The Global Circulation Models (GCMs) do not accurately model clouds, as was mentioned in the Hadley CRU emails. All of the GCMs used by the UN IPCC as proof of the apocalyptic AGW hypothesis have clouds as a positive feedback. That is, as the earth warms due to increased atmospheric CO2 concentration, clouds cause the increase to be amplified. Satellite data indicates that the opposite is true, that clouds decrease the warming. Here is a discussion by climatologist Dr. Roy Spencer.