Which of the following greenhouse gases is entirely anthropogenic in origin?

Chlorofluorocarbons are entirely human-made industrial chemicals with no natural source.

Water vapour is overwhelmingly natural, the most abundant greenhouse gas arising from evaporation.

Carbon dioxide has vast natural sources including respiration and volcanic activity alongside human emissions.

Methane too arises naturally from wetlands and digestion besides human activity.

Only the synthetic chlorofluorocarbons owe their entire presence to manufacturing.

Chlorofluorocarbons were once widespread in refrigerants and aerosol propellants before the Montreal Protocol.