"New calculations show that doubling of carbon dioxide (CO2) will increase average global temperature by only about 1F (degrees Fahrenheit) or 0.55C (degrees Centigrade), much less that the range of 2C to 4.5C estimated by the United Nations International Panel on Climate Change (IPCC)."

http://junkscience.com/jan08/Global_Warming_Not_From_CO2_20080124.pdf