greenhouse effect

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A phenomenon in which the atmosphere of a planet traps radiation emitted by its sun, caused by gases such as carbon dioxide, water vapor, and methane that allow incoming sunlight to pass through but retain heat radiated back from the planet's surface.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun ecology (with the) The process by which a planet is warmed by its atmosphere.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun warming that results when solar radiation is trapped by the atmosphere; caused by atmospheric gases that allow sunshine to pass through but absorb heat that is radiated back from the warmed surface of the earth