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”)
In 2002, even Keith Briffa was frustrated enough by the Mann et al 1998 reconstruction to observe:
I am sick to death of Mann stating his reconstruction represents the tropical area just because it contains a few (poorly temperature representative ) tropical series. He is just as capable of regressing these data again any other “target” series , such as the increasing trend of self-opinionated verbage he has produced over the last few years , and … (better say no more)
But at least the network that Briffa complained about contained a “few poorly temperature representative” tropical series. Rahmstorf et al 2015 dispensed with even that meager precaution by purporting to reconstruct Atlantic ocean currents without using any proxies purporting to directly measure Atlantic ocean current.
What is one to say of a climate science field which permits such practices to continue unchecked? Should one borrow Andrew Weaver’s words and say:
They let these random diatribes of absolute, incorrect nonsense get published. They’re not able to determine if what’s being said is correct or not, or whether it’s just absolute balderdash.
Whatever may or may not be happening with the Atlantic Meridional Overturning Current (AMOC), one thing that you can take to the bank (or insane asylum, as appropriate): contaminated Finnish lake sediments, strip bark bristlecone pines and the hundreds of nondescript Mann 2008-9 tree ring series do not contain any useful information on the past history of the AMOC.
Only one thing can be surmised from Rahmstorf and Mann’s claim that the Mann et al 2008-9 network can be used to reconstruct not just NH temperature, but also SH temperatures and now Atlantic Meridional Overturning Circulation: 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?
Reduction ad mannium.
Postscript: unsurprisingly, Rahmstorf et al has many interesting booby traps. As homework questions. (1) why is the most recent value of the gyre reconstruction shown in Rahmstorf Figure 3 (middle panel) ends in approximately 1995, when the underlying gridded reconstruction of Mann et al 2009 goes to 2006. (2) why are the reconstructions only shown back to AD900, when the underlying gridded reconstruction of Mann et al 2009 begins in AD500.