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Those atmospheric components that absorb strongly in
the infrared region of the spectrum. Infrared radiation is reflected and emitted
by the earth's surface as heat and causes a fairly large warming effect when
trapped by these gases in the atmosphere. In order of abundance and importance
as greenhouse gases are water vapor, carbon dioxide, ozone, nitrous oxide,
methane, and chlorofluorocarbons (CFCs). Absorption by water vapor, the most
common greenhouse gas, explains why many humid or cloudy days feel much hotter
than dry, clear days of the same air temperature. Because of these gases, only
about 5% of the radiation escapes from the atmosphere while more than 90% is
radiated back to the surface of the earth.
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