Steve McIntyre’s analysis of contaminated data used by Mann et al 2008 demonstrates that relevant criteria for retraction has been met based on PNAS publication policy.
From time to time, scientists inadvertently use contaminated data and their results are affected. For example, some time after publication of Grand et al (PNAS 2004), the authors determined that their results were erroneous as a “result of contamination of genomic DNA with plasmid DNA”. They promptly issued a retraction, expressing their regret for the error and any inconvenience. The reputation of the authors does not appear to have been diminished by the retraction. Mistakes happen and the mistake was promptly dealt with by retraction of the article.
Like Grand et al, Mann et al 2008 (M08) used contaminated data, in their case, the Finnish sediment data of Tiljander et al, the modern portion of which had been contaminated by agriculture and bridgebuilding. In addition to using the modern contaminated portion of the data, M08 made a second error by using the Tiljander lightsum and XRD upside down to the interpretation of its originators. Their handling of Tiljander data has been sharply criticized on different occasions by two eminent Finnish paleolimnologists – Atte Korhola here and Matti Saarnisto here.
In contrast to Grand et al, Mann et al have not issued a retraction or corrigendum or even admitted an error. Instead, in multiple venues (without explicitly admitting an error), they’ve asserted that, in any event, the error doesn’t affect their “central conclusions” [their PNAS reply, Feb 2009 here] or, more recently, “any” of their conclusions [Mann et realclimate, June 2011 here], as though that ended the matter.
It doesn’t. Even if the error didn’t have a material impact on the results, a Corrigendum should have been issued. Kaufman et al 2009, for example, issued a corrigendum when they learned that they too had used data (including their Tiljander series) upside down. But the situation for Mann et al 2008 is quite different. The most prominent claim for Mann et al 2008 was its supposed achievement of a “skillful” reconstruction without tree rings for the past 1300 years. Unfortunately, this “achievement” can now be seen to have been a complete mirage, dependent on the use of contaminated data in the EIV reconstruction without tree rings.
In the realclimate response to controversy over the Yamal proxy in September 2009, for example, the EIV no-dendro reconstruction of M08 was put forward as a supposed repudiation of Climate Audit:
Oh. The hockey stick you get when you don’t use tree-rings at all (blue curve)?
It has subsequently become a staple in public defence of the Stick, e.g. Skeptical Science here and here and numerous others. All such assertions rely on the supposed “skill” of the M08 EIV reconstruction. Unfortunately, the “achievement” was an illusion, as Mann et al quietly admitted in the SI to Mann et al 2009.
PNAS Policies on Retraction and SI
PNAS has the following policy on corrections and retractions:
PNAS publishes corrections for errors, made by the journal or authors, of a scientific nature that do not alter the overall basic results or conclusions of a published article. PNAS publishes retractions for major errors that may call into question the source of the data or the validity of the results and conclusions of an article. Errata are published at the discretion of the editors and appear as formal printed and online notices in the journal.
The use of contaminated sediments in M08 was, at a minimum, an “error”. This has been clearly stated by Finnish paleolimnologists Korhola and Saarnisto. Kaufman et al 2008, of which Bradley was a co-author, have already acknowledged a lesser error and issued a corrigendum.
As shown above, despite claims to the contrary, the error has a major impact on the EIV reconstruction without tree-rings and its verification statistics, both of which were relied on in the M08 assertion that they had achieved a “skillful” reconstruction without tree rings for the past 1300 years.
As noted in the lead paragraph, scientists sometimes use contaminated data. If science is to be “self-correcting”, then scientists actually have to issue corrections and, if necessary, retractions. As the example of Grand et al 2004 shows, this actually happens from time to time, but life goes on.
So too here. Mann et al 2008 meets relevant PNAS criteria for retraction. Hopefully, either PNAS or the authors will see the wisdom of retracting the article before it gets used by IPCC AR5.
Full post here: Dirty Laundry II: Contaminated Sediments
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