What is a 'moist greenhouse effect'? What is a moist greenhouse effect? I've heard that this is where all the water on a planet is quickly driven into space. However,  I cannot find much information on this- is it a relatively new (or obsolete) idea and what causes it? Also, any links regarding this would be appreciated. 
 A: 
What is a 'moist greenhouse effect'? 

That's the Earth's fate in a billion years or so.
Right now, and for millions of years to come, the very sharp temperature inversion and the very cold temperatures at the tropopause keep the stratosphere very, very dry. This won't always be the case. The problem is that yellow dwarf stars such as our Sun output ever more energy as they age. The Sun will be shining about 10% brighter in a billion years than it does today. That extra energy from increased sunlight may be enough to push significant amounts of water vapor into the stratosphere and beyond.
That upper atmospheric water vapor will be subject to the more energetic portion of the solar spectrum, which has enough energy to dissociate water. The resultant hydrogen can leave the atmosphere. Our atmosphere currently loses about three kilograms of hydrogen per second to outer space. That loss rate will grow much larger a billion years from now, and the oceans will gradually disappear.
A: From the book "Terraforming: The Creating of Habitable Worlds":

This seems pretty unambiguous. Water is a greenhouse gas. When the atmosphere gets warm, more water evaporates -> more greenhouse gas, more heating. Boom, no more life on earth.
