What exactly is your theory on water vapor here?
It's transient. You have evaporation -- which increases in warmer temperatures -- which leads to water vapor, which leads to clouds, which function as a greenhouse gas and trap heat.
But clouds release their moisture (precip) or evaporate quickly -- like, in a matter of days. Gases like methane and Co2 do not -- they can stick around decades.
If clouds didn't we would've had a run away greenhouse effect long ago and we'd be boiling right now.
The key is warming the atmosphere (from some other non cloud source) That allows the atmosphere to hold more water vapor, ultimately. (which contributes to warming from water vapor)
The models probably struggle with clouds because they're a very short lived, transient item.
I really don't care about the IPCC report. Nobody is interested in taking drastic steps to reduce Co2 anyway.
I deal with confidence levels -- there is lots of evidence to support a significant man-made contribution to global warming.