Myth vs. Fact Regarding the "Hockey Stick"

The second falsehood holds that there are errors in the Mann et al (1998, 1999) analyses, and that these putative errors compromise the “hockey stick” shape of hemispheric surface temperature reconstructions. Such claims seem to be based in part on the misunderstanding or misrepresentation by some individuals of a corrigendum that was published by Mann and colleagues in Nature. This corrigendum simply corrected the descriptions of supplementary information that accompanied the Mann et al article detailing precisely what data were used. As clearly stated in the corrigendum, these corrections have no influence at all on the actual analysis or any of the results shown in Mann et al (1998). Claims that the corrigendum reflects any errors at all in the Mann et al (1998) reconstruction are entirely false.

False claims of the existence of errors in the Mann et al (1998) reconstruction can also be traced to spurious allegations made by two individuals, McIntyre and McKitrick (McIntyre works in the mining industry, while McKitrick is an economist). The false claims were first made in an article (McIntyre and McKitrick, 2003) published in a non-scientific (social science) journal “Energy and Environment” and later, in a separate “Communications Arising” comment that was rejected by Nature based on negative appraisals by reviewers and editor [as a side note, we find it peculiar that the authors have argued elsewhere that their submission was rejected due to 'lack of space'. Nature makes their policy on such submissions quite clear: "The Brief Communications editor will decide how to proceed on the basis of whether the central conclusion of the earlier paper is brought into question; of the length of time since the original publication; and of whether a comment or exchange of views is likely to seem of interest to nonspecialist readers. Because Nature receives so many comments, those that do not meet these criteria are referred to the specialist literature." Since Nature chose to send the comment out for review in the first place, the "time since the original publication" was clearly not deemed a problematic factor. One is logically left to conclude that the grounds for rejection were the deficiencies in the authors' arguments explicitly noted by the reviewers]. The rejected criticism has nonetheless been posted on the internet by the authors, and promoted in certain other non-peer-reviewed venues (see this nice discussion by science journalist David Appell of a scurrilous parroting of their claims by Richard Muller in an on-line opinion piece).

The claims of McIntyre and McKitrick, which hold that the “Hockey-Stick” shape of the MBH98 reconstruction is an artifact of the use of series with infilled data and the convention by which certain networks of proxy data were represented in a Principal Components Analysis (“PCA”), are readily seen to be false , as detailed in a response by Mann and colleagues to their rejected Nature criticism demonstrating that (1) the Mann et al (1998) reconstruction is robust with respect to the elimination of any data that were infilled in the original analysis, (2) the main features of the Mann et al (1998) reconstruction are entirely insensitive to whether or not proxy data networks are represented by PCA, (3) the putative ‘correction’ by McIntyre and McKitrick, which argues for anomalous 15th century warmth (in contradiction to all other known reconstructions), is an artifact of the censoring by the authors of key proxy data in the original Mann et al (1998) dataset, and finally, (4) Unlike the original Mann et al (1998) reconstruction, the so-called ‘correction’ by McIntyre and McKitrick fails statistical verification exercises, rendering it statistically meaningless and unworthy of discussion in the legitimate scientific literature.

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