Long term, CO2's worse, but that's probably not the best way to look at it. Excess H2O (water vapor) falls out of the sky as rain, so it's fairly constant (ie.

Long term, CO2's worse, but that's probably not the best way to look at it. Excess H2O (water vapor) falls out of the sky as rain, so it's fairly constant (ie. "maxed out"), and its long term concentration levels are a function of CO2 equivalent gases in the atmosphere. So if you increase CO2 levels, H20 levels will naturally increase as well, and vice versa.