Greenhouse gases

[agnostic]

Greenhouse gases; they puzzle me! What is there about the property of carbon dioxide (which appears as the main villain with a molecular mass of 44) which brings about this effect? As I understand it, it is present in the atmosphere in only a minute quantity - about 0.04% I'm told - yet it is mainly held responsible for causing global warming. On the other hand, water vapour (m.m.18) is said also to be a greenhouse 'gas' yet it is present in vast quantities. The advocates of global warming are not content with these evildoers though, methane (m.m.16) is also held in disfavour. Next they'll be condemning oxygen and nitrogen!! I've given the molecular masses to show that there appears to be no consistency in this regard. Can anyone shed light upon my confusion?