These reflect sunlight away from Earth and thus oppose the effect of greenhouse gases.

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For we do know very well what is the direct effect of a doubling of greenhouse gases.

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Most of it is, of course, radiated back into space. (It is the partial blocking of this radiation by gases such as carbon dioxide that causes the much-talked-of greenhouse effect.) Some of it, however, goes in the opposite direction, into the ground.

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The WMO data, meanwhile, confirms that atmospheric concentrations of the three gases principally responsible for the man-made component of the greenhouse effect - carbon dioxide, methane, and nitrous oxide - all rose during 2009.

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Greenhouse effect: heating of the earth's atmosphere due to an increase in gases like carbon dioxide.

UNESCO: L O S S A R Y