Al Gore's Earth in the Balance 4: Clouds

A few posts ago, in writing about Al Gore's Earth in the Balance: Ecology and the Human Spirit, I mentioned Al Gore's reference to an argument that the greenhouse effect could actually lead to cooling, since it would result in more clouds.  Gore also referred to climate-change skeptic Richard Lindzen, who teaches at MIT.  In my latest reading, on page 90, Gore interacts more with the clouds argument:

"...speculation that the cloud system might somehow cancel the effects of all the extra greenhouse gases has not withstood analysis.  It is true that the water vapor in clouds both contributes to the greenhouse effect by absorbing radiant energy and plays a cooling role by scattering light, in part back to space; as a result, any change in the number and distribution of clouds would have a big impact.  But the evidence to date strongly points to the conclusion that water vapor seems, unfortunately, to amplify the warming trend as it traps even more infrared heat that might otherwise escape from the atmosphere.  Though there is more uncertainty where clouds themselves are concerned, most water vapor is outside clouds, and clouds too may magnify the warming rather than lessen it.  Indeed, the leading proponent of the idea that water vapor serves as a cooling thermostat, Richard Lindzen, publicly withdrew his hypothesis on how that might happen in 1991."

I found this interesting because Gore argues that, while clouds have a cooling effect, they can also have a warming effect.  I guess that the question is which is greater, the warming or the cooling effect.