When the solar radiations pass through the atmosphere and reach the earth surface,it is absorbed by it and re-emitted into the atmosphere.The solar radiations reach the earth in the form of shorter wave-length and is emitted back into the atmosphere in the form of longer wavelength. The longer wavelength radiations emitted by the earth back into the atmosphere is absorbed by the gases in the troposhere.The gases are called green house gases.When the green house gases in the troposphere absorb the radiations emitted by the earth,the air around the earth becomes warm.In fact this warmth of the earth's atmosphere is necessary for sustaining lives on it.If there were no green house gases,all the heat radiations emitted by the earth would escape into the space.As a result,the earth would be inhospitably cold and lives would not exist on it.It is, therefore,the green house effect is very important and is responsible for sustaining lives on the earth.However due to the over concentration of the green house in the troposphere caused by various human activities,the surface of the earth and the air close to it are overheated. The air close to it are overheated. The overheating of the air in the atmosphere is called global warming. The rise of global temperature about 0.3-0.7 was recorded in the last century. The rise in the global warming is due to increase of green house gases in the atmosphere.
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