The obligatory link, right off the top: Global Warming: The Cold, Hard Facts?
Ever want to know why some people remain skeptical about global warming? Well, this story is a good indication. Honestly, the whole issue seems less like science, and more like the pre-fight verbal jabs one expects going into a boxing match... based on research and numbers instead of the more colorful "I'll kill you and eat your children!" type of banter, admittedly.
The only real trick here is, part of the fight is actually wrapped up in the preliminaries. Yes, Virginia, there are scientists who believe that, based on the research they've done, man has no notable impact on global warming.
Now, it's easy to try to chalk up the continuing attempts to blame the whole thing on man as "science as religion" as some do... but I think there's an easier explanation. If you were being paid to research something, and you knew the predisposition of the people giving you money, wouldn't that tend to cause you to bias your research in favor of that point of view?