‘Countries need to prepare now’: Major Atlantic currents are much closer to collapse than scientists thought

The Atlantic currents, which are essential to keeping the Earth’s climate in check, may be halved in strength by 2100 and may be closer to collapse than originally thought, a new study has found.

The Atlantic Meridian Circulation (AMOC) acts as an oceanic conveyor belt, circulating warm water north from the tropics and cold water south. This regulates the climate across Europe, Africa, and America, while also preserving aquatic life.

One study now estimates that the AMOC will slow by between 43% and 59% by 2100, a 60% stronger slowdown than past models predicted. The study corrected biases in previous estimates by including Atlantic surface temperature and salinity, according to findings published Wednesday (April 15) in the journal Science Advances.

you may like

This “more significant weakening of the AMOC” means that important planetary systems are closer to a tipping point, or an irreversible climate “point of no return,” than many past models suggest, the authors say in their study.

But other experts point out that the predicted magnitude and speed of the AMOC slowdown varies widely from study to study.

“In my opinion, the new results of each study need to be interpreted in a broader context,” Maria Paz Chidicimo, an expert on ocean circulation at the National Council for Scientific and Technical Research (CONICET) and the National University of San Martín in Buenos Aires, Argentina, told Live Science via email.

He added: “Studies predict AMOC declines ranging from small to large declines, but given the high variability in model predictions, we think the magnitude and timing of AMOC declines are still uncertain.”

Laura Jackson, a North Atlantic current expert at the Met Office, agrees. “Which model’s AMOC predictions are most likely is still an open question,” she told Live Science via email.

catastrophic collapse

The collapse of AMOC will last hundreds to thousands of years and have catastrophic consequences. This will cause temperatures in northern Europe to plummet and southern Europe to experience extreme drought. Sea levels will rise along the northeast coast of North America. Disruptions will spread throughout food webs and ecosystems in the ocean and on land. For example, the amount of land available for growing wheat and corn, which provide two-fifths of the world’s calories, would be cut by more than half.

Modeling AMOC slowdown

Observations reveal that the AMOC has weakened compared to the 1850-1900 baseline. Previous studies have attempted to estimate the strength and pace of the AMOC’s slowdown, with some finding minimal decline by the end of the century and others predicting imminent collapse.

What to read next

However, since continuous monitoring of the AMOC only began in 2004, few previous studies have included real-world observations in their calculations. And when real data is used, most studies incorporate only a single observable variable, such as past AMOC strength or seasonal mean temperature changes, the authors say in their study.

However, because the AMOC is a complex system, climate models need to account for multiple observable variables, the authors write.

In this new study, researchers used a variety of statistical methods to compare the performance of different climate models that predict AMOC based on different emissions scenarios and assess which is most accurate at predicting future AMOC slowdowns.

Scientists found that the most accurate model combined sea surface temperature and salinity across the Atlantic Ocean, using statistical techniques rarely used in climate modeling. The method, called “ridge regularized linear regression,” reduced the model’s prediction error by 79% compared to standard modeling techniques.

The model estimates that AMOC will slow by about 51% from the 1850-1900 average. The Intergovernmental Panel on Climate Change (IPCC)’s 2022 report called the 50% slowdown in AMOC a “significant weakening.”

“This is an important result with implications for the future climate of the Atlantic Ocean and beyond,” the authors say in their study.

While these results are not particularly surprising, the finding that “the predicted weakening is greater than previously thought” is clearly concerning, David Thornalley, a professor of ocean and climate science at University College London in the UK who was not involved in the study, told Live Science via email.

The predicted AMOC is “so weak that it is very likely that it will go towards a complete shutdown,” Stephan Rahmstorf, a professor of ocean physics and head of the Earth System Analysis Division at Germany’s Potsdam Institute for Climate Impact Research, told Live Science in an email.

Still, experts told Live Science that the AMOC model’s estimates depend primarily on which variables are included in the analysis, so results may vary. And while the new study corrects for previous biases, “uncertainty remains about how well the models can simulate and predict changes in the AMOC,” Thornalley said.

Chidicimo said focusing too much on AMOC’s collapse may not be the most useful path forward. “There is sufficient scientific evidence of AMOC fluctuations and slowdowns, and we are already experiencing that environmental changes associated with AMOC changes are having important socio-economic impacts around the world,” he said. “Countries need to prepare now.”