A recent, highly-publicized article by Stefan Rahmstorf and the notorious Michael Mann claimed that the Gulf Stream is slowing down due to global warming, with potentially significant consequences for northern Europe. Rahmstorf describes the article:
Climate models have long predicted such a slowdown – both the current 5th and the previous 4th IPCC report call a slowdown in this century “very likely”, which means at least 90% probability. When emissions continue unabated (RCP8.5 scenario), the IPCC expects 12% to 54% decline by 2100 (see also the current probabilistic projections of Schleussner et al. 2014). But the actual past evolution of the flow is difficult to reconstruct owing to the scarcity of direct measurements.
So they didn’t actually measure the flow of the Gulf Stream. Rather, they confirmed what their models predict through…proxies!
What is new is that we have used proxy reconstructions of large-scale surface temperature (Mann et al, 2009) previously published by one of us (study co-author and RealClimate co-founder Mike Mann) that extend back to 900 AD (see “What we can learn from studying the last millennium (or so)”) to estimate the circulation (AMOC) intensity over the entire last 1100 years (Fig. 3).
It turned out, however, that some people actually have measured Gulf Stream flow for a considerable time:
[N]one of the studies include any direct measurements of the current over an extended period to prove their point.
But this is exactly what has been underway at the University of Rhode Island and Stony Brook University for the last 20 years: measurement of the strength of the Gulf Stream. And according to a paper published in Geophysical Research Letters, the researchers find no evidence that the Gulf Stream is slowing down. These new results reinforce earlier findings about the stability of Gulf Stream transport based on observations from as far back as the 1930s. …
“The ADCP measures currents at very high accuracy, and so through the repeat measurements we take year after year, we have a very powerful tool by which to monitor the strength of the current,” said Rossby. “There are variations of the current over time that are natural — and yes, we need to understand these better — but we find absolutely no evidence that suggests that the Gulf Stream is slowing down.”
This is typical: global warming alarmism is based on models, not data, and when the data contradict the models, the alarmists ignore the data. But it gets even worse, as Steve McIntyre explains at Climate Audit:
The new article by Rahmstorf and Mann has been criticized at WUWT for making claims about Atlantic Ocean currents based on proxies, rather than measurements. 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 [one of the leading global warming alarmists] 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[st] 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? …
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?
The blunt truth is that climate alarmism isn’t science at all. It is a combination of politics, religion and–perhaps most of all–financially self-interested hucksterism.