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Hotter or Colder ?
It was once thought that air pollution affected only the area immediately
around large citieswith factories and/or heavy automobile traffic.
Today, we know that although these are the areas with the worst air
pollution, the problem isliterally worldwide.
On several occasions over the past decade, a heavy cloud of air pollution
has covered theentire eastern half of the United States and led to health
warnings even in rural areas awayfrom any major concentration of manufacturing
and automobile traffic.
In fact, the climate of the entire earth may be affected by air
pollution.
Some scientists feel that the increasing concentration of carbon dioxide in
the air resultingfrom the burning of fossil fuels (coal and oil) is creating a
“greenhouse effect” — holding inheat reflected from the earth and raising the
world's average temperature.
If this view is correct and the world's temperature is raised only a few
degrees, much of thepolar ice cap will melt and cities such as New York, Boston,
Miami, and New Orleans will beunder water.
Another view, less widely held, is that increasing particulate matter in
the atmosphere isblocking sunlight and lowering the earth's temperature — a
result that would be equallydisastrous.
A drop of just a few degrees could create something close to new ice age
and would makeagriculture difficult or impossible in many of our top farming
areas.
At present we do not know for sure that either of these conditions will
happen (though onerecent government report prepared by experts in the field
concluded that the greenhouseeffect is very likely).
Perhaps, if we are very lucky, the two tendencies will offset each other
and the world'stemperature will stay about the same as it is now. |
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发表于 2018-6-2 19:54:04