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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  30
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.
According to the passage, cooling the north Atlantic________.
选项 A、provides energy to power hurricanes
B、changes rising and falling air currents further south
C、hinders wind shear
D、reduces the pollution index
答案B
解析 根据题干可以将该题定位至第三段。第三段指出：北大西洋表面空气的冷却减少了飓风生成所需的能量，并将上升和下降气流进一步南推，增加大西洋飓风带的风切，从而切断刚刚形成的风暴。Dunstone说，通过这种方式，气溶胶排放量的变化似乎促使了北大西洋热带风暴的周期性变化，这些变化一直都被归结为海洋环流的自然变异。A选项指出北大西洋表面空气的冷却为飓风的形成提供了动力，这与第三段中北大西洋表面空气的冷却增大了风切变，而这种额外的风切变切断形成初期的风暴不符，所以不能选。B选项正确。C选项指出北大西洋表面空气的冷却阻止了风切变，这也不正确。D选项认为北大西洋表面空气的冷却降低了污染指数，这并未在文章中得到明确说明，所以也不正确。
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