北極融化可能耗費全球60萬億美元

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 effects 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 reforms 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's 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's 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.據《衛報》7月24日報道，一組經濟學家和極地科學家表示，北極迅速融化可能引發災難性的“經濟定時炸彈”。這個定時炸彈可能會耗費全球幾百萬億美元，破壞全球金融系統。

政府和工業界預估過去二十年範圍不斷擴張的北極圈氣候變暖可能促進經濟發展，因爲這使天然氣和油田得以開發，加快歐洲與亞洲間海運的速度。但是，研究人員首次提出北極融化能造成經濟損失的具體數額。東西伯利亞海下北極永久凍土融化後，每大規模釋放一次甲烷氣體，就可能帶來全球60萬億美元（約368萬億元）的損失。

他們表示，北極永久凍土和近岸區封存的大量甲烷中僅有一小部分緩慢釋放出來也可能觸發災難性的氣候變化和導致嚴重經濟損失。

北極海冰每年以史無前例的速度大量融化和重組。2012年9月中旬，北極海冰面積縮小至350萬平方公里，僅僅是20世紀70年代時總面積的40%。由於海冰自身不斷變薄，一些科學家估計2020年，北極海大多數夏季冰將不復存在。

越來越讓人恐懼的是，海冰面積縮減，海水變暖將使近岸區的永久凍土釋放更大量甲烷。研究人員稱，東西伯利亞北極大陸架（ESAS）以天然氣水合物形式儲存的大量溫室氣體也可能因此而釋放，也許需要50年時間慢慢釋放，又或者災難性地在很短時間內全部釋放出來。

北極對海洋和氣候等地球系統至關重要。北極發生變化，冰塊融化，全球多地將受到影響。彼得·瓦德漢姆教授（Prof Peter Wadhams）說：“北極圈夏季海冰迅速消失，將加速氣候變化和促進近岸區甲烷釋放，現在，甲烷氣體使得夏季氣溫越來越高。” 彼得·瓦德漢姆教授是劍橋大學極地海洋地理工作組的負責人，也是《自然》一篇論文的作者之一。

他說：“大量甲烷氣體會影響全球經濟和社會。發展中國家將承受大部分惡果，包括極端氣候和洪災，人類健康和農業生產也會受到影響。”

根據論文作者運用斯特恩報告（Stern review）方法計算的數據，從經濟方面來看，非洲、亞洲和南美洲相對貧困的經濟體將承擔80% 的影響。作者寫道：“額外釋放的甲烷將帶來低海拔地區洪水、極端熱應力、乾旱和風暴問題。”他們認爲，全球經濟主體尚未考慮冰川快速融化的風險，至今僅發現石油泄漏是北極變暖導致經濟下滑的可能風險。

但是，作者認爲，經濟學家遺漏了關鍵的問題。鹿特丹管理學院、論文另一作者蓋爾·懷特曼教授（Prof Gail Whiteman）稱：“世界經濟論壇（World Economic Forum）和國際貨幣基金組織（International Monetary Fund）最近都沒有意識到北極變化對經濟的危害。（他們必須）更加關注這枚可視的定時炸彈。2012年，（甲烷大量釋放）使世界經濟花費70萬億美元（約429萬億元）處理其帶來的各種問題。”

2013年後半年，全球大量海運船隻準備穿過俄羅斯北部北冰洋海域，數量之多，將創下紀錄，此舉使得亞洲和歐洲之間的航運距離縮減超過35%，成本降低40%。

據俄羅斯當局稱，至今，來自韓國、中國、日本、挪威、德國等地共計218艘船隻已經遞交今年行駛“北海航線”（NSR）的申請。這條航線會經過介於西伯利亞和阿拉斯加之間的白令海峽（Bering Strait），破冰船每年會對這條航線進行破冰，該航線每年僅開放幾個月。

但是根據2012年北極冰海面積縮減的記錄，海運公司越來越有信心使用這條航線。2011年，僅有4艘船隻完成從大西洋到太平洋全程，2012年，有46艘船隻完成全程。如果中型散裝貨船行駛這條航線，航行時間可以縮短10至15天，也可以在挪威和中國之間節省幾百噸燃料。

坐落於美國科羅拉多州博爾德的美國國家冰雪數據中心（US National snow and ice data centre）本週衛星數據顯示，融冰不斷加快，2013年初至7月24日，北極冰融化面積達到820萬平方公里（320萬平方英里），相當於去年全年的冰融化面積。7月1日至15日間，超過13萬平方公里海冰融化。發言人稱：“7月15日海冰範圍是106萬平方公里（409,000平方英里），低於1981年至2010年的平均值。”