A Mistake with Repercussions

In a paper dated July 2005, Zorita and Von Storch admit their error in passing, writing: “the trend is subtracted prior to the fit of the MBH regression/inflation model (von Storch et al. 2004). […] It seems, however, that MBH have exploited the trends”. It is thus clear that they knew that their central claim of the Science paper, namely that they had tested the Mann et al. method, was false. But rather than publishing a correction in Science, they wrote the above in a non-ISI journal called “Memorie della Societa Astronomica Italiana” that not many climatologists would read.

An unambiguous correction in Science, where the original paper appeared, would not only have been good scientific practice. It would have been particularly important given the large public and political impact of their paper. It would have been a matter of courtesy towards their colleagues Mike Mann, Raymond Bradley and Malcolm Hughes, who had suffered a major challenge to their scientific reputations as well as having to invest a large amount of time to deal with the Congressional enquiry mentioned above. And it would have been especially pertinent given the unusually vitriolic media statements made previously: in an interview with a leading German news magazine, Von Storch had denounced the work of Mann, Bradley and Hughes as “nonsense” (“Quatsch”). And in a commentary written for the March 2005 German edition of “Technology Review”, Von Storch accused the journal Nature for putting their sales interests above peer review when publishing the Mann et al. 1998 paper. He also called the IPCC “stupid” and “irresponsible” for highlighting the results of Mann et al. in their 2001 report.

There were at least two further issues with the Von Storch et al. paper:

– The model run of Von Storch et al. suffers from a major climate drift due to an inappropriate initialisation procedure. Despite starting in medieval times, the model was initialised from a present-day, rather than pre-industrial, climate state – i.e. from a climate affected by human-caused warming. As a result, the Northern Hemisphere temperature in the model drops by about 1.5 ÂșC during the initial 100-year adjustment phase and keeps drifting down for the coming centuries. This problem is never mentioned and this part of the experiment is not shown in publications, although climate modellers know that such severe disequilibrium must cause a long-lasting climate drift in the remainder of the run. After Osborn et al. (2006) documented this problem, Von Storch et al. repeated their experiment with improved initialisation. Their new run shows that about half the cooling from medieval times to the 19th Century in their original paper was due to this artificial drift, but again they have not published a correction or demonstrated the impact of this issue (see addendum).

– Von Storch et al. also looked at another model, stating: “Similar results are obtained with a simulation with the third Hadley Centre coupled model (HadCM3), demonstrating that the results obtained here are not dependent on the particular climate characteristics of the ECHO-G simulation.” They have repeatedly made similar claims in the media. This is important, as any model result is considered somewhat preliminary until confirmed with an independent model. However, their statement appears to us to be a serious misrepresentation of the HadCM3 results which were shown only in the online supplement to their paper (see addendum).

In their response to the Wahl et al critique, Von Storch et al acknowledge the original problem but in order to salvage their result, they introduce a large ‘red noise’ component into the proxies. This changes the nature of their test and implies an ‘a priori’ loss of low frequency variance instead of trying to calculate whether a particular methodology produces such a loss.

One could view this story as a positive example for the self-correcting process of science: erroneous results are eventually spotted and corrected, even if it sometimes takes time. If only science were at stake here, we’d need say no more: this would have been a sometimes inappropriately sharp, but otherwise regular technical debate about improving the methodology of proxy reconstructions.

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