Steve McIntyre: Reductio Ad Mannium
Using Mannian RegEM with the Mann et al 2008-9 network of 1209 “proxies”, one can probably “reconstruct” almost anything. Are you interested in “reconstructing” the medieval Dow Jones Index? Or medieval NFL attendance?
The new article by Rahmstorf and Mann (see RC here) has been criticized at WUWT (here here) for making claims about Atlantic Ocean currents based on proxies, rather than measurements. (Also at Judy’s here) But it’s worse, much worse than we thought.
Rahmstorf and Mann’s results are not based on proxies for Atlantic current velocity, but on a network consisting of contaminated Tiljander sediments (upside-down or not), Graybill’s stripbark bristlecone chronologies, Briffa MXD series truncated to hide-the-decline and hundreds of nondescript tree ring series statistically indistinguishable from white noise. In other words, they used the same much-criticized proxy network as Mann et al 2008-9. It’s hard to understand why anyone would seriously believe (let alone publish in peer reviewed literature) that Atlantic ocean currents could be reconstructed by such dreck, but Rahmstorf et al 2015 stands as evidence to the contrary.
After so much controversy about Mann’s prior use of contaminated data, it defies credulity that he and Rahmstorf have done so once again.
And when the National Research Council panel recommended in 2006 that stripbark bristlecone chronogies be “avoided” in temperature reconstructions, they can scarcely have contemplated (let alone, endorsed) their use in reconstruction of Atlantic ocean currents.
Seemingly leaving no stone unturned, the Rahmstorf and Mann dataset even truncates the Briffa MXD chronologies in 1960, thereby hiding the decline (see here for a discussion of MXD truncation in Mann et al 2008 in September 2008, long before we learned from Climategate emails that they were using a trick to “hide the decline”)