Deep in the Atlantic, an oceanic system pulsates, acting as the planet's thermostat. We're talking about the Atlantic Meridional Overturning Circulation (AMOC) , the great Atlantic current that distributes heat from the tropics northward and returns cold water at depth.
New research published in Environmental Research Letters warns that if emissions remain high, the AMOC could stall after 2100 ; even with intermediate or low scenarios, significant risks appear in several models, with profound effects in Europe and tropical rain belts.
How it works and where the balance is broken
With global warming, the ocean loses less heat in winter and the input of fresh water increases, so the surface remains warmer and lighter: it takes more effort for that water to sink and the mechanism weakens.
This loss of thrust activates a feedback loop: less salt water arrives from the south, the surface of the North Atlantic becomes less saline, the density decreases even further , and vertical mixing is slowed down even more.
The authors identify a tipping point when the deep winter mixing collapses; from there, the process self-amplifies and AMOC disruption becomes inevitable in the simulations.
What long-term simulations show
The work extends CMIP6 project reference models to the years 2300–2500, beyond the usual horizon. In all high-emission scenarios , deep overturn slows dramatically around 2100 and stops thereafter, transforming the circulation into a weak, shallow system.
Even with intermediate or low emissions, several models project this outcome: around 70% of the simulations collapse with increasing emissions, 37% with medium levels and 25% in the lowest scenario analyzed.
After the tipping point, the currents disappear completely between 50 and 100 years later , according to the models. The thermal energy that the North Atlantic delivers to the atmosphere would fall to less than 20%, and even close to zero in some cases.
This pattern represents a regime change rather than an instantaneous collapse: the AMOC loses its "deep engine" and becomes dominated by the wind-driven surface circulation.
Signals on the ground and what is missing from the models
Observation networks in the North Atlantic already point to a downward trend over the last decade, consistent with model projections. In the 26,5°N region, measurements indicate a weakening of approximately 0,8 Sv per decade , although the data series is too short for absolute certainty.
Researchers warn of structural limitations: some models are too stable and, in their standard version, do not adequately incorporate the freshwater input from Greenland's melting ice, which could underestimate the real risk.
Previous IPCC reports considered a collapse before 2100 unlikely; with the new long-horizon approach, that confidence weakens and risk management takes center stage.
Probable impacts in Europe and the tropics
For Western Europe, the implications include colder and more extreme winters and drier summers, as heat transport from low latitudes is reduced and storm tracks are altered.
Tropical rain belts would tend to shift, affecting regions dependent on that regime for agriculture, compromising food security in vulnerable areas.
The North Atlantic would absorb less heat and CO2, accelerating global warming due to reduced ocean uptake, and would decrease the supply of oxygen and nutrients, affecting ecosystems and fisheries in the Northeast Atlantic.
On the Atlantic coast of North America and other coastlines, the process could add about 50 centimeters to sea level , and alter storm patterns with impacts on infrastructure.
Overall, this paints a picture of Europe cooling regionally due to less heat transport, while other areas continue to warm, amplifying contrasts and the variability of the system.
Risk Management: Why the Next Decades Matter
The ocean's reaction time is long: avoiding a collapse before 2100 does not guarantee stability in the following century if a threshold has already been crossed.
Rapidly reducing emissions does not eliminate the risk entirely, but it significantly reduces it and delays the approach to the point of no return, gaining room for adaptation and monitoring.
Strengthening observations in key areas of the North Atlantic and improving models that better incorporate freshwater input are essential to refining timelines and risks.
What is clear and what is still under investigation
The emerging consensus is that the AMOC is weakening and that the risk of crossing a tipping point in the coming decades is real, with a transition to a weaker and shallower state if the emissions trajectory does not change.
Uncertainties remain about the exact timing and regional magnitude of the impacts, but the risk signal grows when the calculation horizon is broadened and the identified feedback mechanisms are considered.
New simulations and recent observations converge on a cautious but firm message: the great Atlantic current is under pressure , and the decisions of this generation will influence whether the system maintains its pulse or drifts towards a more fragile regime for centuries.
