Greenhouse effect from the eyes of a chemist

If I ask you what is greenhouse effect and what causes it, you will say "Sun emits heat radiation and some gases in the atmosphere traps heat. So the cause for the greenhouse effect is those gases which are carbon dioxide and water vapor. Have you ever wondered exactly how these gases are trapping the heat? or why carbon dioxide,not oxygen or nitrogen? Today I'm going to give you answers..
All the molecules are vibrating and they can vibrate in several modes such as stretching, rocking,bending etc. I know you still don't understand it. Let me explain. If we take a molecule, for an example lets take carbon dioxide. It has 2 bonds right? Two C=O bonds. These Oxygen atoms can vibrate..Lets say they are dancing.. They can dance in many ways.. both oxygens can come close to the carbon at the same time or one can come close while the other one is going away from carbon.. These dances are called molecular vibrations.

These vibrations occur when an external energy is supplied to the molecules. So we can take in this way. When an external power supply is given molecules become excited and starts dancing.. So the energy needed usually for these dances are in the infrared region of the electromagnetic spectrum.

One of the important thing is all the molecules do not dance to IR region,some dance and some do not. So how are we suppose to know which dances and which don't? It is very easy..In the scientifix terms we say, homonuclear diatomic molecules are infrared inactive and heteronuclear diatomic molecules are infrared active. Now what does that mean? In a diatomic molecule if both atoms are the same, then it will not dance to the IR energy,but why is that? For a vibration there should be a dipole moment.Which means the two atoms should not be the same. So whenever there are two similar atoms in a diatomic molecule it won't have a dipole moment.So it will not dance,and it is called IR inactive. Now you know the reason why nitrogen and oxygen can't dance. Now lets see what happens when sun emits heat radiation.

When sun emits radiation the earth absorbs it and emits it as IR waves. IR active molecules in the atmosphere such as carbon dioxide and water vapor absorbs most of this heat and starts vibrating, and some heat escapes to space. This process is what keeps our earth in a livable temperature.The concentration of water vapour in the atmosphere remained steady over time, but concentration of the carbon dioxide has been increasing since 18th century because of the industrial evolution. As a result of the increased IR active gas concentration more and more heat is trapping inside the atmosphere and temperature has started increasing. Global warming is a result of human activities and people should be more concerned about this issue since it's a threat to the survival of human beings as well as the nature.