Global climate modeling is far from an exact science, but to the politicos it appears to be gospel.
Here is an article by Arthur B. Robinson, Sallie L. Baliunas, Willie Soon, and Zachary W. Robinson, of the Oregon Institute of Science and Medicine, entitled "Environmental Effects of Increased Atmospheric Carbon Dioxide". It includes a petition purpotedly signed by 19,000 scientists.
It is a fairly long look at the data on Earth tempature data, carbon dioxide in the atmosphere, and climate impact. It is not very good news for the "Global Warming is Real and the Earth is going to end" crowd. Here are some excerpts:
"Not one of the temperature graphs shown in figures 4 to 7, which include the most accurate and reliable surface and atmospheric temperature measurements available, both global and regional, shows any warming whatever that can be attributed to increases in green-house gases."
"There are no experimental data to support the hypothesis that increases in carbon dioxide and other greenhouse gases are causing or can be expected to cause catastrophic changes in global temperatures or weather. To the contrary, during the 20 years with the highest carbon dioxide levels, atmospheric temperatures have decreased."
There are a lot of people who believe global warming is real. Of course, there are a lot of people who believe in the Easter Bunny, too. Global climate modeling involves a complex combination of sciences in aerodynamics, physics, chemistry, and computational mathematics.
The statistical modeling by the leading authors on the existence of global warming was analyzed by a group of Statisticians, including my advisor at George Mason University, Dr. Ed Wegman, and resulted in their congressional testimony, an excerpt of that you can find here.
Here is an excerpt from Congressman Ed Whitfield's (Kentucky) opening statement from the hearings on "Questions Surrounding the 'Hockey Stick' Temperature Studies: Implications for Climate Change Assessments", on July 27, 2006:
"Dr. Wegman was not seeking to impugn the integrity of any of the scientists who work in this area, but it is clear that peer review somehow failed to pick up the flaws in the hockey stick studies. Dr. Wegman simply raises the possibility that, given the evident publishing relationship among the authors of many of the relevant works, combined with the failure to involve statisticians, Dr. Mann's peers may have been too close to the topic to scrutinize the studies as rigorously as they might have. Whatever the case, Dr. Mann's peers failed to catch the errors Wegman, the NRC, and McIntyre identified."