How is excessive content of `CO_(2)` responsible for global warming ?

Explanation

In atmosphere, the concentration of `CO_2` is constant due to `CO_2` cycle. However, when the concentration of `CO_2` in the atmosphere increases beyond a certain level due to man made activities, the excess `CO_2` absorbs heat radiated by the earth. Some of it escapes into the atmosphere while the remaining part of it is radiated back to the surface of the earth. This increases the temperature of the earth and leads to global warming. The effect is called greenhouse effect.