Collapse of the Atlantic meridional overturning circulation would lead to substantial oceanic carbon release and additional global warming

Abstract The potential collapse of the Atlantic Meridional Overturning Circulation could profoundly impact regional and global climates, yet its effects on the carbon cycle and subsequently global temperature remain seriously underexplored. Here we quantify carbon cycle responses across different background global warming levels using a fast Earth system model. We find that Atlantic Meridional Overturning Circulation collapse increases atmospheric carbon dioxide by 47–83 ppm carbon dioxide, leading to around 0.2 °C of additional global warming at higher carbon dioxide background levels after offsetting ocean-dynamics-driven cooling. Despite the modest global warming effect, regional temperature anomalies are pronounced: Arctic temperatures cool by ~ 7 °C (60 °N–90 °N), while Antarctic temperatures warm by ~ 6 °C (60 °S–90 °S). This latter response originates from deep convection triggered in the Southern Ocean, which ventilates deep carbon-rich waters. Such long-term equilibrium responses reveal key physical and carbon-cycle mechanisms and highlight substantial regional climate risks associated with an Atlantic Meridional Overturning Circulation collapse.