Generalized stability landscape of the Atlantic Meridional Overturning Circulation

• Main Authors: Willeit, Matteo, Ganopolski, Andrey
• Format: Text
• Language: English
• Published: 2024
• Subjects: Arctic; Global warming; Nordic Seas; North Atlantic
• Online Access: https://doi.org/10.5194/egusphere-2024-1482; https://egusphere.copernicus.org/preprints/2024/egusphere-2024-1482/

The Atlantic Meridional Overturning Circulation (AMOC) plays a crucial role in shaping climate conditions over the North Atlantic region and beyond and its future stability is a matter of concern. While the stability of the AMOC to surface freshwater forcing (FWF) has been investigated in numerous model simulations, its equilibrium response to changing CO 2 remains largely unexplored and precludes a comprehensive understanding of AMOC stability under ongoing global warming. Here we use a fast Earth system model to explore the stability of the AMOC to combined changes in FWF between -0.25 and +0.25 Sv in the North Atlantic and atmospheric CO 2 concentrations between 180 and 560 ppm. We find four different AMOC states associated with qualitatively different convection patterns in the North Atlantic. Apart from an Off AMOC state and a Modern -like AMOC with deep water forming in the Labrador and Nordic Seas, we find a Weak AMOC state with convection occurring south of 55° N and a Strong AMOC state characterized by deep water formation extending into the Arctic. Several of these AMOC states can be stable under the same boundary conditions for specific combinations of CO 2 and FWF. Generally the model shows an increase in equilibrium AMOC strength for higher CO 2 levels. It is also noteworthy that, while under preindustrial conditions the AMOC off state is not stable in the model, it becomes stable for CO 2 concentrations above ~400 ppm, suggesting that an AMOC shutdown in a warmer climate might be irreversible.