It's more complicated than he makes it seem:
On [ame="http://en.wikipedia.org/wiki/February_12"]February 12[/ame], [ame="http://en.wikipedia.org/wiki/2005"]2005[/ame], Stephen McIntyre and Ross McKitrick published a paper in
[ame="http://en.wikipedia.org/wiki/Geophysical_Research_Letters"]Geophysical Research Letters[/ame] that claimed various errors in the methodology of Mann
et al. (1998). The paper claimed that the "Hockey Stick" shape was the result of an invalid [ame="http://en.wikipedia.org/wiki/Principal_component_analysis"]principal component[/ame] method.
[16] They claimed that using the same steps as Mann
et al., they were able to obtain a hockey stick shape as the first principal component in 99 percent of cases even if trendless [ame="http://en.wikipedia.org/wiki/Red_noise"]red noise[/ame] was used as input.
[17] This paper was nominated as a journal highlight by the [ame="http://en.wikipedia.org/wiki/American_Geophysical_Union"]American Geophysical Union[/ame],
[18] which publishes GRL, and attracted international attention for its claims to expose flaws in the reconstructions of past climate.
[19] The IPCC AR4 says this paper
may have some theoretical foundation, but Wahl and Amman (2006) also show that the impact on the amplitude of the final reconstruction is very small.
[5]
And in the end the Hockey Stick graph was vindicated:
Congress was especially concerned about Mann’s reported refusal to provide data. In June 2005, Congress asked Mann to testify before a special subcommittee. The chairman of the committee ([ame="http://en.wikipedia.org/wiki/Joe_Barton"]Joe Barton[/ame], a prominent global warming skeptic) wrote a letter to Mann requesting he provide his data, including his source code, archives of all data for all of Mann's scientific publications, identities of his present and past scientific collaborators, and details of all funding for any of Mann's ongoing or prior research, including all of the supporting forms and agreements.
[22] The [ame="http://en.wikipedia.org/wiki/American_Association_for_the_Advancement_of_Science"]American Association for the Advancement of Science[/ame] viewed this as "a search for some basis on which to discredit these particular scientists and findings, rather than a search for understanding."
[24] When Mann complied, all of the data was available for McIntyre. Congress also requested that third party science panels review the criticisms by McIntyre and McKitrick. The Wegman Panel
[25] and the National Academy of Sciences
[26] both published reports. McIntyre and McKitrick (2005) claim that 7 of their 10 findings in 2003 have been largely confirmed by these reviews.
[27] Nature reported it as "
Academy affirms hockey-stick graph - But it criticizes the way the controversial climate result was used."
[28]