A Mistake with Repercussions

The first is: why did it take so long to correct this error, and why did the authors of the original paper not correct it themselves? The error is reasonably easy to spot, even for non-specialists (see addendum). And it was in fact spotted very soon after publication. In January 2005, a comment was submitted to Science which correctly pointed out that Von Storch et al. had calibrated with detrended data and had therefore not tested the Mann et al. method. As such comments are routinely passed to the original authors for a response, Von Storch et al. must have become aware of their mistake at this point at the latest. However, the comment was rejected by Science in May 2005.

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).

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