经济学人下载:北极气候变化 仓惶撤退

Science and technology
科技报道

Climate change in the Arctic
北极气候变化

Beating a retreat
仓惶撤退

Arctic sea ice is melting far faster than climate models predict. Why?
北极海冰正在以比气候模型所预测的快得多的速度融化，为什么？

ON SEPTEMBER 9th, at the height of its summertime shrinkage, ice covered 4.33m square km, or 1.67m square miles, of the Arctic Ocean, according to America's National Snow and Ice Data Centre.
据美国国家冰雪中心监测，今年的9月9日，处于夏季收缩极值的北极海冰仅仅覆盖了433万平方公里，或相当于167万平方英里的北冰洋洋面。

That is not a record low—not quite.
这虽未创下最低记录，但也已相去不远。

But the actual record, 4.17m square km in 2007, was the product of an unusual combination of sunny days, cloudless skies and warm currents flowing up from mid-latitudes.
2007年的417万平方公里的最低记录是受到当时艳阳高照，万里无云的天空以及从中纬度上来的暖流这种异常组合的影响的产物。

This year has seen no such opposite of a perfect storm, yet the summer sea-ice minimum is a mere 4% bigger than that record.
而尽管并没有观测到如此不利的情况，今年海冰的极小值也仅仅比那年的记录大了4%。

Add in the fact that the thickness of the ice, which is much harder to measure, is estimated to have fallen by half since 1979, when satellite records began, and there is probably less ice floating on the Arctic Ocean now than at any time since a particularly warm period 8,000 years ago, soon after the last ice age.
除此以外，较难测量的冰面厚度预计比首次有卫星观测记录的1979年降低了一半。现在，漂浮在北冰洋上面的冰块很可能是8000千年前最后一个冰河期结束后的那个极暖期以来最少的。

That Arctic sea ice is disappearing has been known for decades.
数十年前，人们已经认识到北极海冰正在消亡一事。

The underlying cause is believed by all but a handful of climatologists to be global warming brought about by greenhouse-gas emissions.
除了少数人以外，几乎所有气候学家都将其归咎于温室气体排放所带来的全球变暖。

Yet the rate the ice is vanishing confounds these climatologists' models.
然而海冰消失的速率使这些气象学家建立的气候模型陷入混乱。

These predict that if the level of carbon dioxide, methane and so on in the atmosphere continues to rise, then the Arctic Ocean will be free of floating summer ice by the end of the century.
按照他们的预计，若大气中的二氧化碳、甲烷以及其他温室气体持续增加，到本世纪末夏季的北极海冰将完全消失。

At current rates of shrinkage, by contrast, this looks likely to happen some time between 2020 and 2050.
但是相较之下，依现在的消融速率，这一情况将可能在2020年到2050年之间发生。

The reason is that Arctic air is warming twice as fast as the atmosphere as a whole.
其原因是由于北极的空气正在以大气整体的两倍速度暖化。

Some of the causes of this are understood, but some are not.
其中部分根源已经被了解，但仍有一些未能解开。

The darkness of land and water compared with the reflectiveness of snow and ice means that when the latter melt to reveal the former, the area exposed absorbs more heat from the sun and reflects less of it back into space.
与强反射的冰雪表面相比，当其融化后露出下面深色的陆地或水体时，这部分区域将从太阳吸收到更多的热量而仅仅反射更少的部分到空中。

The result is a feedback loop that accelerates local warming. Such feedback, though, does not completely explain what is happening.
结果造成了一个局部暖化加速的恶性循环，尽管这种反馈机制未能完全解释当下正在发生的事情。

Hence the search for other things that might assist the ice's rapid disappearance.
今后对其他事物的研究可能会对解释海冰的快速消失带来帮助。

Forcing the issue
解决问题

One is physical change in the ice itself.
另一个原因是海冰自身的物理结构发生了改变。

Formerly a solid mass that melted and refroze at its edges, it is now thinner, more fractured, and so more liable to melt.
以前融化和冻结仅发生在冰块的边缘，但是它现在变得更薄，更易破裂，并且更倾向融化。

But that is a marginal effect. Filling the gap between model and reality may need something besides this.
但这只是名副其实的边际效应。要弥合模型与现实的差距，还需要其他原因。

The latest candidates are short-term climate forcings.
最后一个候选者是所谓的短期气候强迫物质。

These are pollutants, particularly ozone and soot, that do not hang around in the atmosphere as carbon dioxide does, but have to be renewed continually if they are to have a lasting effect.
即是大气污染物，尤其是臭氧和煤烟。尽管它们不能像二氧化碳那样在大气中停留，以至于需要不断补充以持续发挥作用。

If they are so renewed, though, their impact may be as big as CO2's.
但是假如它们得到足够的补充，将对全球变暖带来不亚于二氧化碳的影响。

At the moment, most eyes are on soot.
当前，绝大多数眼球都注目于煤烟。

In the Arctic, soot is a double whammy.
煤烟给北极带来了双重打击。

First, when released into the air as a result of incomplete combustion, soot particles absorb sunlight, and so warm up the atmosphere. Then, when snow or rain wash them onto an ice floe, they darken its surface and thus cause it to melt faster.
首先，当作为非充分燃烧的产物被排放到空中后，煤烟颗粒吸收阳光，加热了大气。其次，当雨雪将煤烟带到冰面上后，使冰面颜色变深，并导致加速消融。

Reducing soot would not stop the summer sea ice disappearing, but it might delay the process by a decade or two.
尽管减少煤烟排放不能阻止夏季海冰的消失，但或许能减缓这一过程十到二十年。

According to a recent report by the United Nations Environment Programme,
联合国环境规划署的一份最新报告显示，

reducing black carbon and ozone in the lower part of the atmosphere, especially in the Arctic countries of America, Canada, Russia and Scandinavia, could cut warming in the Arctic by two-thirds over the next three decades.
减少低层大气中的黑炭以及臭氧，尤其是北极圈国家，如美国，加拿大，俄罗斯，斯堪的纳维亚诸国，能够在未来三十年里降低北极地区的暖化速度达三分之二。

Indeed, the report suggests, if such measures—preventing crop burning and forest fires, cleaning up diesel engines and wood stoves, and so on—were adopted everywhere they could halve the wider rate of warming by 2050.
事实上，如果能如此份报告所说，到处都采取诸如防止焚烧作物和森林火灾，清理柴油发动机以及火炉等措施，到2050年止能将当下较大的暖化速率减半。

Without corresponding measures to cut CO2 emissions, this would be but a temporary fix.
如果没有相应的削减二氧化碳排放的措施，这将只是一个临时性解决方法。

Nonetheless, it is an attractive idea because it would have other benefits and would not require the wholesale rejigging of energy production which reducing CO2 emissions implies.
尽管如此，这仍是一个有足够吸引力的主意，因为它还能带来其他利益，也不会像削减二氧化碳排放那样需要大规模调整能源产业。

Not everyone agrees it would work, though. Gunnar Myhre of the Centre for International Climate and Environmental Research in Oslo, for example, notes that the amount of black carbon in the Arctic is small and has been falling in recent decades. He does not believe it is the missing factor in the models.
然而，不是每个人都认为它将很有效。例如位于奥斯陆的国际气候与环境研究中心的冈纳·迈尔表示，他注意到北极的黑炭的量微乎其微，并且已经在最近的数十年里沉降下来。他不相信这会是模型中确实的影响因子。

Carbon dioxide, in his view, is the main culprit. Black carbon deposited on the Arctic snow and ice, he says, will have only a minimal effect on its reflectivity.
在他眼中，二氧化碳才是罪魁祸首。他说，落到北极冰雪上面的黑炭，只会对其反射率带来微小的影响。

The rapid melting of the Arctic sea ice, then, illuminates the difficulty of modelling the climate—but not in a way that brings much comfort to those who hope that fears about the future climate might prove exaggerated.
北极海冰的快速消融揭示了建立气候模型的困难，只不过，与那些认为对未来气候的恐惧可能被过分夸大的人的想法背道而驰。

When reality is changing faster than theory suggests it should, a certain amount of nervousness is a reasonable response.
当事实上的变化快于纸面理论时，一定量的情绪不安是合理的反应。

It's an ill wind
一利百弊

The direct consequences of changes in the Arctic are mixed.
北极的变化将带来的各种后果。

They should not bring much rise in the sea level, since floating ice obeys Archimedes's principle and displaces its own mass of water.
它并不会使海平面上升许多，因为浮冰遵循阿基米德原理排开了相当于它自身的水。

A darker—and so more heat-absorbent—Arctic, though, will surely accelerate global warming and may thus encourage melting of the land-bound Greenland ice sheet.
然而一个相对深色的—也会吸收更多热量—北极，毫无疑问会加速全球变暖，并且可能促使连接在陆地上的格陵兰岛冰盖加快融化。

That certainly would raise sea levels.
而这将一定导致海平面上升。

Wildlife will also suffer.
野生动物也将深受其害。

Polar bears, which hunt for seals along the ice's edge, and walruses, which fish there, will both be hard-hit.
沿着浮冰边缘狩猎海豹的北极熊，以及在此捕鱼的海象，都将受到沉重打击。

The effects on the wider climate are tricky to assess.
它给更广范围的气候所带来的影响难以评估。

Some meteorologists suspect unseasonal snow storms off the east coast of America in 2010 were partly caused by Arctic warming shifting wind patterns.
一些气象学家推测北极变暖造成的气流模式改变是造成2010年袭击美国东海岸的那场非季节性暴风雪的部分原因。

One feedback loop that does seems certain, though, is that the melting Arctic will enable the extraction of more fossil fuel, with all that that implies for greenhouse-gas emissions.
然而，有一个恶性循环似乎是真的—一个融化中的北极将会使得更多化石燃料被抽取，这与温室气体排放直接关联。

The Arctic is reckoned to hold around 15% of the world's undiscovered oil reserves and 30% of those of natural gas.
北极被估计保有全球石油储量的15%以及天然气储量的30%。

Hence a growing polar enthusiasm among energy companies—as witnessed last month in an Arctic tie-up between Exxon Mobil, of America, and Rosneft, Russia's state-controlled oil giant.
因此，在能源公司中掀起了一股极地热潮—上个月美国的埃克森美孚公司与俄罗斯国有石油巨头俄罗斯石油公司达成北极大陆架战略伙伴关系协议就是明证。

Recent plankton blooms suggest a warmer Arctic will provide a boost to fisheries there, too.
而浮游生物的大量繁殖预示着一个较温暖的北极也将推动此处的渔业发展。

And the vanishing ice has begun to allow a trickle of shipping across the Arctic's generally frozen north-west and north-east passages, thus linking the Atlantic and Pacific oceans.
消失的冰面也开始允许船只缓慢通过通常封冻的北极西北和东北通道，从而连接了大西洋和太平洋。

In August a Russian supertanker, the Vladimir Tokohonov, aided by two nuclear icebreakers, became the first such vessel to cross the north-east route, hugging the Siberian coast.
在今年八月，一艘俄罗斯籍超级油轮，弗拉基米尔·蒂克霍诺夫号在两艘核能破冰船的帮助下成为了第一艘通过东北路径的同类船只。

So far, despite some posturing by Canada and Russia, there are few territorial disputes in the region and the Arctic Council, the club of Arctic nations, has functioned reasonably well.
迄今为止，除了加拿大和俄罗斯所摆出的一些姿势外，在该地区鲜少有领土争端问题。

Whether the interests of these countries coincide with those of the wider world, though, is moot.
北极理事会—北极圈国家的俱乐部，也运行良好。

A warming Arctic will bring local benefits to some.
尽管有待讨论，无论这些国家的利益是否与其他国家重合，一个正在变暖的北极只会给当地带来利益，

The rest of the world may pay the cost.
而世界上其他地方将不得不为之埋单。