The main difference between H2O and CO2 (apart from the numerical differences of their specific physical properites such as degree of freedom, thermal capacity, physical mass, etc) in terms of their effects on the atmosphere is that water is capable of
condensing into liquid to
form clouds and readily and rapidly moves between surface and atmosphere, daily, seasonally, annually and on even greater time scales, but CO2 does not liquify in the biosphere and transfers over mostly long time periods between surface (primarily oceans, seas, etc) and the atmosphere.