AMOC: Atlantic circulation could survive several centuries despite NADW shutdown

While scientists have long feared a rapid collapse of the Atlantic current, recent modeling indicates that the Atlantic Meridional Overturning Circulation (AMOC) could remain active for centuries even after North Atlantic Deep Water (NADW) formation disappears. This persistence, revealed by a study published in AGU Advances, challenges the most alarmist scenarios about future climate.

What the study reveals: precise results and key figures

The team led by Shantong Sun and Andrew Thompson compared the responses of different climate models to a gradual ocean warming. All models show that when NADW production drops, the cross-hemisphere water exchange does not disappear immediately. Instead, the exchange flow persists, even adjusts, for 'centuries', according to the most conservative simulations. This duration far exceeds previous predictions that anticipated a decisive weakening of AMOC by the end of the century. No model indicated a total shutdown of the overturning within the next 100 years, even under +4°C warming scenarios.

The authors emphasize that this persistence does not mean the system remains unchanged: transported volume decreases, heat is redistributed differently, and regional climate impacts on European and North American climates are attenuated but not eliminated. Thus, the study introduces a new nuance into the understanding of the climate tipping point threshold, distinguishing NADW loss from total AMOC disappearance.

Underlying scientific mechanisms

The simulations show that the meridional overturning relies on interconnected processes. When NADW formation, resulting from surface water cooling and salting in high northern Atlantic latitudes, weakens, other circulation pathways continue to feed interhemispheric exchange. Models indicate that surface currents, deep water upwelling from other basins (e.g., the Southern Ocean), and density exchange driven by salinity can maintain a 'backup circuit' for centuries. This dynamics explains why cross-hemisphere transport does not stop abruptly even if the main source (NADW) disappears.

Moreover, the hierarchy of models used in the study, combining classical general circulation models (GCMs) and high-resolution simulations enriched with machine learning, allowed capturing fine interactions between vertical convection, salinity mixing, and temperature variations. This hybrid approach has