Relative contribution of various greenhouse gases to total global warming is
$\bullet \; CO_2 = 60 \%$$\bullet \; CH_4 = 20 \%$$\bullet \; CFC= 14 \%$$\bullet \; N_2O = 6 \%$$\Rightarrow \; $ Therefore $ {CO_2}$ and $ {CH_4}$ are the major greenhouse gases