Climate change is supposed to unfold slowly, over decades. But that is not true up in the great white north, as those attending the AAAS meeting's session on climate change in the Arctic were reminded. Temperatures there are 2°C higher than their long-term average, and the upper layers of parts of the Arctic Ocean are hotter than they have been for at least 2,000 years. Summer sea ice has been vanishing faster than even the gloomiest researchers thought likely, with some now predicting the first completely ice-free summer as soon as the 2020s. The Arctic is not, though, isolated from the rest of the world; rapid changes there could have knock-on effects elsewhere. Whether or not that is happening was a question addressed by Jennifer Francis, an atmospheric scientist at Rutgers University. It is a topical subject. Along with much of the rest of America, Chicago endured a fierce and prolonged cold snap in January, in which temperatures fell to -27°C, the lowest since 1884. Meanwhile, Brits at the conference were fleeing a country that had been soaked by the heaviest winter rains in two and a half centuries, and battered by a seemingly endless succession of Atlantic storms and gales. Campaigners in both countries have been quick to blame climate change for the rotten weather. But things are rarely so straightforward in climatology. The best Dr Francis could offer was a theory as to why a warmer Arctic might be expected to lead to wilder weather in mid-latitudes, and some tentative but suggestive evidence that this is already happening. Her idea rests on the jet stream, a powerful, persistent, high-altitude "river of air" which flows around the world from west to east, affecting the weather as it goes. The jet stream is driven in part by the temperature difference between cold Arctic air and the warmer air of middle latitudes. Because the Arctic is warming more rapidly than the rest of the planet, that difference is shrinking. This ought to produce a less potent jet stream. And a less potent jet stream is a more unpredictable one.
单选题
Pessimistic researchers foretell that ______.
【正确答案】
B
【答案解析】解析：根据题干中的“pessimistic researchers”定位到第一段最后一句。其中“pessimistic researchers”对应“gloomiest researchers”；“foretell”对应“predicting”，故答案来自predicting后面的内容。即“the first completely ice-free summer as soon as the 2020s”，该句内容对应B项ice of the Arctic may melt in summer very soon，因此答案为选项B。
单选题
What can be inferred from Paragraph 2?
【正确答案】
A
【答案解析】解析：选项A对应第二段首句：The Arctic is not, though, isolated from the rest of the world; rapid changes there could have knock-on effects elsewhere. 大意为：然而，北冰洋并不与世隔绝；北冰洋气候迅速变化可能对其他地方产生连锁效应。故该项表述是正确的。选项B显然与A表述相反，故错误。选项C中的“The whole America”错误，原文说的是“Along with much of the rest of America, Chicago…”，“the whole”显然与原文不符合，故错误。选项D中的“in history”与原文“in two and a half centuries”不符，故错误。综上所述，本题答案为选项A。
单选题
Dr Francis suggests that ______.
【正确答案】
D
【答案解析】解析：根据题干中的“Dr Francis”定位到第三段最后一句：The best Dr Francis could offer was a theory as to why a warmer Arctic might be expected to lead to wilder weather in mid-latitudes, and some tentative but suggestive evidence that this is already happening. 题干中的“suggests that”对应原文“offer…a theory”这部分内容，故答案来自之后：a warmer Arctic might be expected to lead to wilder weather in mid-latitudes，而与该句最接近的是选项D，ocean warming may result in bad weather on land。故该题答案为选项D。
单选题
We learn from the text that jet stream ______.
【正确答案】
B
【答案解析】解析：根据题干中的“jet stream”定位到第四段。选项A，is a river at high altitude(是高海拔处的一条河流)，对应第四段首句：Her idea rests on the jet stream，a powerful，persistent，high-altitude "river of air"...原文说的是“高海拔气流”，故判断该项错误。选项B对应原文首句：...jet stream...affecting the weather as it goes．可见jet stream影响了天气，即改变了气候，故该项gives rise to climate change(导致气候变化)是正确的。选项C对应该段第二句：The jet stream is driven in part by the temperature difference…原文说的是“driven by temperature difference(受到温差的驱使)”，而不是C项causes temperature difference(导致温差)，故该项错误。选项D文章未提到，故错误。综上所述，本题答案为选项B。
单选题
The best tide for the text may be ______.
【正确答案】
C
【答案解析】解析：根据文章反复出现的climate change，我们可以确定本文主题是“气候变化”，而不是“全球变暖”，故选项D可以先排除。选项B中的“Jet Stream”是最后一段提到的一个概念，该项可以作为最后一段的主旨大意，但不是全文主旨。故答案在选项A和C间，这两个答案显然相反。第一段尾句为：Summer sea ice has been vanishing faster than even the gloomiest researchers thought likely，with some now predicting the first completely ice-free summer as soon as the 2020s．第四段第三句为：Because the Arctic is warming more rapidly than the rest of the planet，that difference is shrinking。其中的“faster”，“as soon as”，“rapidly”等词都提示气候变化来得很快，故选项C为答案。