Global-warming potential - Wikipedia, the free encyclopedia
Water Vapor Feedback and Global Warming, Held & Soden, Annual Review Energy Environment (2000)
In fact, it’s so well-known that most times in papers it isn’t repeated. No one involved in atmospheric physics is confused about the subject.
Why the focus on CO2 in that case?
Water vapor arguably lies at the heart of all key terrestrial atmospheric processes. Humidity is essential for the development of disturbed weather, influences (directly and indirectly through cloud formation) the planetary radiative balance, and influences surface fluxes and soil moisture. Water vapor is the only radiatively important atmospheric constituent that is sufficiently short‐lived and abundant in the atmosphere so as to be essentially under purely natural control..
Tropospheric Water Vapor, Convection & Climate, Sherwood, Roca, Weckwerth & Andronova, Review of Geophysics (2010)
Emphasis added.
The point is that water vapor responds to climate – and therefore influences climate as a feedback. The concern is that humans adding CO2 to the atmosphere will cause a change to the climate and water vapor will have a feedback effect (see, for example, Clouds and Water Vapor – Part One and subsequent articles).
It is quite difficult for humans to add water vapor to the atmosphere. The oceans are a vast source of water, and just above the surface of the ocean the atmosphere is saturated
Water Vapor vs CO2 as a ?Greenhouse? Gas | The Science of Doom
So add more co2 into the atmosphere=more evaporation=more warming. lol But without co2 the water would freeze out of the atmosphere within a short period geologically speaking.