Weakening Atlantic Ocean currents could cripple agriculture in some of the world's major breadbaskets, threatening global food security and raising the price of basic commodities, new research finds.

The study, which hasn't been peer-reviewed yet, investigated how a roughly 60% decline in the Atlantic Meridional Overturning Circulation (AMOC) would impact global food production. The AMOC is a system of ocean currents that regulates the global climate and brings heat from the tropics to the Northern Hemisphere.

However, the system is currently the weakest it's been in more than 1,000 years, having lost 10% to 20% of its strength due to climate change, estimates show.

In the new study, researchers used a computer model to simulate the AMOC's future decline. They modeled 100 years of change, assuming 3.6 degrees Fahrenheit (2 degrees Celsius) of warming above preindustrial levels. The team forced an AMOC slowdown over the first 50 years in one simulation but didn't modify the circulation in a second experiment, which enabled them to compare the world with and without an AMOC failure.

The model's outcomes mirrored the results of previous studies, showing broad cooling in the Northern Hemisphere and a southward shift of the belt of clouds and rain that encircles the globe near the equator. As in past studies, these effects were irreversible on human timescales, said study co-author Michael Hinge, a senior economist at the nonprofit Alliance to Feed the Earth in Disasters (ALLFED).

"Once the damage is inflicted, it stays there," Hinge told Live Science, adding that in the 50 years after the peak rate of AMOC slowdown in the model, the circulation weakened by an extra 20%. The study was posted on ALLFED's website July 7.

An agricultural "shock"

Hinge and his colleagues ran three models to look at the most common varieties of wheat, maize and rice, layering these models on top of the AMOC simulations. They found that global yields for these crops decreased by 5.3% by the 50-year mark, once the AMOC had weakened substantially.

"Lots of these effects manifest earlier, so it's a moving target," Hinge said.

He added that the results were based on a single warming scenario that was run once and used monthly rather than daily data, so they should be interpreted as a proof of concept. "We've set up a pipeline that is ready to take pretty much any AMOC scenario that can generate high-resolution climate data and see what it implies for crops," Hinge said.

While there was a 5.3% decrease overall, that global metric concealed huge differences between regions. For example, countries like Germany and Ukraine lost up to 19% of their cereal yields due to sudden, sharp cooling, while Canada showed a 12% decline in production for the same reason.

"Scandinavia, the United Kingdom and Canada are particularly exposed," Hinge said, "but there are many other [vulnerable] locations, some of which may be surprising even to the people who are living there."

For instance, the model produced a "very nasty brown splodge" of reduced precipitation over India, Pakistan and big parts of China, he said. Iran, Sudan and Eritrea, which are already water-stressed countries, also exhibited severe declines in rainfall, indicating that a portion of the agriculture there may not survive an AMOC collapse.

The 5.3% result also hides variability among years, Hinge said, because it's an average. So there may be years when global cereal losses reach 10% or more, which would bump up food prices, in part because countries might stockpile crops instead of trading them.

Global response

The regional effects of an AMOC slowdown would interact with climate change, triggering unpredictable outcomes. In particular, maladaptation — taking actions that end up backfiring — is a worry, Hinge said.

"You're preparing and setting up for much hotter temperatures or trying to develop areas for these temperatures and the trends you're seeing, and suddenly you see something different," he said. "That may cause an even larger compounding effect [on agriculture]."

The findings build on prior research led by Paul Ritchie, a climate scientist at the University of Exeter in the U.K., whose team explored the effects of an AMOC collapse on agriculture in Great Britain. That study, published in 2020, had similar limitations as the new one, so it's best to interpret both papers as a suggestion of what might happen rather than a precise forecast, Ritchie told Live Science in an email.

"I think the new study is valuable in showing the potential scale and geographic distribution of the initial agricultural shock," said Ritchie, who was not involved in the latest work. "What that would ultimately mean for food production and food security is more uncertain, because there are many possible responses by farmers, markets and governments." For that reason, the regional predictions may be more informative than the 5.3% global average, he said.

Average food prices worldwide could rise by 17% to 40% if the AMOC weakens to the extent it did in the model, the study predicts. The level of increase depends on how countries respond to the shock and their degree of preparedness, as well as on whether agriculture can be sustainably expanded in places like the African Sahel (the semi-arid zone directly south of the Sahara Desert) and Brazil, the analysis suggests.

The U.S. would not be spared from this price jump, and the model indicated that the country could see crop losses of about 3% for domestic wheat and corn. This loss would likely impact other foods that rely on cereal inputs, like meat, Hinge said. "The variety of foods available in the stores may well diminish for periods," he added.

An AMOC collapse would fundamentally deepen the need for countries to trade with each other, because some regions — such as the Indian subcontinent, China, Iran, Russia, Ukraine and Canada — could endure this giant shift only if they imported more food, Hinge said.

"Should countries turn inwards and start to restrict exports in an effort to ensure access for their own citizens first, or deal with the uncertainty, or offset concerns, then this will massively magnify the effects of AMOC," he said.

If governments behave as they have during past shocks, such as the 2008 financial crisis and the COVID-19 pandemic, they may restrict trade and start stockpiling food if and when the effects of AMOC weakening begin to show, Hinge predicted. The researchers hope their work and future modeling can help people understand the need to take swift, effective action if a collapse were to occur, he said.

Currently, "if that warning light starts flashing, we're not sure what to do with it," Hinge said. "There are no easy answers here; an AMOC [collapse] would be deeply catastrophic."