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  3. Cleaning up our air may have made us healthier. A new analysis shows that the number of storms falls when pollution rises, and i

Cleaning up our air may have made us healthier. A new analysis shows that the number of storms falls when pollution rises, and i

admin2017-11-08  33
问题    Cleaning up our air may have made us healthier. A new analysis shows that the number of storms falls when pollution rises, and increases when pollution drops. Further tightening of present pollution controls " could reduce aerosols (气溶胶；悬浮颗粒) so quickly that we have record numbers of tropical storms for the next decade or two" , says Nick Dunstone of the Met Office
   Hadley Centre in Exeter, UK.
   Earlier studies found no connection between storm numbers and aerosols’ ability to cool the surface by scattering light in the open air. But aerosols also increase the brightness and lifetime of low-level marine clouds. When Nick Dunstone of the Met Office Hadley Centre in Exeter, UK, added this effect into his climate models, the simulated clouds cooled the surface more than expected. Historically, this cooling effect has been strongest in the north Atlantic.
   Cooling the north Atlantic reduces the energy available to power hurricanes. It also shifts rising and falling air currents further south, increasing wind shear in the Atlantic hurricane nursery. This extra wind shear tears nascent storms apart before they can gain strength. In this way, Dunstone says, changes in aerosol emissions appear to drive cyclical variations in north Atlantic tropical storms. These variations have long been attributed to natural variations in ocean circulation.
   Throughout the 20th century, aerosol emissions increased with industrialization and decreased in economic slumps. Tropical storms were frequent from the 1930s through to the 1950s, but rarer in the better economic times of the 1960s to mid-1990s. Then pollution controls reduced aerosol levels, and Atlantic hurricanes came roaring back, with 19 in 1995, a record 28 in 2005, and 19 in each of the past three years.
   Dunstone expects the increase to continue for another two decades. After that, global warming may begin to reduce the number of tropical storms, by warming the air and thus reducing the temperature difference between the sea surface and the atmosphere. It is not clear whether aerosols affect the intensity of storms.
Which of the following can be inferred from the passage?
选项 A、Because of global warming, the number of storm will increase.
B、It is not clear whether aerosols affect the number of storms.
C、The cooling effect has been strongest in the Atlantic.
D、The number of tropical storms is more in 1930s to the 1950s than in 1960s to mid-1990s.
答案D
解析 A选项说因为全球变暖，风暴的数量将会增加。文章最后一段第二句指出全球变暖可能开始造成热带风暴数量的减少。所以A选项不正确。B选项说气溶胶是否影响了风暴的数量仍未确定。文章开头就表述了污染指数与风暴数量的关系，也就说明了气溶胶与风暴数量的关系。最后一段的末句说，气溶胶对风暴强度的影响还未确定，不是说对其数量的影响，所以B选项可以排除。根据第二段最后一句的north Atlantic可以排除C选项。D选项可以根据第四段第二句得到验证。
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