[pdonis]

> increased evaporation - water vapor is a potent green house gas

But its lifetime in the atmosphere is very short; the evaporated water vapor condenses in the upper atmosphere into clouds and precipitation.

What longer term numbers I have seen indicate that the average water vapor content of the atmosphere has been roughly constant during the warming of the last half century or so.

[labster]

More importantly there is tons and tons of water in the atmosphere, even in so-called dry places. There’s just no wiggle room in the water vapor spectral bands, optical path is pretty constant.

We will probably get more water vapor in the future but most of the PWAT ends up in clouds. And that’s where the feedbacks get interesting, cloud height is very important to radiative balance and there are a couple of indirect effects to consider too.