Extreme Temperature Diary- Friday February 26th, 2020/ Main Topic: Growing Evidence That The Atlantic Meridional Overturning Circulation (AMOC) Is Slowing

The main purpose of this ongoing blog will be to track worldwide extreme record temperatures related to climate change. Any reports I see of ETs will be listed below the main topic of the day. I’ll refer to extreme or record temperatures as ETs (not extraterrestrials).😉

Main Topic: Growing Evidence That The Atlantic Meridional Overturning Circulation (AMOC) Is Slowing

Dear Diary. Any good 7th or 8th grade student can tell you that both the atmosphere and oceans are fluids which interchange heat, so it’s no surprise that both are warming due to carbon pollution. In turn, the atmosphere’s added warmth is affecting ocean circulations. Most of these control and regulate the flow of heat from the equator to the poles and vice a versa, being a big part of our natural Earth climate system. One important ocean loop is the Atlantic Meridional Overturning Circulation or (AMOC).

We’ve had hints that the AMOC has been slowing since late last century. Now we have more evidence that this circulation has been slowing due to carbon pollution. For many more details and the effects of this change, please read the following Washington Post article:


Climate and Environment

Scientists see stronger evidence of slowing Atlantic Ocean circulation, an ‘Achilles’ heel’ of the climate

The Atlantic meridional overturning circulation, a system of currents, is weaker than it has been in 1,000 years

Skogafoss waterfall is pictured near Skogar in Iceland. The country’s climate is more temperate than in other regions that far north because of the influence of the warm Gulf Stream current. (Maja Hitij/Bongarts/Getty Images)

By Chris Mooney and Andrew Freedman Feb. 25, 2021 at 8:00 a.m. PST

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 crumbled foundation of a house that used to sit along the water in South Kingstown, R.I. Disruptions in the Gulf Stream could lead to increased sea levels. (Salwan Georges/The Washington Post)

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.

Global temperature anomalies in 2020, according to the National Oceanic and Atmospheric Administration, showing the recurrent “cold blob” south of Greenland. (NOAA)

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.

Michael Mann, a climate scientist at Penn State who co-wrote a major 2015 study with Rahmstorf showing a slowing AMOC, said the cold blob has been “remarkable” in its staying power.

Mann said that the cold blob’s presence since 2015 has helped convince him that the ocean current’s slowdown is a robust finding. “The remarkable persistence of the cold blob since the publication of our article has convinced me, ‘Yeah, it’s real.’ ”

At the same time, though, the latest study does rely on “proxy evidence,” rather than direct measurements of the circulation.

To give an example, one of the proxy-based studies, published last year, uses sediment collected from the seafloor to the south of Iceland, and the microscopic organisms it contains, to detect a shifting of water types over time. It therefore infers more warm water arriving in recent decades as opposed to colder conditions over hundreds of previous years.

The current study’s conclusions are, by necessity, only as good as the proxies are. And the complexity of different currents in the Atlantic, as well as different definitions of the AMOC, can call into question what the proxies are actually measuring, said Marilena Oltmanns, an oceanographer at the National Oceanography Center in Britain.

Still, Oltmanns noted, “I think it is commendable that the authors used so many different proxies. So, even if only one of these proxies is linked to the AMOC, it should be sufficient to justify their conclusion.”

Rahmstorf understands the concern but thinks the big picture nevertheless presents a major shift.

“The proxies from different regions are measuring different aspects of a complex 3-D AMOC circulation,” he said. “To me, the key is that all these pieces of the AMOC puzzle fit together so nicely in the proxy data.”

Headshot of Chris Mooney

Chris Mooney is a Pulitzer Prize winning reporter covering climate change, energy, and the environment. He has reported from the 2015 Paris climate negotiations, the Northwest Passage, and the Greenland ice sheet, among other locations, and has written four books about science, politics and climate change. Follow

Headshot of Andrew Freedman

Andrew Freedman edits and reports on extreme weather and climate science for the Capital Weather Gang. He has covered science, with a specialization in climate research and policy, for Axios, Mashable, Climate Central, E&E Daily and other publications. Follow

Here are other takes on this important topic:

Here are some “ET’s” reported from Friday:

Here is more climate and weather news from Friday:

(As usual, this will be a fluid post in which more information gets added during the day as it crosses my radar, crediting all who have put it on-line. Items will be archived on this site for posterity. In most instances click on the pictures of each tweet to see each article. The most noteworthy items will be listed first.)

Now here are some of today’s articles and notes on the horrid COVID-19 pandemic:

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Guy Walton “The Climate Guy”

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