date: Thu, 26 May 2005 09:03:16 -0400 from: "Michael E. Mann" subject: Fwd: RE: NATURE: 2005-02-02202 to: Phil Jones , tim Osborn , Keith Briffa , Scott Rutherford , "Wahl, Eugene R" , Caspar Ammann , mann@virginia.edu Dear All, So here is where we stand w/ the comment. Nature seemed adamant about not allowing us to focus on the synthetic example (ridiculous in my opinion), so I've been forced instead to move this into the Mann et al (pseudoproxy) J. Climate paper. That was in the final stage of revision, but Andrew Weaver has allowed me to add the Moberg-simulation results into the final version since it specifically addresses a request of one of the reviewers of our paper (who wanted to see us discuss implications of the pseudoproxy analyses for the Moberg et al example). I'll send everyone a copy of that when its finalized. They will (see below) allow us to provide some discussion of the synthetic example, referring to the J. Cimate paper (which should be finally accepted upon submission of the revised final draft), so that should help the cause a bit. I'm going to try to produce a revised draft of the Nature comment that confirms to what was outlined by Heike, and then send it to all of you for comments. At that point, we can decide if this is worth submitting, or if it is too flimsy w/out a supporting synthetic example. It would be extremely helpful if Tim or someone else could provide a very simple example (short of model-based pseudoproxies, etc.) that demonstrates the potential for bias we are talking about? I hope to be in touch again soon w/ a revised draft. Meanwhile, feel free to provide me any feedback... thanks, mike X-IronPort-AV: i="3.93,138,1114992000"; d="scan'208,217"; a="36995657:sNHT25392824" From: "Langenberg, Heike" To: "'Michael E. Mann'" Subject: RE: NATURE: 2005-02-02202 Date: Thu, 26 May 2005 10:49:34 +0100 X-Mailer: Internet Mail Service (5.5.2653.19) X-UVA-Virus-Scanned: by amavisd-new at fork3.mail.virginia.edu Dear Mike, thank you for the note. That scenario sounds fine, but please keep the discussion of the synthetic example brief (50-100 words). We will ask the referees whether they think the discussion of the results in the Journal of Climate adds important content to the comment, and if they feel it does, there is no objection from our part. I hope this will clarify our position for you. Best wishes, Heike -----Original Message----- From: Michael E. Mann [[1]mailto:mann@virginia.edu] Sent: 26 May 2005 00:01 To: h.langenberg@nature.com Subject: Re: NATURE: 2005-02-02202 Dear Heike, I'm sorry I've been unable to get back to you sooner. We have chosen to include our synthetic example in the final revisions of our manuscript to be published in "Journal of Climate", and it appears that the manuscript has reached the stage of final acceptance. So this part of our original submitted comment will now appear elsewhere (J. Climate) and obviously it would be inappropriate for us to publish those results again in Nature. Therefore, including this in our comment is a moot issue now. So, if we chose to revise our original submitted comment along the lines you have suggested in your email below, focusing on the application to the Mann and Jones (2003) dataset & demonstration that the procedure inherently inflates the low-frequency variability (and eliminating the latter part of the comment which focuses on the synthetic example), would there be any objection on Nature's part to us briefly discussing the synthetic network results in the context of the comment, referring to our manuscript accepted in Journal of Climate for further details? We're very much hoping that this is a scenario with which Nature would be comfortable. I thanks in advance for your response, Mike At 11:47 AM 5/10/2005, h.langenberg@nature.com wrote: Content-Disposition: inline Content-Length: 4973 Content-Transfer-Encoding: binary Content-Type: text/plain Dear Mike, thank you for the note, asking for clarification of our decision. However, I am afraid I am unable to follow your argument and therefore suggest that you revise your contribution along the lines indicated in our previous letter, if you wish to pursue publication in Nature. Specifically, both referees feel that a quantification of the possible bias in the Moberg et al estimate of low-frequency variability based on your synthetic example (the second part of your manuscript) is flawed or at least highly uncertain given the assumptions that go into your reconstruction (as, for example, outlined in referee 1's point 1). Based on these criticisms, we decided to decline publication of the present version of the comment, and I am sorry to say that we are unable to conclude that your remarks below address these criticisms satisfactorily. However, referee 2 notes that you identify a weakness in the Moberg et al approach (that is, that they normalise the data before filtering). We offered the possibility to resubmit specifically because we feel that this point (if significant) may be of interest to our broader audience. It seems to us that the referee's suggestion of providing a direct comparison between the Moberg reconstruction and results obtained with the same method but after correction of this weakness would be the most convincing quantification of its effect. I hope these comments will help to clarify our decision and help you decide how best to proceed. Best wishes, Heike -----Original Message----- From: Michael E. Mann [[2]mailto:mann@virginia.edu] Sent: 06 May 2005 19:58 To: h.langenberg@nature.com Subject: Re: Decision on Nature Manuscript 2005-02-02202 Dear Heike, Thanks for your email. We would be happy to revise our contribution for consideration by Nature. However, let me first seek some further clarification from you. Your email indicates that our revised comment should quantify "the spurious contribution to long-term variability introduced in the Moberg et al. reconstruction due to the erroneous normalising procedure prior to the filtering process". This is indeed what we felt we were doing, but apparently this was not communicated as clearly as it needed to be. In particular, your email suggests that our revised version eliminate the latter half of the contribution (the synthetic proxy or "pseudoproxy" analysis). This is problematic, because this is actually where the key scientific points are made, and where general conclusions about the potential bias of the method can be drawn. The first half of our contribution simply shows that using the Moberg et data data applied to the Mann and Jones (2003) reconstruction inflates the low-frequency variance. It does not (nor can it) address whether or not the inflation of variance is realistic or not. The reviewers are in fact incorrect when they conclude that this part of our analysis demonstrates a bias in the Moberg et al method. It doesn't! Only an analysis (as described in the second half of our comment) in which the exact answer is known, so that competing methods can be objectively tested against a "ground truth", can address whether the additional variance is spurious or not. In other words, with a synthetic example, where, unlike the real world, the actual climate history is known, we can determine whether or not a particular method returns the correct reconstruction. This was described in some detail in the supporting manuscript we provided, which was presumably seen by the reviewers? But the reviewers, at least in part, fail to have grasped this key point. In the synthetic example, we showed that the Moberg et al method does not return the actual model history when applied to realistic synthetic proxies. So there can be no question that the method exhibits a bias. Its purely a matter of how *large* the bias is. We feel that this point has somehow been lost on the reviewers. The degree of bias does indeed depend on signal-to-noise ratios, and we can easily quantify that in a revised comment. Part of the confusion (at least with reviewer #2) appears to have been with our Figure 3 which left out one important piece of information (the uncertainty in the Moberg et al-type reconstruction). That is easily rectified as well. So we would like to request that we not drop the synthetic proxy or "pseudoproxy" aspect of the analysis, which is absolutely essential to the argument we are making, but instead revise this part of the analysis to address the criticisms raised by the original authors, and to clarify precisely what is shown by such a synthetic example. In the process, we would we would quantify, as requested, the dependence of the bias on e.g. signal-to-noise characteristics of the pseudoproxy data. Please let me know if it would be acceptable for us to proceed as suggested above. Thanks in advance, Mike This email has been sent through the NPG Manuscript Tracking System NY-610A-NPG&MTS ______________________________________________________________ Professor Michael E. Mann Department of Environmental Sciences, Clark Hall University of Virginia Charlottesville, VA 22903 _______________________________________________________________________ e-mail: mann@virginia.edu Phone: (434) 924-7770 FAX: (434) 982-2137 [3]http://www.evsc.virginia.edu/faculty/people/mann.shtml ******************************************************************************** DISCLAIMER: This e-mail is confidential and should not be used by anyone who is not the original intended recipient. If you have received this e-mail in error please inform the sender and delete it from your mailbox or any other storage mechanism. 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Mann Department of Environmental Sciences, Clark Hall University of Virginia Charlottesville, VA 22903 _______________________________________________________________________ e-mail: mann@virginia.edu Phone: (434) 924-7770 FAX: (434) 982-2137 [4]http://www.evsc.virginia.edu/faculty/people/mann.shtml