考研阅读精选：北极气候的变化--不应打退堂鼓
『北极海冰的融化速度比气候模拟所预测的更快。这是为什么呢？』Climate change in the Arctic：beating a retreat
北极气候的变化：不应打退堂鼓
Sep 24th 2011| from the Economist
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That Arctic sea ice is disappearing has been known for decades. Theunderlying cause is believed by all but a handful of climatologists tobe global warming brought about by greenhouse-gas emissions. Yet therate the ice is vanishing confounds these climatologists’ models. Thesepredict that if the level of carbon dioxide, methane and so on in theatmosphere continues to rise, then the Arctic Ocean will be free offloating summer ice by the end of the century. At current rates ofshrinkage, by contrast, this looks likely to happen some time between2020 and 2050.
The reason is that Arctic air is warmingtwice as fast as the atmosphere as a whole. Some of the causes of thisare understood, but some are not. The darkness of land and watercompared with the reflectiveness of snow and ice means that when thelatter melt to reveal the former, the area exposed absorbs more heatfrom the sun and reflects less of it back into space. The result is afeedback loop that accelerates local warming. Such feedback, though,does not completely explain what is happening. Hence the search forother things that might assist the ice’s rapid disappearance.
One is physical change in the ice itself. Formerly a solid mass thatmelted and refroze at its edges, it is now thinner, more fractured, andso more liable to melt. But that is (literally and figuratively) amarginal effect. Filling the gap between model and reality may needsomething besides this.
The latest candidates are“short-term climate forcings”. These are pollutants, particularly ozoneand soot, that do not hang around in the atmosphere as carbon dioxidedoes, but have to be renewed continually if they are to have a lastingeffect. If they are so renewed, though, their impact may be as big asCO2’s.
At the moment, most eyes are on soot (or “blackcarbon”, as jargon-loving researchers refer to it). In the Arctic, sootis a double whammy. First, when released into the air as a result ofincomplete combustion (from sources as varied as badly serviced dieselengines and forest fires), soot particles absorb sunlight, and so warmup the atmosphere. Then, when snow or rain wash them onto an ice floe,they darken its surface and thus cause it to melt faster.
Reducing soot (and also ozone, an industrial pollutant that acts as agreenhouse gas) would not stop the summer sea ice disappearing, but itmight delay the process by a decade or two. According to a recent reportby the United Nations Environment Programme, reducing black carbon andozone in the lower part of the atmosphere, especially in the Arcticcountries of America, Canada, Russia and Scandinavia, could cut warmingin the Arctic by two-thirds over the next three decades. Indeed, thereport suggests, if such measures—preventing crop burning and forestfires, cleaning up diesel engines and wood stoves, and so on—wereadopted everywhere they could halve the wider rate of warming by 2050.
Without corresponding measures to cut CO2 emissions, this would bebut a temporary fix. Nonetheless, it is an attractive idea because itwould have other benefits (soot is bad for people’s lungs) and would notrequire the wholesale rejigging of energy production which reducing CO2emissions implies. Not everyone agrees it would work, though. GunnarMyhre of the Centre for International Climate and Environmental Researchin Oslo, for example, notes that the amount of black carbon in theArctic is small and has been falling in recent decades. He does notbelieve it is the missing factor in the models.
The rapidmelting of the Arctic sea ice, then, illuminates the difficulty ofmodelling the climate—but not in a way that brings much comfort to thosewho hope that fears about the future climate might prove exaggerated.When reality is changing faster than theory suggests it should, acertain amount of nervousness is a reasonable response. (660 words)
文章地址：http://www.economist.com/node/21530079
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