• No one. We neither sought nor received financial support for this project.

• Yes. Our article was read by numerous colleagues in Canada, the US, Australia and Europe, including experts in mathematics and statistics, geology, paleoclimatology, climatology and physics. It was refereed for Environment and Energy by reviewers selected by the editor.

• You would have to ask Nature about the steps taken by their peer reviewers to verify the results in Mann et al. (1998). However, a peer review is not an audit. It is extremely unlikely that the peer reviewers for Nature even requested the original MBH dataset, much less that they carried out the quality control tests that we carried out.

• We have created an audit trail so that third parties can verify these findings for themselves.  This includes what we think is the first Internet posting of the original proxy data used in Mann et al (1998). Some of the points are very easy to verify. To verify the collation errors resulting in duplication of 1980 entries in the data, one needs only inspect a few numbers. We’ve created excerpts from the data and directions to the exact locations in the original data base. Anyone can check this.  Similarly, we’ve created excerpts and pointers in the data base so that anyone can verify the extrapolations and “fills” merely by inspection. To verifying that the MBH data base contains obsolete data, we’ve made graphs to show the differences between the MBH versions and the updated version in every case found (so far); we’ve also included data files showing both versions together and URLs for the updated data. Anyone can check this for themselves. We’ve included computer scripts in R, which will collect the data from the URL site and make the graphs. Verifying the principal components calculations is more work, but we’ve also made the tools available to do this. We’ve provided collated data files for the underlying tree ring series as well as descriptions of how to collect the data. We’ve provided computer scripts showing our principal component calculations and the explained variance using MBH principal components. We’ve also provided a collated version of all the data and scripts for how we replicated the MBH reconstruction. We believe that audit trails are extremely important for this type of analysis and that the Internet provides an ideal mechanism for ensuring public accessibility to such audit trails.

• You’d have to ask them. IPCC have not described what measures of due diligence they carried out. One would surmise that they did not carry out the type of data quality control tests that we did. We understand that Mann was a lead chapter author and, in his IPCC capacity, may not have carried out any due diligence on his own work.

• Our guess is that no one else ever examined the data in detail. MBH never placed the compilation at the World Data Center for Paleoclimatology or at their own FTP sites, as one might have expected. [Nov 4/03: This is not correct. An FTP site was identified in the responses to our paper. It is ftp://holocene.evsc.virginia.edu/pub/MBH98/.] [Nov 11/03 The previous correction was premature. See this update for some further comments on FTP disclosure. Professor Mann has asserted that the data we analyzed was not the data behind MBH98. But it turns out to be identical to what was on the ftp site. So either we did audit the right data or the MBH98 data still haven't been FTP-posted.] When Prof. Mann arranged for the data to be provided in April 2003, it was not immediately available and it’s possible that no one ever requested it before.

• McIntyre has a background in the mineral exploration business. He wanted to see the underlying proxies (before any statistical manipulations by Mann et al.) for exactly the same reason that mining engineers want to look at drill cores in calculating ore reserves. He had seen other proxy data which did not suggest that proxies were behaving differently in the late 20^th century. He had also seen comments by Briffa that tree ring proxies had declined in the second half of the 20^th century and, since MBH data was heavily based on tree rings, wondered how this was reflected in the MBH data. Since he was unable to locate the data in a public archive, he requested it from Prof. Mann.

• In late September 2003, we asked Prof. Mann for additional information on his reconstruction methodology. Prof Mann advised us that he was unable to provide us with such additional information and would be unable to respond to further inquiries, owing to the numerous demands on his time.

• Ultimately, to borrow a phrase, “the proof is in the pudding”. If we’ve identified material errors and defects in this data base, this would prove that we were qualified to do so. As a more detailed answer, both of us have strong backgrounds in handling data and in assessing data quality. McIntyre’s intuition that the data should be examined like drill core shows that the practical experience and scepticism that one acquires in the mineral exploration industry was not misplaced here. Moreover, the paper is about statistical and “accounting” issues, both of which are well within our ranges of experience and competence. While McIntyre’s background is more on the practical side and McKitrick’s more on the academic side, both have strong mathematical skills and statistical training.

• McKitrick is a Senior Fellow of the Fraser Institute, a Canadian policy think tank that has taken a stand against Kyoto. McIntyre has worked many years in the mineral exploration industry. McIntyre is a shareholder of a micro-capital energy exploration company, CGX Energy, has acted in the past as a consultant to CGX and sub-leases office space from CGX. CGX is not a producing company and, as a company, has no views on Kyoto and has provided no financial support to this study.

• No. We’re saying that Mann et al., based on their methodology and corrected data, cannot claim that the 20^th century is warmer than the 15^th century – the nuance is a little different. To make a positive claim that the 15^th century was warmer than the late 20^th century would require an endorsement of both the methodology and the common interpretation of the results which we are neither qualified nor inclined to offer.

What led you to publish in E&E rather than Nature?

• After receiving the MBH98 data from Scott Rutherford and Michael Mann, McIntyre posted a series of observations about curiosa in the data on the internet discussion group climateskeptics. Sonja Boehmer-Christiansen invited McIntyre to consider writing up his work for submission and McIntyre agreed. Subsequent to this, McKitrick joined with McIntyre in the analysis and preparation of an article. McKitrick suggested that an article be submitted to Nature and a 1500-word version (to fit the word limit in Nature) was drafted. But after showing it to some scientific colleagues who were not familiar with the issue, we were advised that it was too short a format to convey the scope of the argument. So we chose to write a longer paper first in order to get the full body of material out. It has been suggested to us that we write a letter to Nature summarizing what is spelled out in the longer paper and we are considering this.

What if someone comes along and finds errors in your work?

• We've made it as easy as possible for them to do so. We’ve displayed all our data and all our methods. We welcome the scrutiny.

How closely did you replicate the original MBH98 results using the data they supplied you?

• As we state in the paper we achieved substantial success in replication, but some differences remained between their results and ours. We were unable to obtain advice from them on either data questions or methdology questions, so we carried on with the rest of our analysis. Figure 6 in our paper shows the comparison of their temperature PC1 and ours. The comparison of the final NH index versions looks very similar to that between the PC1 versions:
  
  In their reply (see above) MB&H can also obtain a large variation in the 15th century, similar to ours, by making some changes that approximate some of the changes between our versions.

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