Was Preisendorfer’s Rule N Used in MBH98 Tree Ring Networks?

Mann et al. have recently argued that they can salvage MBH98-type results, even with correct PC calculations by also using “the standard selection rule (Preisendorfer’s Rule N) used by MBH98″. They say that this method permits them to retain 5 PCs in the North American network. The reason why this matters to them is that the bristlecones are represented in the PC4 in correct PC calculations and the expanded roster would permit them to imprint the NH temperature reconstruction even from the PC4 position.

We have discussed elsewhere many issues regarding the robustness and statistical significance of this calculation, arguing that the bristlecones are not a valid proxy, that the MBH98 reconstruction is not robust to the presence/absence of the bristlecones and the MBH98 reconstruction has no statistical significance in its early portion. Here I consider the narrow issue of whether the PC selection method illustrated in the Nov. 22, 2004 diagram was actually “used by MBH98″ for tree ring networks.

I have been able to closely replicate the Nov. 22, 2004 diagram published at realclimate.org – which is now said to demonstate the PC selection method used in MBH98 (although this method was not reported in MBH98). I have tested the 19 network/calculation step combinations used in MBH98 to verify the archived PC selections at the Corrigendum SI against this diagram.

In 18 of 19 cases, the selections from the Preisendorfer-type calculation are inconsistent with the the Corrigendum SI archive. In some cases, more PCs are selected; in some cases, fewer. In 3 calculations, different selections are taken from the same network in different calculation steps – a result inconsistent with the stated policy.

This is strong evidence that the method of the Nov. 22, 2004 diagram, as illustrated and without still undisclosed modifications, was not used to determine the number of retained PCs in MBH98. We believe that climate scientists, who have relied on MBH98, should ask Nature and/or the U.S. National Science Foundation to require the disclosure of all source code used in MBH98, including the selection of PC series.

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3 Comments

  1. Louis Hissink
    Posted Feb 7, 2005 at 4:05 PM | Permalink

    Hi Stephen,

    Welcome to the blogging world! The Bre-X articles are spot on, in more ways one could imagine.

  2. Louis Hissink
    Posted Feb 7, 2005 at 4:29 PM | Permalink

    Hi Steve,
    Great to see you blogging at last. The comments about Bre-X is an extremely important consideration.

  3. TCO
    Posted Sep 11, 2005 at 9:54 AM | Permalink

    The Preisendorfer thing seems to come accross as an after the fact justification. They didn’t really use it. And they didn’t describe it’s use in their discussion of methods in the paper.

    It’s still unclear to me what PCA really is and if having a PC4 that is sticky shaped means anything. Surely it is the total summation that matters, no?

    And I also don’t get the deal with needing to do linear interpolation and other data addition to make the method work. Surely there is some transform that does not depend on this type of activity. And additionally, does addition of data like this mean that some series are effectivly over-represented in significance?

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