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

游客2024-05-22  53
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] Why does Bill Randel say that the findings are surprising?
选项 A、The findings are completely opposite to previous findings.
B、The findings are not understandable at all.
C、Water vapor has both positive and negative effects.
D、The effect of water vapor is so significant.
答案 D
解析 根据题干中的Bill Randel和findings are surprising将本题出处定位到第七段。该段先提到Bill Randel认为这些发现“很令人意外”，然后说到他认为令人意外的是，平流层水蒸汽小小的变化(such a very little change)却能给地表气候带来如此大的影响(how big an effect)。由此可知，水蒸汽的作用如此之大才使得Bill Randel感到惊讶，故答案为[D]。此处的The findings指的是对水蒸汽作用的研究，文中未提到此前对此做过研究，因此也就不存在与之前的研究结论相反的问题，故排除[A]。第五段已用具体数字说明水蒸汽对全球变暖的影响，但具体如何影响的需进一步研究，[B]的说法过于绝对。文中未提到水蒸汽的负面影响，故排除[C]。
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