(i) The sunlight that reaches to the earth, warms both atmosphere and the earth surface. The earth's atmospheric system then radiates the heat as infra-red radiations.

(ii) Gases like `CO_2`, `CH_4`, `CFCs`, `NO_2` are strong absorbers of long-wave or infra-red radiations emitted by the surface of the earth, and warm the earth's atmosphere. This is called the green house effect because it is like the glass panel of a green house that allows sunlight to pass through and then traps the resulting heat inside the structure.

(iii) `CO_2` is the principal green house gas responsible for warming of the earth.

(iv) `CO_2` is rising into the atmosphere slowly as a result of large scale burning of fossil fuels (coal, oil etc), volcanic activities and respiration

(v) `50%` of the increase in earth's temperature is due to `CO_2`, `20%` is due to `CFCs` and remaining `30%` is due to other gases.