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  3. Most scientists blame people, at least in part, for global warming. Now, some researchers say people may be partly to blame for

Most scientists blame people, at least in part, for global warming. Now, some researchers say people may be partly to blame for

admin2010-01-07  50
问题       Most scientists blame people, at least in part, for global warming. Now, some researchers say people may be partly to blame for the cooling of Antarctica as well.
      While average global temperatures have risen about one degree Fahrenheit over the past century, Antarctica over all appears to have cooled slightly in the past few decades. That has been puzzling, because the polar regions are thought to be more sensitive to warming trends than the rest of the globe. Even more puzzling, a small portion of Antarctica--the peninsula that stretches north toward South America--defies the cooling trend. It has been warming very rapidly, about five degrees over the past 50 years, 10 times the global average.
      Writing in today’ s issue of the journal Science, Dr. David Thompson, a professor of atmospheric science at Colorado State University, and Dr. Susan Solomon, a senior scientist at the National Oceanic and Atmospheric Administration in Boulder, Colo., argue that the ozone hole, which has opened up each spring over Antarctica in recent years, may help explain both contradictory trends.
      A vortex of winds continually blows around Antarctica, tending to trap cold air at the South Pole. In the new paper, Dr. Thompson and Dr. Solomon show that the winds have strengthened in the past few decades, keeping the cold air even more confined. The peninsula, which lies outside the wind vortex, escapes the cooling effect, the scientists said. They say the ozone hole may be the cause of the stronger winds.
      Close to the ground, ozone, a molecule consisting of three oxygen atoms, forms a large and unhealthy component of smog. High in the atmosphere, however, nature occurring ozone is essential for life, blocking ultraviolet rays that would fatally mangle DNA. However, fewer ozone molecules mean the atmosphere absorbs less ultraviolet radiation. Instead of warming the air, the rays bounce off the snow and ice of Antarctica and reflect back into space.
     Scientists already knew that the ozone hole had cooled the upper atmosphere. Dr. Thompson and Dr. Solomon show that the troposphere, the lowest six miles of the atmosphere, has also cooled. "It’ s a lot of food for thought in there," said Dr. John Walsh, a professor of atmospheric science at the University of Illinois and an author of a paper in Science in January that indicated Antarctica was cooling. He noted that the ozone hole was usually largest in November or December, but that the greatest cooling had been about six months later.  
The main reason for the cooling trend of Antarctica is that ______ .
选项 A、the ozone h01e forms cold air around Antarctica to cool down its temperature
B、ultraviolet radiation come down from the ozone hole bounces off and reflects back into space
C、the ozone layer absorbs many sunrays
D、the troposphere close to Antarctica has cooled much
答案A
解析 见文章最后一段开头。
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