Washington Post: North Atlantic Current Continues to Decline
February 26, 2021
A growing body of evidence suggests that a massive change is underway in the sensitive circulation system of the Atlantic Ocean, a group of scientists said Thursday.
The Atlantic meridional overturning circulation (AMOC), a system of currents that includes the Florida Current and the Gulf Stream, is now “in its weakest state in over a millennium,” these experts say. This has implications for everything from the climate of Europe to the rates of sea-level rise along the U.S. East Coast.
Although evidence of the system’s weakening has been published before, the new research cites 11 sources of “proxy” evidence of the circulation’s strength, including clues hidden in seafloor mud as well as patterns of ocean temperatures. The enormous flow has been directly measured only since 2004, too short a period to definitively establish a trend, which makes these indirect measures critical for understanding its behavior.
The new research applies a statistical analysis to show that those measures are in sync and that nine out of 11 show a clear trend.
Prior research had suggested that the AMOC was at its weakest point in a millennium or more, and suggested a roughly 15 percent weakening since about 1950. But when it comes to the latest evidence, “I think it just makes this conclusion considerably stronger,” said Stefan Rahmstorf, an author of the research and an oceanographer with the Potsdam Institute for Climate Impact Research in Germany.
The study was published in Nature Geoscience by scientists from the Potsdam Institute, Ireland’s Maynooth University and University College London.
The AMOC is driven by two vital components of ocean water: temperature and salt. In the North Atlantic, warm, salty water flows northward off the U.S. coastline, carrying heat from the tropics. But as it reaches the middle latitudes, it cools, and around Greenland, the cooling and the saltiness create enough density that the water begins to sink deep beneath the surface.
The water then swings back southward and travels all the way to the Southern Hemisphere, submerged, where it makes its way to the Antarctic as part of a global system of ocean currents. The entire system is known as the ocean’s thermohaline circulation (“thermo” meaning heat and “haline,” salt), and it plays many critical roles in the climate. It is also referred to as the global ocean conveyor belt, because it redistributes heat worldwide.
In the North Atlantic, most important is the transport of heat northward, which has a moderating effect on Europe’s climate in particular. But the circulation can be weakened by making northern water more fresh and less salty, and therefore less dense. That’s what climate change — through a combination of more rain and snow, more melting of Arctic sea ice, and huge freshwater pulses from Greenland — is thought to be doing.
The AMOC has captured the popular imagination because of its depiction in the lurid sci-fi film “The Day After Tomorrow,” in which various disastrous events occur after a sudden halting of the current. Nothing nearly so dire is underway, and scientists say that although a shutdown is possible in the future as climate change continues, steady weakening is the more likely course in the near future.
The late climate scientist Wallace S. Broecker wrote in 1997 that the AMOC is the “Achilles’ heel” of the climate system, citing evidence that it has switched on and off repeatedly over the course of Earth’s history, with the power to flip warming periods to intense cold in the Northern Hemisphere.
Scientists do not expect anything so severe in our future, especially because greenhouse gases will continue to cause offsetting warming. However, they note that even the modest slowing of 15 percent has been accompanied by odd temperature patterns in the ocean and the significant upending of certain key fisheries, such as lobster and cod off the coast of New England.
In particular, a recurrent “cold blob” has been observed in the ocean to the south of Greenland — a large region that is bucking the overall global warming trend and instead showing a marked cooling pattern. Scientists think this is evidence that less warm water is reaching this region than previously, and that it may also be a result of runoff from the melting ice sheet.
At the same time, warm water has lingered instead off the coast of the northeastern United States, where the Gulf of Maine is showing some of the fastest-warming ocean water anywhere in the world.
Climate Denial Crock of the Week 
February 26, 2021 at 1:41 pm
February 26, 2021 at 6:53 pm
Not that it matters to the social aspect but the AMOC doesn’t actually go to the Antarctic if that means Antarctica. The A25 salinity profile clearly shows at least a part of it lifting the Atlantic Ocean above at 45-55 S or some such (from memory). Those cartoons are very sketchy and a real dog’s breakfast showing quite a varied eclectic mix.
February 28, 2021 at 7:12 pm
A25 S.B. A16 (it’s at 25W)
February 26, 2021 at 8:00 pm
“the Northern Hemisphere suddenly became much colder”. “flip warming periods to intense cold in the Northern Hemisphere”. I seriously doubt that 50% of the tropics suddenly became much colder.
February 27, 2021 at 8:10 pm
the baked-in warming that we already have would greatly mitigate northern cooling, I am told.
March 18, 2021 at 8:44 am
Your comment is a non-sequitor to mine so should be posted standalone rather than as a pretense of commenting on my comment.
February 26, 2021 at 10:18 pm
The AMOC is part of the global thermohaline ocean circulation system and certainly a drastic slowdown of this current would have drastic climatic implications.
“North Atlantic Deep Water is primarily upwelled at the southern end of the Atlantic transect, in the Southern Ocean. This upwelling comprises the majority of upwelling normally associated with AMOC, and links it with the global circulation.] On a global scale, observations suggest 80% of deepwater upwells in the Southern Ocean.” – Atlantic meridional overturning circulation (wikipedia)
AMOC disruption has featured high on Climate tipping point warning charts & systems for many years now, and if we allow it to happen – it would cause an abrupt climate change.
“Rapid melting of the Greenland ice sheet and further slowdown of the AMOC could destabilize the West African monsoon, triggering drought in Africa’s Sahel region. A slowdown in the AMOC could also dry the Amazon, disrupt the East Asian monsoon and cause heat to build up in the Southern Ocean, which could accelerate Antarctic ice loss.”
https://www.nature.com/articles/d41586-019-03595-0
February 26, 2021 at 10:25 pm
Potsdam Institute estimate on our current course – the AMOC would be seriously disrupted at the end of this century.
“If we continue to drive global warming, the Gulf Stream System will weaken further – by 34 to 45 percent by 2100 according to the latest generation of climate models,“ concludes Rahmstorf. “This could bring us dangerously close to the tipping point at which the flow becomes unstable.”
https://www.pik-potsdam.de/en/news/latest-news/gulf-stream-system-at-its-weakest-in-over-a-millennium
others are less specific on the timescale but indicate it could be sooner.
This is why people are calling it a climate emergency.
“Researchers from the University of Copenhagen – who conducted the study – said their model indicates the AMOC could reach a “tipping point” or, crucial threshold, sooner than earlier predicted because of the speed at which glacial ice is melting. ”
https://www.voanews.com/science-health/new-study-suggests-atlantic-ocean-circulation-system-could-collapse
March 2, 2021 at 7:15 pm
Exactly. In climate science, the only constant condition is faster-then-expected. I keep calling for emergency actions and keep getting ignored or criticized by people who don’t seem to understand the basic concept of faster-than-expected.
And if the situation is dire, the actions called for are emergency actions, too. Since the people in power aren’t willing to take emergency action, the people in power have to be removed from power, by whatever peaceful means are necessary. That includes the oligarchic Democrats, who are still unwilling to consider even serious non-emergency actions. Removing the POG, getting rid of the filibuster, statehood for DC and PR, packing the court(s), initiating a crash program to build a national-and-beyond high speed rail network (and a rail network, for that matter), enabling/mandating multi-energy 2-axis tilting solar panels, starting up Manhattan-like projects to solve steel, concrete, plastics, deep ocean wind turbines, and a bunch of other stuff,
And frgoking CALLING IT AN EMERGENCY! OFFICIALLY!
February 26, 2021 at 10:30 pm
Government research bodies concur the danger is present and growing.
“Freshwater outflow from Beaufort Sea could alter global climate patterns”
“However, the modeled release was based on freshwater volumes of the past, from the 1990s. Now, that volume is significantly greater, more than 23,300 cubic kilometers, owing to an unusually persistent circulation pattern called the Beaufort Gyre and to unprecedented sea ice decline. If this very large volume of freshwater is released into the North Atlantic, the impacts could be correspondingly very large as well. The exact impact is still unknown. “Our study of the previous release event offers a picture into the potential impacts of a future, larger release,” Weijer said.”
https://www.lanl.gov/discover/news-release-archive/2021/February/0224-beaufort-sea.php
February 27, 2021 at 3:31 am
Maybe this is just one of the many oscillations climatologist have found in the past decades.
February 27, 2021 at 11:57 am
Oh ok, I feel much better now. It is just a normal oscillation, nothing to see, keep on walking by, don’t look back,…
February 27, 2021 at 1:21 pm
In case you foolishly thought “The Day After Tomorrow” was not a documentary.
March 18, 2021 at 8:42 am
Continuing from my prior relevant science note that the AMOC doesn’t actually go to the Antarctic as incorrectly stated in this article, in one of the recent scientist talks I’ve viewed I’ve come across a better-than-average pictorial indicating that AMOC stops and lifts some region of the South Atlantic Ocean at 40 S or thereabouts (as opposed to my 45-55 S from old memory), so ~3,300 km north of Antarctica.
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Incidentally, it also shows the route of section A16 at 25W of 1990 WOCE where I got my original salinity profile information from 8 years ago.
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It’s at 1:51 at https://www.youtube.com/watch?v=eV-g4_2Xwn8