H2O is 300-400 times more potent as a greenhouse gas (roughly the same quality and 300-400 times more prevalent). Its use in the heat cycle of the earth is clear, and unambigous. It is difficult to model however, and in order to accurately model climate change, bigger factors have to be modelled accurately first. If CO2 effect is less than the noise of H2O, then how do you know it is CO2?
DK
The warmist argument is that C02 will warm things slightly, causing greater H20 evaporation from the oceans which will cause much greater warming. My argument back has been that any ocean evaporation should then cause more warming than C02 which should then cause even more evaporation in a runaway warming event. But, that has not happened and the oceans have been there for over 100 years.