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Aug 10, 2004 McIntyre to Ziemelis

 

Dear Karl,

 

We are disappointed that Nature has decided not to publish our submitted Communication, especially as the principal grounds appear to be the small word allotment in the Communications Arising section. We respectfully disagree with the conjecture that our work would be of interest to only a few specialists. The original Mann et al. paper has been widely applied and our previous commentary attracted considerable public interest. Be that as it may, the referees expressly encouraged us to continue our analysis of MBH98 and of multiproxy calculations generally and one of them expressly stated that our efforts should not be “hampered”.

 

In this spirit we are writing to reiterate long-standing requests for data and results from MBH98, which we have already communicated on several occasions. You had stated that these requests would be resolved in the new SI, but unfortunately this is not the case. While you are undoubtedly weary of this correspondence, our original request for disclosure was reasonable and remains reasonable. It is only the unresponsiveness of the original authors that is placing a burden on you and your associates. Some of these items have been outstanding for 7 months. They were not attended to in the new SI and need to be dealt with promptly.

 

In particular, we still seek:

 

  1. the results of the 11 “experiments” referred to in MBH98, including:

(a)   the temperature principal components (69 series for all 11 steps);

(b)   the NH temperature reconstruction (11 series from the start of each calculation step to 1980);

(c)   the residuals (11 series from the start of each calculation step to 1980).

  1. a list of the 159 series said to have been used in MBH98.
  2. source code.

Since their claims of skill in reconstructing past climates depend on these “experiments” and their estimation of confidence intervals is based on the residual series, it is unnecessary to explain why these data are of interest. Again, we have repeatedly requested this data.

 

The new SI contains listings of the series used in the stepwise reconstruction.  We collated the available series and were only able to identify 139 distinct series and we are concerned at the discrepancy. Since considerable emphasis has been placed by Mann et al. on the need to use 159 series, we re-iterate our request to see the actual list of these series – again a longstanding request.

 

The code is evidently at hand since it was used to generate the Supplementary Information for Mann’s recent response to our submission to Nature. It is surprising that, instead of simply providing this code, the new SI only provides a verbal description of it (AlgorithmDescription.txt) which still does not suffice to permit exact replication. We do not understand why Nature has acquiesced in this.

 

In light of these continuing disclosure problems, as well as points raised in the exchange over our Communication, we are obliged to ask the following questions, which are either not clarified in the new SI or result from the new SI itself:

 

  1. Mann et al. stated (in several places) that they carried out fresh calculations of principal component series for each region and each calculation interval. But the SI shows principal component series are not freshly calculated in every region and every calculation interval. What, then, is the criterion for deciding when to carry out a fresh calculation of the PC series in a region and calculation interval? Also, the present description of this process in the new SI is inaccurate and needs to be corrected.
  2. In the Corrigendum, Mann et al. purport to explain the discrepancy between the listing of series in the original SI and the series actually used by reference to criteria stated in Mann et al (2000), which states that “clear a priori” criteria were used for proxy selection. But while the quality control rules ostensibly used for screening selected proxies are stated in the reference, the a priori criteria themselves were not stated in the reference or the new SI. What are the “clear a priori” criteria used for proxy selection in MBH98?
  3. Mann et al. state that they use an “objective criterion” to decide how many principal component series to retain for each region and each calculation step. In the SI, they refer to consideration of both Preisendorfer’s Rule N and to a Scree Test but do not state their “objective” criterion. Preisendorfer’s Rule N describes simulations from white noise series. The Supplementary Information to Mann et al.’s second reply describes a simulation process based on red noise modeled with lag-one autocorrelation – a quite different procedure. Can you obtain a provide an exact and replicable description of the procedure used to decide the retention of principal component series?
  4. In the Corrigendum, the use of an 11th site in the SWM group is admitted, but the source of the 11th site is stated only as Stahle, pers. comm., and no location is given. This is unsatisfactory, especially since two sites (yielding 4 series) have  identical values for the first 120-125 years and it appears probable that the Stahle, pers. comm. data is simply a different edition of one of the other sites. Can you please obtain an identification of the location of the Stahle pers. comm. site?
  5. The Corrigendum acknowledges that the citation for instrumental series attributed to Jones and Bradley (1992) was incorrect and stated that the series came from NOAA. There is no additional information in the SI. This new citation does not meet any data citation criteria since NOAA has thousands, if not hundreds of thousands, of different series. Can you please obtain an exact data citation?
  6. Can you please obtain a listing of the 219 gridcells said to have been used in the verification process? We are unable to locate 219 gridcells with continuous data from 1854-1901 in the newly provided temperature data.

Again, we acknowledge that these requests can appear tiresome. But from our perspective, we are only seeking to obtain disclosure of MBH98 data and methods under Nature’s stated policies- in particular that readers should be able to identify the data used and computational procedures applied. We have recently received requests for assistance from other parties, who have developed an interest in replicating the results of MBH98 and have advised them of what we perceive as the principal outstanding issues in obtaining disclosure from Mann et al. 

 

In light of both Nature’s policies, the comments from referees and your own prior commitments, we do not anticipate that there will be any problem in promptly requesting and obtaining the listed information,  especially since some matters have been outstanding for so long. It would be helpful if you were able to provide us with an anticipated schedule so that we have a bring-forward date and do not have to trouble you with repeated requests on this matter.

 

Regards,

Steve McIntyre and Ross McKitrick