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.