Freshwater pouring from Greenland’s melting ice sheet significantly strengthens the weakening of the Atlantic Meridional Overturning Circulation (AMOC) in long-term climate simulations, yet a new study suggests the current does not suddenly collapse or become irreversible. Instead, the weakening remains gradual and recoverable, even under a very high emissions scenario extending to 2300.
The future of the Atlantic Meridional Overturning Circulation (AMOC) has become one of the biggest unresolved questions in climate science. Because the circulation transports warm surface water northward and returns colder, deeper water southward, it plays a central role in redistributing heat, supporting marine ecosystems, and helping maintain stable weather patterns.
Scientists have long expected the AMOC to weaken as the climate warms. What has remained uncertain is whether it could eventually reach a tipping point, where the system abruptly collapses and becomes difficult—or even impossible—to restore.
A new study published in Science Advances offers a fresh perspective by examining a factor that many standard AMOC climate models do not fully include: the growing flow of freshwater from Greenland’s melting ice sheet.
Greenland Meltwater Changes the Picture
Previous research has suggested that freshwater from Greenland can weaken the AMOC by making North Atlantic waters less salty and reducing the sinking of dense water that helps drive the circulation.
However, researchers say many standard AMOC-focused climate projections have not explicitly accounted for this increasing freshwater input. That raised an important question: Could Greenland’s melting ice be the missing ingredient that pushes the AMOC past a critical tipping point?
To investigate, the researchers incorporated Greenland meltwater into a state-of-the-art climate model.
They used the CMIP6-class EC-Earth3 climate model under a very high emissions scenario extending through 2300. To isolate Greenland’s influence, they ran paired simulations with and without additional meltwater entering the North Atlantic.
The comparison revealed that Greenland’s freshwater does indeed make a measurable difference—but not in the dramatic way some had feared.
The Current Weakens More, but Does Not Crash
The simulations showed that Greenland meltwater contributes substantially to additional AMOC weakening, particularly after 2100.
According to the researchers, the added freshwater causes about 1 sverdrup of additional weakening by 2100, representing roughly 10% of the weakening caused by rising carbon dioxide alone.
By 2300, that additional weakening grows to approximately 4 sverdrups, or nearly 40% of the CO₂-driven weakening under the study’s strongest emissions scenario.
Despite this considerable impact, the model never produced an abrupt shutdown of the circulation.
Instead, the AMOC weakened in a relatively smooth, nearly linear fashion as cumulative carbon dioxide emissions increased. The researchers found no evidence of the sudden jump typically associated with a classic climate tipping point.
Rather than switching off completely, the circulation remained active while becoming both weaker and shallower.
Why Greenland Freshwater Has Such a Strong Effect
The study also sheds light on the mechanism behind the additional weakening.
As more freshwater enters the North Atlantic, the model shows that the primary regions feeding the AMOC gradually shift farther north toward the Arctic.
There, freshwater-driven freshening increases ocean stratification, making surface waters less likely to mix with deeper layers. This reduced mixing weakens the processes that normally help sustain the overturning circulation.
The researchers suggest this shift in AMOC source regions explains why Greenland meltwater becomes increasingly important over time, especially after 2100.
Could a Severely Weakened AMOC Recover?
One of the most important questions surrounding climate tipping points is whether they are reversible.
To explore this, the research team conducted two additional experiments after 2250.
In one simulation, atmospheric carbon dioxide levels were gradually reduced. In the other, the additional Greenland meltwater was simply turned off while keeping other late-23rd-century conditions unchanged.
Both experiments pointed toward recovery rather than permanent change.
When the meltwater forcing was removed, the AMOC gradually strengthened over the following centuries. After 200 years, the meltwater-driven weakening at 40°N declined from −2.7 sverdrups to −0.7 sverdrups compared with the reference simulation.
The researchers concluded that the circulation appears capable of recovering on multi-centennial timescales and does not exhibit the kind of irreversible behavior typically associated with a true tipping point.
Likewise, the simulations in which carbon dioxide concentrations were reduced also showed the AMOC recovering, even after centuries of enhanced Greenland meltwater input.
The Debate Is Far From Settled
Although the findings provide encouraging evidence that Greenland meltwater alone may not trigger an abrupt AMOC collapse, the researchers emphasize that important uncertainties remain.
Climate scientists broadly agree that the AMOC is likely to weaken during this century. However, whether that weakening eventually reaches an abrupt tipping point continues to be actively debated.
Recent assessments by the Intergovernmental Panel on Climate Change (IPCC) found that current CMIP6 climate models do not simulate an abrupt AMOC collapse during the 21st century.
At the same time, other recent research has suggested that the Atlantic “cold blob” could indicate that the system is moving closer to a tipping threshold if future conditions worsen.
The authors of the new study caution that their conclusions come from only a single climate model. Different models may represent Greenland meltwater pathways differently or have varying levels of AMOC stability.
Because of that, they argue that similar experiments should be repeated across multiple climate models to determine whether the gradual and reversible behavior found in this study holds more broadly.
Why This Matters
The new findings suggest that Greenland ice melt is an important driver of future AMOC weakening and becomes increasingly influential after 2100. However, within this model, the additional freshwater does not trigger the abrupt, irreversible collapse that has been feared in some tipping-point scenarios.
That distinction matters because it changes how scientists think about future risks. A steadily weakening AMOC could still have significant consequences for climate, ocean circulation, and weather patterns, but the absence of a sudden shutdown in these simulations suggests the system may respond more gradually than some scenarios predict.
Even so, the researchers stress that this is not the final word. Testing these results across multiple climate models will be essential to determine whether this picture of a weaker—but persistent and recoverable—AMOC proves to be a robust feature of Earth’s future climate.
