Structural stability changes of the Atlantic Meridional Overturning Circulation

The Atlantic Meridional Overturning Circulation (AMOC), a tipping climatic component, has a quasi-global impact and it could induce a cascade of critical transitions. There is considerable uncertainty regarding the location of the overturning circulation's current state relative to its stability thresholds. We identify similarities between observational and simulated spatial patterns, bifurcation diagrams and phase spaces linked with AMOC changes. The resemblances suggest that the overturning already underwent a Hopf bifurcation and entered a bistable regime before 1854, that it suffered a Rate-induced tipping around 1970, possibly linked with the Great Salinity Anomaly, and that it approached the attractor of its weak state. These changes in the overturning circulation dynamics are indicative of complex structural stability variations during the preindustrial revolution, which underline the need for a long-term temporal assessment of the overturning circulation stability on multi-centennial to millennial time-scales, to set its contemporary and future evolution in a long-term context.