It's hard for deserts to lose much heat at the ground because the evaporation term in the surface energy budget is small compared to the moist tropics. This has little to do with water vapor feedback. If you could make the Sahara moister, the surface would cool even if you increase CO2 a bit.
It also doesn't follow at all from Clausius-Clapeyron that global cloudiness (or low clouds in particular which control the albedo more than any other kind) will increase in a warmer world. I don't understand andre's objections at all to sylas...they're repetitive and rather ill-posed.