Human-driven carbon emissions contributing to global warming are demonstrably slowing the Atlantic Meridional Overturning Circulation (AMOC). This crucial system of ocean currents, which includes the Gulf Stream, plays a significant role in moderating temperatures in Europe. A complete collapse of the AMOC could lead to a substantial release of carbon stored in the deep Southern Ocean back into the atmosphere. This phenomenon would act as a feedback loop, further exacerbating global temperature increases.
Previous research indicated that an AMOC shutdown might precipitate colder European winters, disrupt African and Asian monsoons, and contribute to rising global temperatures. However, recent advanced computer modeling has revealed an additional, concerning consequence: the potential emission of as much as 640 billion tonnes of carbon dioxide in the vicinity of Antarctica. This release could elevate global temperatures by an additional 0.2°C.
Da Nian, lead author of the study from the Potsdam Institute for Climate Impact Research in Germany, explained the mechanism. “AMOC collapse could trigger (in the) Southern Ocean big mixing and release the carbon stored in the deep water,” Nian stated. “It’s a quite new result.”
Johan Rockström, a co-author also affiliated with the Potsdam Institute, emphasized the broader implications. “The key message is that a very bad occurrence… could have even worse implications than we previously thought,” he remarked. “We have to be very careful, because when one thing goes wrong, it can have these domino effects.”
Understanding the AMOC’s Mechanism and Vulnerability
The AMOC’s operation is driven by variations in water density. It transports warm, saline water from the Gulf of Mexico towards the northern Atlantic. Upon reaching these cooler latitudes, the water cools, becomes denser, and sinks, initiating a southward return flow along the ocean floor. Scientists posit that freshwater runoff from the Greenland ice sheet is currently diluting this oceanic brine, thereby impeding the sinking process critical to the circulation’s integrity.
Recent measurements from buoys have confirmed a weakening of this southward return flow. The AMOC’s strength has already reportedly diminished by approximately 15 percent. Projections from climate models suggest that a complete collapse could occur at some point between decades and centuries from the present.
New Modeling Insights on AMOC Collapse and Climate Scenarios
The newly published study incorporated AMOC collapse scenarios across various future climate conditions. A significant finding was that when atmospheric CO2 concentrations reach or exceed 350 parts per million, the AMOC shows no signs of recovery following a shutdown. Given that current CO2 levels stand at 430 ppm, this suggests that any future AMOC collapse would likely be an irreversible event.
Furthermore, the research highlighted that a shutdown of the AMOC, which is intrinsically linked to the global oceanic “conveyor belt” extending into the Southern and Pacific Oceans, would instigate a reversal of deep water circulation near Antarctica. This deep water, largely isolated beneath a less saline surface layer, contains significant carbon accumulation derived from atmospheric absorption and the decomposition of marine organisms. The model indicates that a substantial portion of this sequestered carbon would then be released into the atmosphere.
Historical Precedents and Uncertainties in Southern Ocean Convection
Existing research into past AMOC collapses offers an explanation for the prospective onset of convection near Antarctica. It suggests that a reduction in salinity and sinking water originating from the northern Atlantic, flowing towards the Southern Ocean, would lead to a corresponding decrease in ocean salinity in Antarctic waters. This change would disrupt the stratification of less saline surface water over denser, saltier deep water, facilitating the upward movement of deep ocean currents to the surface.
Jonathan Baker of the UK Met Office commented on the study’s findings. “Seeing it play out in a warmer climate like this, and with such a large CO2 increase, is quite striking,” Baker noted. “It’s an interesting study, but it hinges on whether Southern Ocean convection strengthens, and that’s still quite uncertain, with different models showing different responses.”
Cascading Climate Impacts Beyond Carbon Release
Beyond the atmospheric carbon release, the study projected significant regional temperature shifts. An AMOC collapse is predicted to cause a 7°C cooling in the Arctic, leading to extreme cold in Canada, Scandinavia, and Russia. Concurrently, Antarctica could experience a 6°C warming. While the West Antarctic Ice Sheet already faces the risk of a tipping point, this intensified warming could potentially destabilize the considerably larger East Antarctic Ice Sheet, leading to a substantial rise in global sea levels.
Rockström cautioned that while the repercussions of the carbon release might unfold over millennia, humanity’s greenhouse gas emissions could potentially predetermine an AMOC collapse within the next few decades. “That commitment time may be… within the next 25 to 50 years. It’s literally now,” he stated. “What matters is not the impact time, it is the commitment time, because what right do we have to hand over to all future generations a less and less liveable planet?”
Journal reference: Nature Communications Earth & Environment DOI: 10.1038/s43247-026-03427-w