How does the increase in the amount of `CO_2` in the atmosphere lead to global warming ?

Explanation

The visible and some ultraviolet radiations (which have short wavelengths) from the sun reach the earth by passing through `CO_2` present in the atmosphere and as a result, the earth becomes heated. However, when the earth becomes cool, the energy is remitted from the earth surface in the form of infrared radiations (which have longer wavelength and have a heating effect). `CO_2` does not allow these radiations to pass through itself and becomes heated by absorbing them. Some of this heat is dissipated into the atmosphere while the remaining part is radiated back to the earth. As a result, the temperature of the earth increases. In this way `CO_2` helps to maintain the temperature on the earth required for the existence of living organisms. However, if the amount of `CO_2` in the air increases due to some human activity, the temperature of the earth increases more than required. This phenomenon is called global warming.