The Arctic: Polar Bare
北极：裸露的北极
The Arctic as it is known today is almost certainly gone
几乎可以肯定，今天人们熟知的北极已经消失
Those who doubt the power of human beings to change Earth’s climate should look to the Arctic, and shiver. There is no need to pore over records of temperatures and atmospheric carbon-dioxide concentrations. The process is starkly visible in the shrinkage of the ice that covers the Arctic ocean. In the past 30 years, the minimum coverage of summer ice has fallen by half; its volume has fallen by three-quarters. On current trends, the Arctic ocean will be largely ice-free in summer by 2040.
怀疑人类有多大能耐改变地球气候的人应该看看北极，看过之后他们会不寒而栗。不需要仔细查阅温度和大气中二氧化碳浓度的记录，仅从北冰洋上冰面的日益缩减就可以明显观察到这一变化。过去30年，夏季海冰的最小覆盖面积已经缩减了一半，体积缩小了四分之三。按照目前的趋势，到2040年夏季，北冰洋上的海冰将基本消失。
Climate-change sceptics will shrug. Some may even celebrate: an ice-free Arctic ocean promises a shortcut for shipping between the Pacific coast of Asia and the Atlantic coasts of Europe and the Americas, and the possibility of prospecting for perhaps a fifth of the planet’s undiscovered supplies of oil and natural gas. Such reactions are profoundly misguided. Never mind that the low price of oil and gas means searching for them in the Arctic is no longer worthwhile. Or that the much-vaunted sea passages are likely to carry only a trickle of trade. The right response is fear. The Arctic is not merely a bellwether of matters climatic, but an actor in them.
气候变化怀疑论者会不以为然。有些人可能还会欢呼：北冰洋如果没有了冰，亚洲太平洋沿岸与欧美大西洋沿岸之间就有了一条海运捷径，还有可能勘探到地球上五分之一的未探明油气资源。但这样的反应大错特错。且不说由于石油和天然气价格低廉，在北极开采已经不再划算，也不论被大肆吹嘘的海上通道可能只会承担极少的贸易量，正确的反应该是恐惧。北极不仅仅是气候问题的风向标，更是气候问题的作用因素。
The current period of global warming that Earth is undergoing is caused by certain gases in the atmosphere, notably carbon dioxide. These admit heat, in the form of sunlight, but block its radiation back into space, in the form of longer-wavelength infra-red. That traps heat in the air, the water and the land. More carbon dioxide equals more warming – a simple equation. Except it is not simple. A number of feedback loops complicate matters. Some dampen warming down; some speed it up. Two in the Arctic may speed it up quite a lot.
目前地球正在经历的全球变暖是由大气中的某些气体引起的，尤其是二氧化碳。这些气体容许热量以太阳光的形式透过大气层，但阻挡其以波长更长的红外线辐射到太空。这样一来热量就被留存在空气中、水里和陆地上。二氧化碳增多就等于变暖加剧，这是个简单的等式。只不过它其实并不简单。一些反馈循环让情况变得更复杂：有些抑制了变暖，有些则令其加速。北极的两大反馈循环可能让气候变暖大幅加快。
One is that seawater is much darker than ice. It absorbs heat rather than reflecting it back into space. That melts more ice, which leaves more seawater exposed, which melts more ice. And so on. This helps explain why the Arctic is warming faster than the rest of the planet. The deal on climate change made in Paris in 2015 is meant to stop Earth’s surface temperature rising by more than 2℃ above pre-industrial levels. In the unlikely event that it is fully implemented, winter temperatures over the Arctic ocean will still warm by between 5° and 9°C compared with their 1986-2005 average.
一是海水的颜色比冰深得多。海水吸收热量而不是将其反射回太空。这会融化更多冰面，让更多海水暴露出来，继而融化更多的冰，如此循环。这可以解释为什么北极比地球上其他地方变暖得更快。2015年在巴黎达成的气候变化协议旨在将地球表面温度较工业化前水平的升幅控制在2°C之内。假使这一协议真的能完全落实，比起1986年至2005年的平均水平，北冰洋的冬季温度仍会升高5°C到9°C。
The second feedback loop concerns not the water but the land. In the Arctic much of this is permafrost. That frozen soil locks up a lot of organic material. If the permafrost melts its organic contents can escape as a result of fire or decay, in the form of carbon dioxide or methane (which is a more potent greenhouse gas than CO2). This will speed up global warming directly – and the soot from the fires, when it settles on the ice, will darken it and thus speed its melting still more.
第二个反馈循环与水无关，而是有关陆地。北极的陆地表面大部分是永久冻土层，这些冻土锁住了大量的有机物。如果永久冻土融化，其中的有机物便会因起火或腐烂而以二氧化碳或甲烷的形式逸出，而甲烷是一种比二氧化碳更强的温室气体。这将直接加速全球变暖，而且起火产生的烟灰一旦落在冰上就会染黑冰面，从而让冰融化得更快。
A warming Arctic could have malevolent effects. The world’s winds are driven in large part by the temperature difference between the poles and the tropics. If the Arctic heats faster than the tropics, this difference will decrease and wind speeds will slow – as they have done, in the northern hemisphere, by between 5 and 15% in the past 30 years. Less wind might sound desirable. It is not. One consequence is erratic behaviour of the northern jet stream, a circumpolar current, the oscillations of which sometimes bring cold air south and warm air north. More exaggerated oscillations would spell blizzards and heatwaves in unexpected places at unexpected times.
北极变暖可能会有极恶劣的后果。世界上的风很大程度上是因两极和热带地区的温差而形成的。如果北极比热带地区升温更快，这一温差会减小，风速就会减慢。这种情况已经出现——过去30年来，北半球的风速减缓了5%到15%。风减少听起来也许令人向往，实则不然。后果之一就是北半球的急流发生紊乱。急流是一种环极气流，它的振荡有时会将冷空气带到南方，或将暖空气带到北方。如果急流振荡幅度过大，可能会在意想不到的时间给意想不到的地方带来暴风雪和热浪。
Ocean currents, too, may slow. The melting of Arctic ice dilutes salt water moving north from the tropics. That makes it less dense, and thus less inclined to sink for the return journey in the ocean depths. This slowing of circulation will tug at currents around the world, with effects on everything from the Indian monsoon to the pattern of El Niño in the Pacific Ocean.
洋流也可能减缓。北极冰面融化，稀释了从热带地区流向北方的海水。这导致海水密度降低，因而不易下沉至深海进行回流。这一循环放缓会拖慢全球的洋流，从印度的季风到太平洋厄尔尼诺现象的规律，一切都会因此受到影响。
The scariest possibility of all is that something happens to the ice cap covering Greenland. This contains about 10% of the world’s fresh water. If bits of it melted, or just broke free to float in the water, sea levels could rise by a lot more than today’s projection of 74cm by the end of the century. At the moment, the risk of this happening is hard to assess because data are difficult to gather. But loss of ice from Greenland is accelerating.
在可能发生的情形中，最恐怖的是覆盖格陵兰岛的冰盖发生变化。格陵兰岛包含了全球约10%的淡水，如果这里的冰盖融化一点，或者只是破裂后漂浮到海面上，那么到本世纪末海平面升高的水平将远远超过今天所预计的74厘米。目前很难评估这一情况发生的风险，因为数据太难收集。但格陵兰岛冰盖的融化正在加速。
What to do about all this is a different question. Even if the Paris agreement is stuck to scrupulously, the amount of carbon dioxide already in the atmosphere, together with that which will be added, looks bound eventually to make summer Arctic sea ice a thing of the past. Some talk of geoengineering – for example, spraying sulphates into the polar air to reflect sunlight back into space, or using salt to seed the creation of sunlight-blocking clouds. Such ideas would have unknown side-effects, but they are worth testing in pilot studies.
如何应对这一切也是个问题。即便严格执行了巴黎协定，大气中已有的二氧化碳，再加上未来将会增加的，看起来最终仍会让夏季的北冰洋海冰成为过去。有些人谈到地球工程，比方说向极地大气中喷洒硫酸盐，从而将阳光反射回太空，或是撒盐来促使水汽凝结成云，阻挡日光。这样的想法可能会有未知的副作用，不过仍值得在试点研究中测试。
The hard truth, however, is that the Arctic as it is known today is almost certainly gone. Efforts to mitigate global warming by cutting emissions remain essential. But the state of the Arctic shows that humans cannot simply undo climate change. They will have to adapt to it.
然而一个铁的事实是，几乎可以肯定，我们今天所知道的北极已不复存在。通过减排来减缓全球变暖的努力仍然至关重要，但北极的情况表明，人类并不能简单消除气候变化的影响。他们必须去适应这种变化。
下载：英文、中文版本