Ross McKitrick 

 Comment by McIntyre and McKitrick on Corrigendum, July 1, 2004

July 1, 2004 Corrigendum by Mann, Bradley and Hughes

Internet response by MBH (Nov. 2003)

Supplementary Information to McIntyre and McKitrick (2003) 

McIntyre and McKitrick (2003) 


Comments on MM03 




The purpose of this webpage is to provide supplementary information and comments to ongoing research on the use of proxy information to develop temperature reconstructions. 


The principal focus to date has been on analyzing the reconstruction by Mann et al. in Mann, Bradley and Hughes (1998) and 1999, because this reconstruction was used by the International Panel on Climate Change, especially in its Third Assessment Report (2001) to support claims that the 1990s were the warmest decade and 1998 the warmest year of the millennium, and was applied in the main promotional graphics used by IPCC, as shown below. However, we are in the process of examining the other major multi-proxy studies (Jones et al. (1998), Crowley and Lowery (2000), Briffa et al. (2001), Esper et al. (2002), Mann and Jones (2003)).   


FIGURE 1. NH Temperature Reconstruction - IPCC Version of MBH98, MBH99


Despite the extensive policy reliance on this presentation, IPCC did not itself audit or verify the data and methods of MBH98 and MBH99. To our knowledge, other than our efforts, no other person or institution has attempted any replication or verification. (See here for some comments on replication standards.)   


When we attempted to replicate the results of MBH98, we encountered many data errors and defects in the underlying data set to which we had been directed, which we reported on in McIntyre and McKitrick (October 2003). These errors and defects appeared to include collation errors, use of obsolete data, incorrect principal components calculations for tree ring networks, unjustified truncation or data, geographical mislocations etc. We re-collated tree ring data from original sources and obtained updated versions wherever possible. (See SI.) When we carried out our own re-construction, we obtained quite different results - with high early 15th century values, which prevented the MBH98 claim of 20th century uniqueness, as shown in the diagram below:


FIGURE 2. NH Temperature Reconstructions from MM03.


MM03 occasioned considerable controversy. First, Mann et al. argued that they had sent us the wrong data and this compromised the MM03 calculations. Mann then deleted the "wrong" data from his FTP site. Since we re-collated the compromised data, this criticism had no bearing on our own calculations, although it did have a bearing on a couple of our criticisms of MBH98. The matter is discussed here, but has little bearing on the scientific outcome of the dispute. Professor Mann did however provide a different FTP location said to be the location of MBH98 proxy data. Since November 2003, we have examined this FTP location and found many additional data errors and defects, additional to those described in MM03. Some of these issues have been addressed in the recent Nature Corrigendum; there are many data errors in MBH98 which remain unacknowledged. 


Second, Mann et al. argued that the differing results could be attributed to different handling of tree ring principal component calculations - in particular, that MM03 had not carried out a "stepwise" calculation - and to our use of a different version of the TTHH tree ring series. They produced the following emulation of our results by changing 3 indicators. They asserted that the use of a "stepwise" procedure for tree ring principal components resulted in the use of 159 series, rather than the 112 series referred to in MBH98 and listed in pcproxy.txt. 


FIGURE 3. NH Reconstructions from Mann et al. (2003)


Since the principal components calculations in MBH98 were described as "conventional" and there was no mention of 159 series, we carried out a conventional principal components calculation using the maximum period in which all sites were available. As it turned out, this procedure resulted in the NOAMER PC1 and STAHLE/SWM PC1 being unavailable in the AD1400 step. We used a version of the TTHH series which began later (and ended later), because this was the later version archived by Jacoby (which was calculated well before the publication of MBH98). We make no apology for not using obsolete data; however, since the TTHH series doesn't start until 1459 in the MBH98 version, it is irrelevant anyway.  As it turns out, the presence or absence of the Stahle/SWM PC1 has virtually no effect on early 15th century values.


The differences between results depend entirely on the calculation of the NOAMER PC1. We have closely examined this matter and have identified an error in the MBH98 procedure for calculating principal components, which we have submitted to a journal. This one error accounts for most of the difference between our results. We have also been able to identify one other data misrepresentation, which accounts for the balance of the difference between our results. We anticipate that these results will soon become public. 


We have also endeavoured to ensure a complete public record with respect both to MBH98 and other multi-proxy studies. It seems scandalous to us that there should be anything other than copious public disclosure of all data, methods and source code in papers relied upon for major public policy. We have had some partial success in this endeavour with the new SI for MBH98, which provides considerable new information on this study. Nonetheless, the public record remains incomplete and multi-proxy authors have refused to provide key information. The public disclosure record for the studies which supposedly confirm MBH98 (e.g. Crowley and Lowery (2000), Briffa et al (2001) etc.) is actually worse than MBH98. We have endeavoured here to provide a complete record of all data and methods used in MM03, including all scripts. (See SI to MM03) 


As noted above, our studies have progressed significantly since MM03 and we hope to be able to comment more fully our submission in review in the near future. 


To contact us: Email: Stephen McIntyre