The AMOC, aka the Atlantic Meridional Overturning Circulation, aka the Gulf Stream, aka the ocean currents carrying balmy winds from the warm tropics to northern Europe giving it a warmer climate than its latitude would otherwise permit, is supposed to slow down because climate models say that under greenhouse warming the oceans will yawn and get lazy. Or something: we’ve noted many times that models of the AMOC slowing down have a splendid track record of failure. And now a new study by scientists in Miami and the UK have shown that one of the data sets supposedly supporting the slowing AMOC theory is biased due to, of all things, the Earth’s changing geomagnetic field. After correcting the problem, what used to be a downward trend disappears and the trend since the turn of the century is precisely zero.

The scientific work takes advantage of an underwater telecommunication cable connecting West Palm Beach Florida to the Bahamas, crossing a strait through which flows the Florida Current (FC), one of the main inputs into the Gulf Stream. The varying FC flow rates induce magnetic fluctuations in the cable which have been recorded continuously since 1982, while direct flow measurements in this area have also been collected by ships, floats, sensors dropped from aircraft, and so forth.

The data based on magnetic fluctuations in the communications cable suggest the FC has weakened. The direct measurements did not, an apparent contradiction, but the directly-measured data is more sparse and incomplete so some scientists put more weight on the cable data. Though an additional challenge was that there was a 17-month gap in the cable record from October 1998 to March 2000 because funding for the monitoring equipment dried up. Before the gap, from 1982 to 1998 there was no trend in the data. But afterward, from 2000 to the present, there was a downward trend. So it was the post-2000 trend needing to be explained.

The flow record is based on changes in voltage caused by changing rates of FC flow. But the authors noted that a change in voltage along the cable can also be caused by a shift in the Earth’s magnetic field. The magnetic north pole has been moving in recent decades from the Canadian Arctic towards Russia, somewhat weakening the magnetic flux over the cable. And when the authors adjusted the record for this minuscule change, the trend disappeared:

In the uncorrected data the FC was decreasing by 0.7 sverdrups (Sv) per decade, a sverdrup being a unit of flow of 1 million cubic metres per second named for the Norwegian oceanographer, meteorologist and explorer Harald Ulrik Sverdrup. But after the correction the trend is precisely 0.0 Sv per decade. (Two other data sets, called Dropsonde and LADCP, are also shown in the graph.)

The authors noted that other sources of the AMOC also imply a slowing rate, but when the FC contribution is corrected, the trend in the AMOC as a whole drops from -1.3 Sv per decade to -0.8 Sv per decade, and the whole trend is attributable to a change between 2006 and 2008, with no downward trend since.

We confess a sense of geeky admiration for the scientists who figured out how to measure minute voltage variations in a communications cable and use that to infer flow rates in the ocean above the cable, and also for the scientists who figured out how to correct for the also-minuscule effect of the shifting magnetic north pole. And we express a sense of non-geeky gratitude that the scientists undertook the work and published the results for the world to see even though they didn’t support the model predictions or the climate narrative. Kudos to the authors.