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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.
The best tide for the text may be ______.
选项 A、Climate Change: Slow in Coming
B、Jet Stream: The Cause of Climate Change
C、Climate Change: Quicker Than What We Think
D、Global Warming: More Serious Than Before
答案C
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。
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