晨读英语美文100篇四级Hotter or Colder ?
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Hotter or Colder ?
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It was once thought that air pollution
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affected only the area immediately around large cities
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with factories and/or heavy automobile traffic.
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Today, we know that although these are the areas
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with the worst air pollution,
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the problem is literally worldwide.
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On several occasions over the past decade,
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a heavy cloud of air pollution
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has covered the entire eastern half of the United States
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and led to health warnings even in rural areas
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away from any major concentration of manufacturing
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and automobile traffic.
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In fact, the climate of the entire earth
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may be affected by air pollution.
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Some scientists feel
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that the increasing concentration of carbon dioxide in the air
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resulting from the burning of fossil fuels
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(coal and oil)
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is creating a “greenhouse effect” —
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holding in heat reflected from the earth
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and raising the world’s average temperature.
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If this view is correct
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and the world’s temperature is raised only a few degrees,
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much of the polar ice cap will melt
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and cities such as New York, Boston, Miami,
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and New Orleans will be under water.
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Another view, less widely held,
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is that increasing particulate matter in the atmosphere
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is blocking sunlight and lowering the earth’s temperature —
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a result that would be equally disastrous.
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A drop of just a few degrees could create something close to new ice age
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and would make agriculture difficult
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or impossible in many of our top farming areas.
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At present we do not know for sure
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that either of these conditions will happen
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(though one recent government report
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prepared by experts in the field concluded
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that the greenhouse effect is very likely).
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Perhaps, if we are very lucky,
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the two tendencies will offset each other
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and the world’s temperature will stay about the same
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as it is now.
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