I have always had serious doubts about the ability of the UN IPCC to accurately model climate with current computer technology. I have experience with large thermal models and know that accurate modeling is difficult, and becaomes virtually impossible for a non-linear, dynamically unstable system. This caused me to have no confidence in the temperature projections the IPCC makes. I don't know to what extent man is affecting Earth's temperature, and I don't think the IPCC does either. Here is an article that descibes some of the defiencies of the IPCC's models. One item that all doubters cite is that cloud cover is very important, and so assuming the amount of cloud cover, as is done in the IPCC models, is tantamount to assuming the average temperature.