A collapse of the Atlantic Meridional Overturning Circulation (AMOC), the vast network of ocean currents that includes the Gulf Stream, could trigger a sharp drop in global food production and push food prices up by as much as 40 per cent, according to a new study by the Alliance to Feed the Earth in Disasters (ALLFED).
The study found that some countries could see their wheat, maize and rice production fall by nearly a fifth if the current collapses, with the resulting shortages capable of driving food prices sharply higher around the world.
"The ultimate price impact of an AMOC collapse will depend heavily on the ability of global agricultural supply and demand to adapt to the altered yield environment," the researchers said. "If the biophysical shock were to outpace adaptation, the economic impacts could be severe, driving a short-term global price spike of up to 40 per cent above baseline levels."
How the researchers modelled a collapse
For the study, which has not yet been peer reviewed, the ALLFED team used a computer model to simulate the AMOC's decline over the next 100 years under 2°C of warming above pre-industrial temperatures. One simulation also included an AMOC slowdown over the first 50 years, allowing the researchers to compare a world with and without the collapse.
The analysis showed that an AMOC slowdown would trigger overall cooling across the Northern Hemisphere, along with a southward shift in the belt of clouds and rain near the equator. By the 50-year mark, global yields of the most widely grown varieties of wheat, maize and rice had fallen by 5.3 per cent.
Some countries far worse hit than others
The impact was not spread evenly. Germany and Ukraine lost up to 19 per cent of their yields because of sudden, sharp cooling, while Canada saw a 12 per cent decline in production for the same reason.
"Scandinavia, the United Kingdom and Canada are particularly exposed," Michael Hinge, senior economist at ALLFED, told Live Science.
Building on earlier Exeter research
The findings build on earlier research led by Paul Ritchie, a climate scientist at the University of Exeter. His study found that in an AMOC collapse scenario, average British temperatures would fall by about 3.4°C by 2080, relative to a scenario without a collapse.
Rainfall during the April to September growing season would fall by about 123mm, and the area of Great Britain suitable for arable farming would shrink from about 32 per cent to just 7 per cent, according to that research.
Relocating farms is not simple
The ALLFED researchers said countries would need to prepare for major changes in where food is grown, with crops potentially having to move into regions where the new climate becomes more suitable. But relocating agriculture is far from straightforward, requiring land, water, infrastructure and investment, and the areas gaining suitable conditions may not have the capacity to take over production.
The scientists also warned that countries cannot simply look after their own food supplies. Maintaining international trade would be crucial, they said, because restricting exports when harvests fall could amplify shortages elsewhere. Countries would need to coordinate rather than retreat behind protectionist policies, otherwise a fall in production in one part of the world could rapidly become a global food crisis.
The team said they hope their work can help governments understand the need for swift, effective action if a collapse were to occur. Hinge warned that currently, "if that warning light starts flashing, we're not sure what to do with it." "There are no easy answers here, an AMOC [collapse] would be deeply catastrophic," he added.
Signs the current is already weakening
Studies have shown that the AMOC has already slowed by about 15 per cent since the mid-20th century because of climate change, and scientists say there is an almost one-in-four chance, between 10 and 24 per cent, that a catastrophic collapse is already locked in, according to a separate study.
Researchers have pointed to several warning signs that the AMOC could be heading for collapse:
- The current's strength has weakened by five per cent over 10 years
- The Gulf Stream has shifted north around North Carolina
- The amount of water transported by the Gulf Stream is reducing
- More northern areas of the ocean are experiencing warmer temperatures
- Ocean warming is focused on the western edge of the continental United States
Why the Atlantic current matters
The circulation of the Atlantic Ocean plays a key role in regulating global climate. A constantly moving system of deep-water circulation, often called the Global Ocean Conveyor Belt, carries warm, salty Gulf Stream water to the North Atlantic, where it releases heat into the atmosphere and warms Western Europe. The cooler water then sinks to great depths and travels to Antarctica before eventually circulating back to the Gulf Stream, a journey fuelled by differences in temperature and salt known as thermohaline currents. A complete circuit takes thousands of years.
Researchers believe that as the North Atlantic began to warm near the end of the Little Ice Age, meltwater from Arctic sea ice, ice sheets and glaciers gushed into the North Atlantic, diluting the surface seawater and making it lighter and less able to sink, which slowed the AMOC. The system has been weakening more rapidly since 1950 in response to recent global warming, researchers have found.
