Climate Change: CC Models / The IPCC
Climate models are wrong—as is every model ever made, anywhere, about anything. No model is perfect. But climate models are valuable for helping us figure out what we don't know and what we need to know. They do a nice job of "postdicting" recent climate changes, making it worth considering their projections for future changes. Climate models figure prominently in IPCC documents, but are not the only basis of the IPCC findings and recommendations.
Analysis of Climate Policy Targets under Uncertainty (Report 180 from MIT's Joint Program on the Science and Policy of Global Change, Webster et al. 2009): Long, technical, but very accessible statistical analysis of the probabilities of various climate changes given different levels of global mitigation. Strongly recommended. (click on last line to download PDF)
FAQ on Climate Models: RealClimate, 2008.
The Physics of Climate Modeling (Gavin Schmidt): 2007 NASA Fact Sheet
The Intergovernmental Panel on Climate Change: This site is the portal to thousands of pages of peer-reviewed reports written by a huge international cast of scientists. The three main Working Groups were Scientific Basis; Impacts, Adaptation, and Vulnerability; and Mitigation of Climate Change.