A significant ocean current system that plays a crucial role in regulating the climate across the Northern Hemisphere is projected to weaken more dramatically by the end of this century than previously anticipated, according to a new study published in Scientific Progress.
The Atlantic Meridional Overturning Circulation (AMOC) is an extensive ocean current system transporting warm water north from the tropics, releasing heat into the atmosphere before descending and returning south.
“This system essentially forms a loop that transports heat from the equator to the North Atlantic,” stated Dr. Valentin Portman, the lead author of the study from France’s Bordeaux Southwest Research Center, during an interview with BBC Science Focus.
“Warm, salty water flows north, releasing heat, thickening, sinking, and then traveling south through deep ocean currents.”
Research indicates a projected 51% slowdown by 2100, a figure approximately 60% higher than average projections derived from conventional climate models, with significantly lower uncertainty.
The weakening of AMOC could lead to severe consequences. Sea levels along the northeastern U.S. coast are already rising faster than the global average, partially due to a weakening AMOC.
Globally, the tropical rain belt is expected to weaken and shift southward, jeopardizing the monsoons on which millions in West Africa and South Asia depend for agriculture.
In Europe, these changes could result in harsher, colder winters as the conveyor belt of warm water to the continent decelerates.
Worryingly, each additional weakening increases the system’s proximity to a tipping point where complete collapse becomes more probable, posing potentially catastrophic risks.
Understanding a Complex System
Predicting the future of AMOC as the Earth warms is notoriously challenging due to the system’s vast complexity and influence from both local and global factors.
Previous forecasts about AMOC’s future varied significantly based on the employed climate prediction models. While most agree the system is weakening, the degree of potential collapse ranges from minimal to complete failure.
The new study identified two systematic errors prevalent in much of the prevailing modeling: underestimating salinity in the South Atlantic and overestimating coldness in the North Atlantic.
These biases cause models to underestimate how dense, saline water sinks and maintains current flow across the system.
By correcting these variables using a statistical approach called ridge-normalized linear regression, seldom applied in climate research, the expected weakening escalated to 51%, significantly lowering uncertainty surrounding the results.
“Typically, only one variable is used in studies, such as a singular observation of AMOC’s strength in the past,” Portman explained.
“This study aimed to incorporate more information by leveraging multiple variables simultaneously, which is vital due to AMOC’s complexity and dependence on various processes.”
The current strength of AMOC is already notably weak. Recent observations suggest a decline of 10% to 20% since the mid-2000s, equating to hundreds of millions of gallons of water no longer flowing north each second.
A 2025 study disclosed that the recent weakening of currents has contributed to nearly 50% of flooding along the northeastern U.S. coast since 2005.
However, attributing this decline to human-induced climate change rather than natural fluctuations remains a challenge. Experts state that it may take until 2033 (with 29 years of data) to confidently distinguish between the two.
Not a Complete Collapse—But It’s Worrisome
Results from this recent study are concerning, but researchers emphasize clarity regarding what they do and do not illustrate. In the 6th assessment report, the Intergovernmental Panel on Climate Change (IPCC) expressed confidence that AMOC would diminish throughout this century, albeit with “moderate confidence” that it would not collapse by 2100.
Yet, such assurances may offer little comfort given the extensive changes that collapse could entail, whether prior to or following this century’s conclusion.
For instance, a 2025 study in Geophysical Research Letters predicted that under such circumstances, temperatures in London could plummet to -20°C (-4°F) and -48°C (-54°F) in Oslo, despite global warming driven by greenhouse gases.
Moreover, a weakening AMOC risks crossing an unknown tipping point threshold. A study suggests that the AMOC may hold two stable “on” or “off” states, with reversals potentially taking thousands of years to rectify.
The exact location of this threshold remains uncertain. Extending existing models beyond the typical 2100 cutoff, a 2025 study in Environmental Research Letters indicated AMOC shutdowns could occur in 67% of high-emission scenarios and 30% under moderate conditions.
“We don’t definitively know where the threshold lies or if this situation truly applies,” Portman noted. “We can speculate that this decline, even more significant than predicted, may be approaching a tipping point.”
Critical Action Window
Portman’s team tested four distinct emissions scenarios. Three (ranging from moderate to very high) consistently yielded results of approximately 50% weakening, suggesting that many impacts of human-induced climate change could become irreversible beyond a certain threshold.
“We are introducing considerable heat into the ocean, which will persist for centuries,” Portman stated.
However, the most optimistic scenario, marked by robust and sustained emissions reductions, resulted in only about a 20% decline.
“There are two perspectives here. One is that it may be a bit too late, given significant CO2 emissions leading to long-term effects,” Portman explained.
“Conversely, if we dramatically lower CO2 emissions prior to hitting the tipping point, we can avert a serious decline.”
While Portman expresses confidence in his research’s projections for this important ocean system, he acknowledges that other significant processes may still need to be considered.
“This necessitates prudence regarding the findings,” he emphasized. “Substantial uncertainty remains in climate models concerning AMOC’s future. Addressing this issue is vital.”
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Source: www.sciencefocus.com
