单选题 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.'

单选题 According to the earlier study, the Earth hasn't warmed as expected because

【正确答案】 C

【答案解析】根据题干中earlier study和the Earth hasn't warmed将本题出处定位于第1段。第1段第1句提问，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2句给出了一个近期的理论(one study out earlier)的解释：地球气候对温室气体的反应可能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 greenhouse gases设的干扰项；D与第4段提到的一项新研究的发现相矛盾，且不是近期理论的解释，故排除。

单选题 According to Solomon and her colleagues, how does water vapor affect global temperature?

【正确答案】 A

【答案解析】根据题干中Solomon and her colleagues将本题出处定位于第4段。第4段提到，所罗门和她的同事发现，平流层中水蒸气浓度的下降“很可能对自从大约2000年起全球变暖趋势的减缓起到了实质性的作用”。这也就是说，全球变暖的减缓是因为平流层中水蒸气浓度的下降。B是针对第8段中的water vapor in the troposphere increases as the climate warms设的干扰项，文中说的是随着气候变暖，对流层水蒸气会相应增加，B是因果倒置，故排除；同时排除D“全球温度升高是因为平流层的水蒸气的增加”；文中讲的是全球变暖的速度减缓，第9段明确讲到it is warmer now，故排除C。

单选题 Why does Bill Randel say that the findings are surprising?

【正确答案】 D

【答案解析】根据题干中的Bill Randel和findings are surprising将本题出处定位于第7段。第7段先提到，比尔·兰德尔认为这些发现“很令人意外”，然后说他认为令人意外的是，平流层水蒸气小小的变化(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，水蒸气的作用如此之大使得比尔·兰德尔感到惊讶。此处的the findings指的是对水蒸气作用的研究，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5段已用具体数字说明水蒸气对全球变暖的影响，但具体如何影响需进一步研究，B的说法过于绝对；文中未提到水蒸气的负面影响，故排除C。

单选题 What is said about global climate models?

【正确答案】 C

【答案解析】根据题干中的global climate models将本题出处定位于第8段最后一句。第8段最后一句提到，尽管我们知道随着气候变暖，对流层水蒸气会相应增加——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气。由此可知，全球气候模型不能模拟我们想知道的所有东西。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气，但是不能有效地模拟平流层的水蒸气，D的说法太笼统，故排除。

单选题 What does Solomon mean in the last paragraph?

【正确答案】 A

【答案解析】根据题干将本题出处定位于最后一段。最后一段首先提出一个问题：水蒸气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，”所罗门说，“……只有时间和更多的数据能告诉我们答案。”所罗门的言外之意就是，水蒸气与全球变暖的关系还不确定。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，故排除；文中提到，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暖中的角色，故排除C；D的说法过于绝对，故排除。