A major ocean current system, crucial for regulating the climate across the Northern Hemisphere, is expected to weaken far more severely by the end of this century than previously estimated, according to a new study published in Scientific Progress.
The Atlantic Meridional Overturning Circulation (AMOC) is a vast ocean current system that transports warm water north from the tropics, releasing heat into the atmosphere, then sinking and returning south.
Dr. Valentin Portman, lead author from Bordeaux Southwest Research Center in France, explains, “This loop transports heat from the equator to the North Atlantic Ocean,” as reported by BBC Science Focus.
The warm, salty water moves north, releases heat, thickens, sinks, and subsequently flows south through deep ocean currents.
Research predicts a 51% slowdown of AMOC by 2100, approximately 60% higher than average projections from standard climate models and with considerably lower uncertainty.
The implications of a weakened AMOC could be dire. Sea levels along the Northeast Coast of the United States are already rising faster than the global average, partly due to AMOC’s decline.
Globally, the tropical rain belt is anticipated to weaken and shift south, endangering the monsoon systems vital for agriculture in West Africa and South Asia.
In Europe, these changes could result in colder, harsher winters as the warm water conveyor belt slows down.
Every further weakening brings the AMOC closer to a tipping point, increasing the chances of complete collapse with potentially catastrophic outcomes.
The Importance of AMOC
Predicting the future of AMOC as global temperatures rise is notoriously challenging. Its vast, complex nature is influenced by both local and global factors.
Previous assessments of AMOC’s future varied widely between climate models. While most agree on its weakening, estimates of its collapse range from minimal to catastrophic.
The latest study identified systematic errors in some of the best existing models: underestimating salinity in the South Atlantic and overestimating temperature in the North Atlantic.
These biases lead to an underestimation of the critical process that allows dense, saline water to sink, maintaining current flow within the system.
After correcting these discrepancies using ridge-normalized linear regression — a rarely applied technique in climate science — researchers found the expected weakening of AMOC increased to 51%, considerably lowering result uncertainty.
“Typically, models use one variable as input, like past AMOC strength,” Portman noted.
“Our goal was to utilize more comprehensive data by analyzing multiple variables concurrently, considering the complexity of AMOC.”
The current AMOC is already showing signs of weakness, as evidenced by observational data revealing a 10% to 20% intensity decline since the mid-2000s — equivalent to significant volumes of water no longer flowing north each second.
According to a 2025 study, recent AMOC weakening has contributed up to 50% of flooding along the U.S. Northeast coast since 2005.
However, researchers caution that linking this decline directly to anthropogenic climate change, rather than natural fluctuations, remains uncertain until at least 2033, when sufficient data will be available.
Understanding the Risks
While the findings of this study are concerning, researchers clarify what they do and don’t imply.
The 6th Assessment Report from the Intergovernmental Panel on Climate Change (IPCC) expressed confidence that AMOC will weaken throughout this century but reported “moderate confidence” that it would avoid total collapse by the year 2100.
However, these reassurances may offer little comfort given the impact of such a collapse, whether it occurs before or after 2100.
Moreover, a 2025 study published in Geophysical Research Letters indicated that under serious collapse scenarios, severe cold temperatures could drop to -20°C (-4°F) in London and -48°C (-54°F) in Oslo, despite global warming trends.
A weakening AMOC also raises the risk of breaching an unknown tipping point. According to a study, AMOC may exist in two stable states, and once reversed, it could take thousands of years to revert.
The exact location of this threshold is uncertain. A 2025 study in Environmental Research Letters revealed that under high emissions, AMOC shutdowns could occur in 67% of operations, and 30% under moderate emissions.
“The threshold remains elusive,” Portman stated, “but this accelerated decline we observe may be approaching a tipping point.”
Future Projections
Portman’s team assessed four different emissions scenarios, three of which (from moderate to very high) indicate similar 50% weakening results, suggesting that beyond a certain emissions level, many consequences of climate change become inevitable.
“We’ve introduced significant heat into the ocean, and its chilling effects will last for centuries,” Portman warned.
The most optimistic scenario, emphasizing strong and sustained emissions reductions, resulted in only a 20% weakening of AMOC.
“We can frame it two ways: it’s late, given our high CO2 emissions and their long-term impacts,” Portman said, “but we can also assert that significant reductions before reaching a tipping point can avert a serious decline.”
Currently, Portman believes his research offers a clearer view of the AMOC’s future, though he acknowledges ongoing uncertainties and the potential for additional undiscovered processes.
“That’s why it’s critical to approach these findings cautiously,” he emphasized. “Addressing uncertainty in climate models is essential for understanding AMOC’s fate.”
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Source: www.sciencefocus.com
