“Severe consequences for Earth’s climate”: Scientists warn of food security impacts if AMOC collapses

27 Jul 2023 --- Scientists are warning that the Atlantic Meridional Overturning Circulation (AMOC), a part of the global conveyor belt moving water around the world, could collapse, severely impacting the climate in the North Atlantic region and globally. Other scientists have reacted to the study, saying it’s important not to ignore these findings while arguing a collapse in this century is unlikely. 

Nutrition Insight speaks with co-author Peter Ditlevsen, professor at the Niels Bohr Institute at the University of Copenhagen, Denmark, about the consequences of a collapse or changes in the AMOC.

How it might affect fisheries and ocean wildlife remains unknown, he says, while detailing food security’s impact from climate change. 

“On land, we’ll see a colder Western Europe, with consequences for farming and wildlife – compare farming in England with farming in Northern Canada and Alaska. Some models suggest that rain belts move, so we’ll have 40-50% less precipitation in the US Midwest and Mexico. This is very uncertain, though.”

“Shutting down the AMOC can have severe consequences for Earth’s climate, for example, by changing how heat and precipitation are distributed globally,” details Ditlevsen.

The weather changes would dramatically challenge all countries’ food production and water supply.Penny Holliday, head of marine physics and ocean circulation at the National Oceanography Centre and Principal Investigator for OSNAP (Overturning in the Subpolar North Atlantic Program), says that the strength of the out-of-sight ocean currents of the AMOC has surprisingly direct impacts on food, water and energy security, infrastructure risk, biodiversity and human health.

“The paper demonstrates that decades of observations are needed to detect a major tipping point in the AMOC, and the authors call for continued measurements of these great Atlantic ocean currents long enough to do so,” she adds. 

Threatens food system
Holliday details that the AMOC drives heat north through the Atlantic Ocean and sets the climate for all the continents on Earth. If the circulation was to collapse, lower surface temperatures and stronger winds through the whole northern hemisphere would occur after a few decades.

“Heat would pool in the Southern Ocean and South Atlantic, but over the southern continents, temperatures would decrease. Major rainfall zones would shift, leading to far less rainfall over Europe, North and Central America, North and Central Africa and Asia, and increased precipitation over the Amazon, Australia and southern Africa. Sea ice would extend southward from the Arctic into the subpolar North Atlantic, and the Antarctic sea ice would extend northward.”

These weather challenges would dramatically challenge all countries’ food production and water supply. Additionally, infrastructure would need significant investments to adapt to new weather, and energy supply and demand would change drastically. Moreover, it would increase diseases and negatively affect mental well-being, Holliday explains.

“Worldwide, many land and marine ecosystems would be unable to cope and adapt to such fast-changing climate conditions, and biodiversity would be severely impacted,” continues Holliday.

“While a cooling of Europe may seem less severe as the globe becomes warmer and heat waves occur more frequently, this shutdown will contribute to an increased warming of the tropics, where rising temperatures have already given rise to challenging living conditions.” 

“Most severely, the heat not transported to the North Atlantic stays in the tropics – on top of global warming. You may perhaps compare tropical Atlantic with tropical Pacific, where the hottest waters of any ocean are found in the warm pool near Indonesia – part of the El Nino system, which these days contribute to severe heat waves in North Africa and the Mediterranean,” explains Ditlevsen.

A study published last month showed that 90% of global aquaculture is at risk due to environmental change, detailing that many of the world’s largest aquatic food producers are highly vulnerable to human-induced environmental change, with some of the highest-risk countries in Asia, Latin America and Africa demonstrating the lowest capacity for adaptation.

Skepticism grows
Holliday says that the potential for the AMOC to collapse under global warming is a high-impact scenario but with low likelihood.

“International partners are investing in ongoing observations of the AMOC to determine how closely changes in AMOC contribute to changes in sea surface temperature and consequential climate and social and economic impacts on people,” she adds.

Dr. Jochem Marotzke, director of the Ocean Department in the Earth System at the Max-Planck-Institute for Meteorology in Hamburg, Germany, also comments on the study, “The statement so confidently made in this paper that collapse will occur in the 21st century has feet of clay.”

He argues that the math is solid, “but the starting point is highly dubious as the essential equation relies on the simplified models representing bifurcation – AMOC collapse – also being correct. But the more comprehensive models do not show this very bifurcation.”

“In this respect, the paper does not live up to its self-imposed claim: The strategy is to infer the evolution of the AMOC solely on observed changes in mean, variance and autocorrelation. The interpretation relies to an enormous extent on the authors’ theoretical understanding [of] being correct, and there are huge doubts about that,” adds Moritzke.Holliday says that the potential for the AMOC to collapse under global warming is a high-impact scenario but with low likelihood.

Dr. Johanna Baehr, Institute of Oceanography, University of Hamburg, Germany, shares the view of Marotzke.

“I am surprised that the authors derive such far-reaching conclusions regarding the future development of the AMOC from this purely mathematical analysis,” says Baehr. “In my view, the study’s results are not transferable to the actual future development of the AMOC. An abrupt collapse of the AMOC – as described in the 6th IPCC Assessment Report – is still not to be expected in the foreseeable future.”

Lack of long-term data
Experts have also pointed out that the AMOC has only been monitored since 2004, which makes long-term data unavailable and brings challenges of making precise estimations of when a collapse might occur.

Ditlevsen tells us: “Yes, that is true – unfortunately, we do not have direct monitoring of the AMOC dating back to the period before the climate change of industrial times.” 

“We have to rely on an indirect proxy, namely the sea surface temperature in the region of the deep water formation in the Atlantic. This fingerprint is not perfect, so there are uncertainties. We can monitor more in the future, but unfortunately, not in the past. This is the best we can do.”

“We need the past measurements to be able to distinguish the present observations of changes in the AMOC from the natural variability.” 

Nutrition Insight also spoke with Deepmala Mahla, vice president of humanitarian affairs at CARE, about climate change’s impact on malnutrition. 

“The climate crisis is a humanitarian crisis. We know that in several countries, the combination of conflict and climate-related events such as drought and flooding affects not only the communities’ ability to feed themselves and stay healthy, but also the market recovery and market development. We are seeing it increasingly, in more and more contexts.”

By Beatrice Wihlander