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  3. Climate change is supposed to unfold slowly, over decades. But that is not true up in the great white north, as those attending

Climate change is supposed to unfold slowly, over decades. But that is not true up in the great white north, as those attending

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问题     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.
We learn from the text that jet stream ______.
选项 A、is a river at high altitude
B、gives rise to climate change
C、causes temperature difference
D、is to blame for global warming
答案B
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。
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