The Daily Populous Tuesday January 28th, 2025 morning edition
Authored by whoi.edu and submitted by ahothabeth

Atlantic Meridional Overturning Circulation (AMOC) helps to regulate the Earth’s climate and weather

Images available for use with credit can be found here.

Woods Hole, Mass. (January 15, 2025) — Earth, being 71 percent covered in water, is influenced by the ocean and its movements. In the Atlantic Ocean, a system of connected currents, called the Atlantic Meridional Overturning Circulation (AMOC), moves water throughout the world’s oceans powered by a combination of winds and ocean density. It not only distributes the ocean’s heat, moisture, and nutrients, but regulates the Earth’s climate and weather.

As the climate is continuously changing and the atmosphere is warming, many scientists fear that fresh water from melting polar ice sheets could significantly disrupt—or collapse—the AMOC. While a decline of the AMOC would have grave consequences, a collapse would be truly catastrophic. However, studies about the AMOC’s long term future are uncertain. Instead of predicting the future, a team of scientists from Woods Hole Oceanographic Institution (WHOI) quantified the past to help inform where we could be going.

In a new paper published in Nature Communications, scientists found that the AMOC has not declined in the last 60 years. Authors Nicholas P. Foukal, adjunct scientist in Physical Oceanography at WHOI and assistant professor at the University of Georgia; Jens Terhaar, affiliated scientist at WHOI and senior scientist at the University of Bern; and Linus Vogt, visiting student at WHOI when he started to work on this study and now scientist at LOCEAN, Sorbonne Université, say their results mean that the AMOC is currently more stable than expected.

“Our paper says that the Atlantic overturning has not declined yet,” Foukal said, who conducted the research while at WHOI. “That doesn’t say anything about its future, but it doesn’t appear the anticipated changes have occurred yet.”

Their findings contrast with previous work, notably a paper from 2018 cited in their study, which reported that the AMOC has declined over the last 70 years. This past work relied on sea surface temperature measurements to understand how the AMOC has changed, but “we’ve learned that sea surface temperature doesn't work as well as initially thought,” said Terhaar, who began leading this study at WHOI as a postdoctoral scientist and completed the work in Bern.

To address the uncertainty, Terhaar and the team relied on new data from the Coupled Model Intercomparison Project (CMIP), climate-earth models produced by the World Climate Research Program. They used 24 different CMIP models and found that the most recently available surface temperature data did not accurately reconstruct the AMOC. To go a step further, the researchers looked at a different measure: air-sea heat fluxes, which is the exchange of heat from the ocean to the atmosphere. When the AMOC is stronger, more heat is released from the ocean to the atmosphere over the North Atlantic.

The authors derived this AMOC proxy with the CMIP models, then applied it to observational data. The best data for surface heat fluxes over the North Atlantic come from reanalysis products that incorporate direct observations into a model, similar to the way weather forecasts work. The study authors focused on two reanalysis data sets that extend back to the late 1950s to reconstruct the AMOC.

“Based on the results, the AMOC is more stable than we thought,” Vogt said. “This might mean that the AMOC isn’t as close to a tipping point as previously suggested.”

The paper states that air-sea heat flux anomalies in the North Atlantic are tightly linked to the AMOC and that “the decadal averaged AMOC has not weakened from 1963 to 2017.” Since there are many processes that lead to large year-to-year variability in the AMOC, the air-sea heat flux and the AMOC are correlated strongest at those timescales, as opposed to annual averages.

“It’s almost unanimous at this point that the Atlantic overturning will slow in the future, but whether or not it will collapse is still up for debate,” Foukal said. “This work indicates that there is still time to act before we reach this potential tipping point.”

As with all proxy-based reconstructions, there are limitations and caveats. The authors point out that direct measurements of air-sea heat flux going back in time are sparse, and thus the reanalysis products contain significant uncertainty. However, despite these limitations, “a decline in AMOC over the last 60 years,” Terhaar concludes “seems very unlikely.”

Authors: Jens Terhaar1,2,3*, Linus Vogt1,4, Nicholas P. Foukal1,5

1 Woods Hole Oceanographic Institution, Woods Hole, MA, USA

2 Climate and Environmental Physics, Physics Institute, University of Bern, Bern, Switzerland

3 Oeschger Center for Climate Change Research, University of Bern, Switzerland

4 Laboratoire d’Océanographie et du Climat Expérimentations et Approches Numériques (LOCEAN), Sorbonne Université, CNRS/IRD/MNHN, Paris, France

5 Skidaway Institute of Oceanography, University of Georgia, Savannah, GA, USA

The Woods Hole Oceanographic Institution (WHOI) is a private, non-profit organization on Cape Cod, Massachusetts, dedicated to marine research, engineering, and higher education. Established in 1930, its primary mission is to understand the ocean and its interaction with the Earth as a whole, and to communicate an understanding of the ocean’s role in the changing global environment. WHOI’s pioneering discoveries stem from an ideal combination of science and engineering—one that has made it one of the most trusted and technically advanced leaders in basic and applied ocean research and exploration anywhere. WHOI is known for its multidisciplinary approach, superior ship operations, and unparalleled deep-sea robotics capabilities. We play a leading role in ocean observation and operate the most extensive suite of data-gathering platforms in the world. Top scientists, engineers, and students collaborate on more than 800 concurrent projects worldwide—both above and below the waves—pushing the boundaries of knowledge and possibility. For more information, please visit www.whoi.edu

die_fesche_lola on January 27th, 2025 at 21:17 UTC »

Oh man, this is really good news. Just a few months ago there were news AMOC was slowing down and could stop as early as 2035 (timeline of 2035-2100).It personally freaked me out. The majority of people does not understand the devastating impact of AMOC slowing down and stopping. We would be in deep deep trouble.

Thanks OP for sharing this one ❤️

AdmiralSaturyn on January 27th, 2025 at 20:42 UTC »

So the AMOC is not in as much danger as we thought? We have more time than we thought? This is fantastic and very important news if true. However, climate change deniers are going to smugly cite this study as an excuse to delay cleaner energy initiatives on top of downplaying the dangers of global warming.

ahothabeth on January 27th, 2025 at 20:34 UTC »

Great news if true; but that does not mean we should be complacent.