In 2007, the hockey stick originally produced by Mann et al, was verified by the NAtional Academy of Sciences.

More importantly, there is a certain fixated myopia on the part of the denier crowd. There are many other groups that have studied vast amounts of proxy data to reconstruct global temperatures from the distant past.

There is not one hockey stick graph produced by one team.

There is actually a hockey team.

This video actually gives the history quite nicely, and debunks the medieval warming period crap on the way.

Youtube Video