After 25 years, Mann’s Other Nature Trick Unraveled

Stephen McIntyre has recently again fired up the seminal site for uncovering deficiencies in the works of Mann et al, ClimateAudit.org

His latest post ends a 25 year mystery surrounding the famous MBH98 paper. A Swedish engineer, Hampus Soderqvist, reversed engineered the reconstruction and deduced that:

Mann’s list of proxies  for AD1400 and other early steps was partly incorrect (Nature link now dead – but see  NOAA or here).  Mann’s AD1400 list included four series that were not actually used (two French tree ring series and two Moroccan tree ring series), while it omitted four series that were actually used.  This also applied to his AD1450 and AD1500 steps.  Mann also used an AD1650 step that was not reported.

Soderqvist’s discovery has an important application.

The famous MBH98 reconstruction was a splice of 11 different stepwise reconstructions with steps ranging from AD1400 to AD1820. The proxy network in the AD1400 step (after principal components) consisted 22 series, increasing to 112 series (after principal components) in the AD1820 step.  Mann reported several statistics for the individual steps, but, as discussed over and over, withheld the important verification r2 statistic.  By withholding the results of the individual steps, Mann made it impossible for anyone to carry out routine statistical tests on his famous reconstruction.

However, by reverse engineering of the actual content of each network, Soderqvist was also able to calculate each step of the reconstruction – exactly matching each subset in the spliced reconstruction.  Soderqvist placed his results online at his github site a couple of days ago and I’ve collated the results and placed them online here as well.  Thus, after almost 25 years, the results of the individual MBH98 steps are finally available.

Remarkably, Soderqvist’s discovery of the actual composition of the AD1400 (and other early networks) sheds new light on the controversy about principal components that animated Mann’s earliest realclimate articles – on December 4, 2004 as realclimate was unveiled. Both articles were attacks on us (McIntyre and McKitrick) while our GRL submission was under review and while Mann was seeking to block publication. Soderqvist’s work shows that some of Mann’s most vehement claims were untrue, but, oddly, untrue in a way that was arguably unhelpful to the argument that he was trying to make. It’s quite weird.

Soderqvist is a Swedish engineer, who, as @detgodehab, discovered a remarkable and fatal flaw in the “signal-free” tree ring methodology used in PAGES2K (see X here).  Soderqvist had figured this out a couple of years ago. But I was unaware of this until a few days ago when Soderqvist mentioned it in comments on a recent blog article on MBH98 residuals.

https://climateaudit.org/2023/11/24/mbh98-new-light-on-the-real-data/

The post is a long and technical one to which I cannot do proper justice, and I suggest reading the original at Climate Audit

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