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  3. Why the Earth’s surface temperature hasn’t warmed as expected over the past decade continues to be a puzzle for scientists. One

Why the Earth’s surface temperature hasn’t warmed as expected over the past decade continues to be a puzzle for scientists. One

admin2012-01-27  42
问题     Why the Earth’s surface temperature hasn’t warmed as expected over the past decade continues to be a puzzle for scientists. One study out earlier this month theorized that the Earth’s climate may be less sensitive to greenhouse gases than currently assumed.
    Another surprising factor could be the amount of water vapor way up in the stratosphere (平流层), according to a new study out Thursday in the journal Science.
    Water vapor, a powerful, natural greenhouse gas that absorbs sunlight and re-emits heat, is "a wild card" of global warming, says the paper’s lead author, senior scientist Susan Solomon of the National Oceanic and Atmospheric Administration.
    In the Science paper, Solomon and her colleagues found that a drop in the concentration of water vapor in the stratosphere "very likely made substantial contributions to the flattening of the global warming trend since about 2000".
    The decline in water vapor in the stratosphere slowed the rate of surface warming by about 25%, compared to that which would have occurred due to carbon dioxide and other greenhouse gases, notes the study. Specifically, the planet should have warmed 0.25 degree F during the 2000s, but because of the influence of the water vapor, it rose just 0.18 degree F.
    Why did the water vapor decrease? "We really don’t know," says Solomon, "We don’t have enough information yet."
    The findings are "surprising", says Bill Randel, an atmospheric chemist at the National Center for Atmospheric Research, who was not part of the study. He said it was surprising how big an effect such a very little change in stratospheric water vapor has had on the surface climate.
    These fluctuations in water vapor could be part of a feedback loop. Although it’s known that water vapor in the troposphere (对流层) increases as the climate warms — and is a major climate feedback that is well simulated in global climate models — in sharp contrast, models do a poor job of simulating water vapor in the stratosphere, according to the paper.
    But Solomon points out this isn’t an indication that predictions on global warming are overstated: "This doesn’t mean there isn’t global warming," notes Solomon. "There’s no significant debate that it is warmer now than it was 100 years ago, due to anthropogenic (人造的) greenhouse gases."
    And how will this water vapor affect future global warming? "We really don’t know the answer to this," says Solomon. "If the water changes are due to the specific way the sea-surface temperature pattern looks right now, then it may well not be linked to the overall warming. It could just be a source of variability from one decade to another as the ocean pattern slowly changes. Or it could be linked to the overall warming of the tropics, in which case it could continue to ’put the brakes on’. Only time will tell, and more data."
What is said about global climate models?
选项 A、They are very useful in weather prediction.
B、They can give us all the information we need.
C、They cannot simulate everything we need to know.
D、They are particularly accurate when simulating water vapor.
答案C
解析 根据题干中的global climate models将本题出处定位到第八段末句。该句提到，尽管我们知道随着气候变暖，对流层水蒸汽会相应增加——这是一个主要的气候反馈机制，已在全球气候模型中很好地被模拟——但形成鲜明对比的是，这些模型不能有效地模拟平流层的水蒸汽。由此可知，全球气候模型不能模拟我们想知道的所有东西，故答案为[C]。文中未提到该模型能用于天气预报中，故排除[A]；[B]与文中的models do a poor job of…矛盾。文中说该模型很好地模拟了对流层的水蒸汽，但是不能有效地模拟平流层的水蒸汽，[D]的说法太笼统，故排除。
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