(N/A) Global warming is primarily caused by the increase in the concentration of greenhouse gases in the atmosphere,which trap heat. The relative contributions of these gases to total global warming are as follows:
$1$. Carbon dioxide $(CO_2)$: It is the most significant contributor,accounting for $60\%$ of the total global warming.
$2$. Methane $(CH_4)$: It contributes $20\%$ to the total global warming.
$3$. Chlorofluorocarbons $(CFCs)$: These contribute $14\%$ to the total global warming.
$4$. Nitrous oxide $(N_2O)$: It contributes $6\%$ to the total global warming.
These percentages illustrate that $CO_2$ is the primary driver of the greenhouse effect,followed by methane,$CFCs$,and $N_2O$.