One problem with the General Circulation Models used by the IPCC and NASA/GISS to project unprecedented high temperatures in the future are that all feedback's are considered to be positive. In other words, the relatively small temperature increase that may result from higher atmospheric CO2 concentration levels will cause other changes that will cause further temperature increases. These include higher concentrations of the greenhouse gas water vapor and reduction in the amount of polar ice, so less sunlight is reflected to space. People have pointed out some flaws in this, such as more water vapor in the atmosphere results in more low level clouds that increase reflection to space. Here is a paper that discusses the polar ice issue. It turns out that Antarctic ice is more important than Arctic ice, and the amount of Antarctic ice has been increasing.

http://wattsupwiththat.com/2009/01/10/polar-sea-ice-changes-are-having-a-net-cooling-effect-on-the-climate/