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Why the Earth’s surface temperature hasn’t warmed as expected over the past

游客2023-09-06  54
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." [br] According to the earlier study, the Earth hasn’t warmed as expected because______.
选项 A、the amount of greenhouse gases released is quite small
B、people are not sensitive to the change of the climate
C、its climate may not be that sensitive to greenhouse gases
D、water vapor in the stratosphere has increased sharply
答案 C
解析 根据题干中earlier study和the Earth hasn’t warmed将本题出处定位到首段。该段首句指出，地球表面温度为什么没有像预期那样变暖的问题一直困扰着科学家们。第二句给出了一个早期的理论(One study out earlier)的解释：地球气候对温室气体并不如我们当前假定的那么敏感。[C]是对此解释的同义转述，故为答案。[A]在文中未提到。[B]是针对less sensitive to green-house gases设的干扰项。[D]与第四段提到的a new study的研究发现a drop．．．of water vapor in the stratosphere矛盾，且不是早期理论的解释，故排除。
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