This is significant: Read what Michael Mann, the guy who produced the graph that allegedly "really clinches the idea of man-made global warming" says about his own work

Case closed: “Climategate” was manufactured | Bad Astronomy | Discover Magazine

A lot of these attacks can be traced back to the famous "hockey stick" diagram, showing how Earth’s temperatures have been increasing rapidly in recent times. This graph is what really clinches the idea of man-made global warming, and so has been the epicenter of the manufactroversy. The fact that Dr. Mann has been cleared again, and that his data are good, shows that this graph is even more solid — or at least is not as weak as so many would lead you to believe.

1999: Significant Michael Mann email

[Mann] And I should point out that Chris, through no fault of his own, but probably through ME not conveying my thoughts very clearly to the others, definitely overstates any singular confidence I have in my own (Mann et al) series.