In reference to the last Fstop post:
The Earth is essentially a system that will respond to certain factors. So if cloud cover increases, will temperatures drop from reflection, or will they increase due to absorbtion? I am not a climatologist, and I cannot give you the answer to that one. But as certain factors change, they force others to move along with them. So if you cool the planet, and snow fall increases in area, then albedo will increase, and the sun's energy will be more readily reflected. In the same sense, if you heat the planet, there will be less snow cover, more vegetation and more absorbtion of sun energy. As the planet continues to warm however, and certain areas perhaps dry out and lose vegetation or become desert, the albedo will increase again... It should be evident by now that climate studies are:
1. Highly hypothetical
2. Depend on innumerous factors
3. Are highly prone to long term inaccuracy due to #2.
Albedo:
http://en.wikipedia.org/wiki/Albedo
I know that in the history of the planet, there were events which possibly led to the
entire planet becoming a giant snowball
http://en.wikipedia.org/wiki/Snowball_earth.
However, an event like this is considered impossible today due to the alignment of the continents relative to the equator.