alaska and is only open for a few months each year with an icebreaker.

　　But following 2012&aposs record collapse of the Arctic sea ice, shipping companies are gaining confidence to use the route. In 2012, only 46 ships sailed its entire length from the Atlantic to Pacific oceans and in 2011 only four. The route can save even medium-sized bulk carrier 10-15 days and hundreds of tonnes of bunker fuel on a journey between northern Norway and China.

　　Satellite data collated from the US National snow and ice data centre in Boulder, Colorado this week showed ice loss now accelerating and, at 8.2m sqkm (3.2m square miles) approaching the same extent as during last year&aposs record melt. Over 130,000 sqkm of sea ice melted between July 1 and 15. "Compared to the 1981 to 2010 average, ice extent on July 15 was 1.06m sqkm (409,000 square miles) below average," said a spokesman.

　　据《卫报》7月24日报道，一组经济学家和极地科学家表示，北极迅速融化可能引发灾难性的“经济定时炸弹”。这个定时炸弹可能会耗费全球几百万亿美元，破坏全球金融系统。

　　政府和工业界预估过去二十年范围不断扩张的北极圈气候变暖可能促进经济发展，因为这使天然气和油田得以开发，加快欧洲与亚洲间海运的速度。但是，研究人员首次提出北极融化能造成经济损失的具体数额。东西伯利亚海下北极永久冻土融化后，每大规模释放一次甲烷气体，就可能带来全球60万亿美元(约368万亿元)的损失。

　　他们表示，北极永久冻土和近岸区封存的大量甲烷中仅有一小部分缓慢释放出来也可能触发灾难性的气候变化和导致严重经济损失。

　　北极海冰每年以史无前例的速度大量融化和重组。2012年9月中旬，北极海冰面积缩小至350万平方公里，仅仅是20世纪70年代时总面积的40%。由于海冰自身不断变薄，一些科学家估计2020年，北极海大多数夏季冰将不复存在。

　　越来越让人恐惧的是，海冰面积缩减，海水变暖将使近岸区的永久冻土释放更大量甲烷。研究人员称，东西伯利亚北极大陆架(ESAS)以天然气水合物形式储存的大量温室气体也可能因此而释放，也许需要50年时间慢慢释放，又或者灾难性地在很短时间内全部释放出来。

　　北极对海洋和气候等地球系统至关重要。北极发生变化，冰块融化，全球多地将受到影响。彼得·瓦德汉姆教授(Prof Peter Wadhams)说：“北极圈夏季海冰迅速消失，将加速气候变化和促进近岸区甲烷释放，现在，甲烷气体使得夏季气温越来越高。” 彼得·瓦德汉姆教授是剑桥大学极地海洋地理工作组的负责人，也是《自然》一篇论文的作者之一。

　　他说：“大量甲烷气体会影响全球经济和社会。发展中国家将承受大部分恶果，包括极端气候和洪灾，人类健康和农业生产也会受到影响。”

　　根据论文作者运用斯特恩报告(Stern review)方法计算的数据，从经济方面来看，非洲、亚洲和南美洲相对贫困的经济体将承担80% 的影响。作者写道：“额外释放的甲烷将带来低海拔地区洪水、极端热应力、干旱和风暴问题。”他们认为，全球经济主体尚未考虑冰川快速融化的风险，至今仅发现石油泄漏是北极变暖导致经济下滑的可能风险。

　　但是，作者认为，经济学家遗漏了关键的问题。鹿特丹管理学院、论文另一作者盖尔·怀特曼教授(Prof Gail Whiteman)称：“世界经济论坛(World Economic Forum)和国际货币基金组织(International Monetary Fund)最近都没有意识到北极变化对经济的危害。(他们必须)更加关注这枚可视的定时炸弹。2012年，(甲烷大量释放)使世界经济花费70万亿美元(约429万亿元)处理其带来的各种问题。”

　　2013年后半年，全球大量海运船只准备穿过俄罗斯北部北冰洋海域，数量之多，将创下纪录，此举使得亚洲和欧洲之间的航运距离缩减超过35%，成本降低40%。

　　据俄罗斯当局称，至今，来自韩国、中国、日本、挪威、德国等地共计218艘船只已经递交今年行驶“北海航线”(NSR)的申请。这条航线会经过介于西伯利亚和阿拉斯加之间的白令海峡(Bering Strait)，破冰船每年会对这条航线进行破冰，该航线每年仅开放几个月。

　　但是根据2012年北极冰海面积缩减的记录，海运公司越来越有信心使用这条航线。2011年，仅有4艘船只完成从大西洋到太平洋全程，2012年，有46艘船只完成全程。如果中型散装货船行驶这条航线，航行时间可以缩短10至15天，也可以在挪威和中国之间节省几百吨燃料。

　　坐落于美国科罗拉多州博尔德的美国国家冰雪数据中心(US National snow and ice data centre)本周卫星数据显示，融冰不断加快，2013年初至7月24日，北极冰融化面积达到820万平方公里(320万平方英里)，相当于去年全年的冰融化面积。7月1日至15日间，超过13万平方公里海冰融化。发言人称：“7月15日海冰范围是106万平方公里(409,000平方英里)，低于1981年至2010年的平均值。”