Which of the following makes the largest contribution to the greenhouse effect in the atmosphere?

Correct answer: (a) Carbon dioxide

Explanation

Carbon dioxide contributes most to the human-caused greenhouse effect, about 60–75%. It is not the most powerful greenhouse gas molecule for molecule, but there is far more of it and it stays in the atmosphere for a very long time. It comes mainly from burning fossil fuels and from deforestation.

Nitrous oxide traps about 300 times more heat per molecule but is far less abundant. Carbon monoxide is not a direct greenhouse gas, and sulphur dioxide has a cooling effect.