A number of people are citing the von Storch and Zorita paper as somehow showing that the erroneous MBH98 method did not "matter". I stated previously that the VZ paper indicated that they had inaccurately replicated the hockey stick algorithm – which made their results irrelevant. I have since had some correspondence with von Storch, who I do not regard as being a member of the Hockey Team and who has always been very civil to us in both correspondence and public comments .
von Storch has clarified some points on the methodology in the VZ paper. However, the correspondence has merely confirmed my previous view that they incorrectly replicated the hockeystick methodology of MBH98. I have attached a short script in R here to illustrate the following discussion.
First, we had stated in our Reply that VZ seemed to have done PC calculations on the correlation matrix rather than the decentered data matrix and that this mattered. In our recent correspondence, von Storch stated that they calculated principal components using covariance matrices and did not do SVD on the de-centered data matrix. He then asserted that the results are identical under either methodology, referring me to his text, von Storch and Zwiers.
While one hesitates to directly disagree with von Storch, his text simply does not confirm the point that he requires. Von Storch and Zwiers  (page 301) states that the "SVD of the conjugate transpose of the mxn centered data matrix" [their italics. my bold] extracts the "same information from the sample as a conventional EOF analysis". I agree with this obviously. However, contrary to the claim in his email, this is not the case if the data matrix is uncentered, as you can determine from a simple experiment. The first part of the short script here contains an example showing this. The point can be seen instantly.
Secondly, he suggested that the covariance matrix of a data set is changed by re-centering. I am puzzled by this suggestion, as this is not the case. Again, I have provided an example in the script.
Third, von Storch said that they did get different results under two different methods. Right now, it’s a bit of a guess as to what they did since the stated use of covariance matrices is at odds with the mention of correlation matrices in the article. My guess is that they also did a re-scaling step together with the re-centering step – presumably dividing by the full-period standard deviation in one case and the short-period standard deviation in the other. If so, this would explain the reference to a "correlation matrix" in their article and could also be reconciled with the use of the term covariance matrix in the email. If this surmise as to what they did is correct, the extra hockey stickness in the shortcentered version is only microscopically greater and could be reasonably described as merely a "glitch". There is a correlation of 0.99 between the two different PC1s and only a slight increase of the "hockey stick index" in the NOAMER case. However, this methodology does not replicate the actual MBH98 algorithm and it will not in general lead to the biased creation of hockey stick shaped PC1s as we observed with the MBH98 algorithm.
Fourth, the additional MBH step of using the detrended standard deviation was not used by VZ. This enhances the hockey-stick-ness of the MBH98 PC1, again as shown in the attached script.
Thus, addition to the various problems with the pseudoproxies itemized in our Reply and the VZ failure to deal with bristlecones, I can say confidently that the VZ methodology definitely failed to replicate the hockey stick algorithm and that this failure is material to their findings.