Here is a great article and profile of Steve McIntyre, the man who single handedly debunked Michael Mann's "Hockey Stick" theory seen in Al Gore's horrible film. An excerpt:
The hockey stick, featured in the 2001 report by the UN’s Intergovernmental Panel on Climate Change, had a profound influence on policy worldwide, and played a starring role in presentations like Al Gore’s An Inconvenient Truth. The McIntyre-McKitrick critique called attention to uncertainties in its temperature reconstructions dating back before 1600, to certain problems with dendrochronology (the use of tree rings to estimate past temperatures), and to issues with the statistical calculations underlying the hockey stick. Some climatologists insist that the graph tells the same story when you correct for all this, but much of the critique is now accepted, and the hockey stick, whose weaknesses are better understood, has itself become a somewhat inconvenient distraction for climatologists and environmentalists.