The greenhouse effect is a naturally occurring phenomenon, without which human life cannot exist on earth. It is nothing but trapping heat inside the earth’s surface. Why do we need to trap heat? Otherwise the surface of earth will not be habitable for us to stay warm and comfortable in the coldness of space.
So, how does heat get trapped? When sun’s radiation reaches our atmosphere, some is reflected back and some passes through and gets absorbed by earth. You know that energy consumption generates heat. This heat in turn excites the atoms in an object on the earth’s surface to fire off photons in infrared spectrum. Hotter the object, more infrared radiations are released by it. These outgoing infrared radiations are captured by “greenhouse gases”, keeping the planet warm.
The greenhouse gases basically act as a ‘blanket’ for infrared radiation which keeps the surface of earth warm. They reduce the ability of the earth's surface to cool, thus raising its temperature above what it would be without those greenhouse gases.
(The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface and the lower atmosphere, it results in an elevation of the average surface temperature above what it would be in the absence of the gases.)
Carbon-di-oxide (CO2), methane (CH4) and nitrous oxide (N2O) are greenhouse gases. They come from various sources and have varying trapping capabilities.
CO2 is produced by burning of the fossil fuels in vehicles, power plants, industries etc. CH4 is produced mainly from livestock, decomposing waste, agriculture. Main sources of N2O are crop fertilization, sewage treatment and burning of fossil fuels. Other greenhouse gases such as Chlorofluorocarbons are emitted in much smaller amounts by coolants in fridge, air conditioners, aerosol sprays and chemical processes.