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

游客2024-05-22  32
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] What does Solomon mean in the last paragraph?
选项 A、The connection between water vapor and global warming is not very clear yet.
B、Water,vapor is not likely to exert influence over global warming in the future.
C、The warming of the tropics plays a very important role in global warming.
D、Global warming proves to have nothing to do with the warming of the ocean.
答案 A
解析 文中末段首先提出一个问题：水蒸汽将如何影响未来的全球变暖呢?然后对此问题予以解答：“我们真的不知道这个问题的答案。”Solomon说，“……只有时间，还有更多的数据能告诉我们答案。”Solomon的言外之意就是水蒸汽与全球变暖的关系还不确定，故答案为[A]。[B]是针对文中的If the water．．．not be linked to the overall warming设的干扰项，这只是她的假设，[B]的说法过于绝对。文中说到，它可能与热带地区变暖有关，而未说热带地区变暖在全球变暧中的角色，故排除[C]。[D]的说法过于绝对。
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