The problem with Mann’s hockey stick is that he used proxies (tree rings via dendranology) to create a relatively smoothed, long term climactic history and then grafted on contemporary temperature records which produced the inflection point.

What Mann has failed to do is go back and continue the climate record into modern times using the same data source (the tree rings) to show the same inflection point.

Mann is a true believer and, if you follow his own comment streams that he posts on blogs that argue with him, he lacks any sense of uncertainty in the firmness of his conclusions and is quick to make threats of legal action for defamation against on-line critics.

That doesn’t prove or disprove anything but it should get people to be more skeptical of his work. There are records (both written and geological) that contradict the relative constancy of the past that Mann’s proxies describe. The little ice age poses a problem, but is often dismissed as a local European event which blunts its impact on a global record.

Here is an article that discusses some weaknesses in Mann’s proxies that is fairly level headed. newscientist.com

As I have learned, attacking Mann has no impact on the debate anymore anyway. I am told that even Al Gore has pulled Mann’s hockey stick from his presentations.

Mann provided political shock value that gave juice to the catastrophists. As a luke warmer myself the hyperbolic catastrophists are about as helpful to understanding what is going on as are those who claim that changing the chemical composition of the atmosphere has no impact on how it behaves.