As the Wegman Report says:
While the work of Michael Mann and colleagues presents what appears to be compelling evidence of global temperature change, the criticisms of McIntyre and McKitrick, as well as those of other authors mentioned are indeed valid.
"Where we have commonality, I believe our report and the [NAS] panel essentially agree. We believe that our discussion together with the discussion from the NRC report should take the 'centering' issue off the table. [Mann's] decentred methodology is simply incorrect mathematics …. I am baffled by the claim that the incorrect method doesn't matter because the answer is correct anyway.
Method Wrong + Answer Correct = Bad Science.
The papers of Mann et al. in themselves are written in a confusing manner, making it difficult for the reader to discern the actual methodology and what uncertainty is actually associated with these reconstructions.
It is not clear that Dr. Mann and his associates even realized that their methodology was faulty at the time of writing the [Mann] paper.
We found MBH98 and MBH99 to be somewhat obscure and incomplete and the criticisms of MM03/05a/05b to be valid and compelling.
Overall, our committee believes that Mann's assessments that the decade of the 1990s was the hottest decade of the millennium and that 1998 was the hottest year of the millennium cannot be supported by his analysis.
[The] fact that their paper fit some policy agendas has greatly enhanced their paper's visibility… The 'hockey stick' reconstruction of temperature graphic dramatically illustrated the global warming issue and was adopted by the IPCC and many governments as the poster graphic. The graphics' prominence together with the fact that it is based on incorrect use of [principal components analysis] puts Dr. Mann and his co-authors in a difficult face-saving position.
As Phelim McAleer & Ann McElhinney say:
Once again, the facts have refuted global warming hysteria. Radical environmentalists who love to hate fossil fuels have stretched the truth so many times that it's a wonder anyone believes them.
H/T: Not Evil Just Wrong