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

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First, "greenhouse gases" refers to several gases recognized by scientists as enhancing the greenhouse effect.

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The warming effect caused by greenhouse gases rose 29% since 1990 and 1.4% over the last 12 months ending Dec. 31, 2010.

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Add the fact that it has little or no effect on reducing greenhouse gases, and the case for something better becomes appealing.

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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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Since both of these chemicals are more potent greenhouse gases than carbon dioxide, this effect, too, should help combat global warming.

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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.

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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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