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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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