Dear Karl,

In November 2003, we wrote a complaint to you regarding our inability to obtain information from Professor Mann on sources and methods in connection with Mann et al. (1998).  As a result of Nature’s consideration, it is our understanding that Mann et al. have been required to issue a Corrigendum on certain matters raised in our complaint and to provide a new Supplementary Information. We were shown the page proofs for Professor Mann's Corrigendum in early March and provided comments to Nature on the Corrigendum. To our knowledge, the Corrigendum has not been published and we are interested in its status.

In the meantime, Professor Mann has put up a new FTP site for MBH98 ftp://holocene.evsc.virginia.edu/pub/sdr/temp/nature/MANNETAL98 , which I presume is the one prepared in response to the request from Nature. Professor Mann has referred to this FTP site in a submission to Climatic Change criticizing McIntyre and McKitrick (2003), on which I was asked by Climatic Change to act as a reviewer. I have examined the new FTP site in detail and I want to bring to your attention the following items:

First, Mann et al. (1998) described 11 “experiments”, which were individual stepwise calculations. RE statistics on these “experiments” were reported in the original Nature SI. We requested data on the results of these experiments originally from Professor Mann, referring particularly to the residuals; and referred to his refusal in our original complaint to Nature over 6 months ago. We again requested this information in connection with reviewing the submission to Climatic Change and again it was refused. Professor Mann said that he had neither the “time nor the inclination” to provide the results of his “experiments”. The results of his "experiments" establishing the fit of his statistical model are not available on the new SI. This continued refusal to provide the results of his “experiments” is unsatisfactory and I request that you persuade Professor Mann to provide them. This would necessarily include the temperature principal components, the temperature reconstruction and the residuals. This is not an onerous request. From my own experience in dealing with these models, it would take only a few minutes and it takes more time to argue about it than to do it. But even if it took some time, there are no good grounds for refusing this information and the continued refusal should be of concern.  

At the time of my prior comments on the proposed Corrigendum, I did not have access to the proposed new SI. There are other issues in connection with the new FTP site, which you may wish to consider in connection with finalization of the planned Corrigendum.

Professor Mann has recently stated that 159 series are required for his calculations – a figure which was not given in Mann et al (1998). A reader could not identify the 159 proxy series at Professor Mann’s FTP site or the series used in each step of the calculations. The new FTP site allows the user to identify the series used in each step, but they do not add up to 159 series.

Mann et al. (1998) provided incorrect locations for a number of instrumental series as well as an incorrect reference to Bradley and Jones (1992) for these series. The attribution is now stated as  "NOAA Climate Center" which is a very inadequate citation, given the thousands of series at NOAA. The incorrect locations have not been corrected in the new SI or acknowledged in the proposed Corrigendum.

While there is some additional information on the data and computational routines at the new SI, the information continues to be insufficient to permit a reader to independently reconstruct their results.

The new FTP site contains a revised description of the principal component calculation methods of Mann et al. (1998), as follows:

All predictors (proxy and long instrumental and historical/instrumental records) and predictand (20th century instrumental record) were standardized, prior to the analysis, through removal of the calibration period (1902-1980) mean and normalization by the calibration period standard deviation. Standard deviations were calculated from the linearly detrended gridpoint series, to avoid leverage by non-stationary 20th century trends. The results are not sensitive to this step (Mann et al, in review).

This statement is materially different from the description in Mann et al. (1998), but there is no reference to this correction in the Corrigendum proof which we were shown.

Further, the last sentence in the above quotation is a direct reference to Professor Mann’s reply to our pending submission to Nature concerning principal components methodology in Mann et al. (1998). While we obviously disagree with the claim in this sentence, we are particularly concerned with Professor Mann’s premature discussion of this issue, which is an apparent contravention of the following Nature confidentiality policy:

The responders (defined as the authors of the published contribution that is the subject of the comment, and no-one else) must keep the comment confidential and must not use it for their own research or for any other purpose apart from replying to the comment, nor can they distribute it without first obtaining Nature's permission.

In addition to the posting at his FTP site, Professor Mann has used this FTP site as support for a submission to Climatic Change criticizing us, and, in turn, he has cited the submission to Climatic Change as support for criticisms of us made in the course of a major article in Reviews of Geophysics published in May 2004.