The atmosphere water content is self-regulating, since it works as a cycle (water evaporating, condensing and raining down, with the atmospheric content mainly

The atmosphere water content is self-regulating, since it works as a cycle (water evaporating, condensing and raining down, with the atmospheric content mainly regulated by how much vapor the air can hold). Not so with CO2. There is no similar "excess" threshold for CO2 after which it would "rain down".