I'm interested in issues related to Global warming and therefore started to read about it from this website -->> link
As I was reading I got stuck in the third paragraph of
What are Greenhouse gas ? section. It says
Secondly, CO2 tends to remain in the atmosphere for a very long time (time scales in the hundreds of years). Water vapor, on the other hand, can easily condense or evaporate, depending on local conditions. Water vapor levels therefore tend to adjust quickly to the prevailing conditions, such that the energy flows from the Sun and re-radiation from the Earth achieve a balance. CO2 tends to remain fairly constant and therefore behave as a controlling factor, rather than a reacting factor. More CO2 means that the balance occurs at higher temperatures and water vapor levels.
I do not understand the whole paragraph and also specially the controlling and reacting factor. Please help .Thankyou in advance.