Greenhouse effect is the increase in the average surface temperature of the earth due to trapping of heat radiations by green house gases like carbon dioxide ,methane ,CFC's , water vapour,etc.

description: the infrared short radiations of the sun are absorbed by the surface objects of the earth.later  the emitted infrared radiations of long wavelength are not allowed to escape to space but are instead trapped by the green house gases.thus more and more short radiations are absorbed and the long radiations remain here thus increasing the global temperature.

useful effects:
1. it maintains the surface temperature of the earth thus making it suitable for existence of life.
2.if not for the greenhouse effect the earth would have been a barren land.

ill effects:
1.too much heat on the earth's surface melts the ice at the polar regions thus introducing floods .
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