Phase Shift of AMOC and Multidecadal Global Mean Surface Temperature Under Anthropogenic Forcing

Under greenhouse gas forcing, the global climate exhibits a long-term warming trend superimposed with quasi-periodic multidecadal oscillations (~60–70 years) closely linked to the Atlantic Meridional Overturning Circulation (AMOC). As a pivotal component of global ocean circulation, the AMOC regulates the distribution of oceanic heat and freshwater, exerting profound influence on global climate variability. Conventional views posit a positive correlation between AMOC strength and global mean surface temperature (GMST) on multidecadal timescale. However, our analysis reveals a significant phase shift of approximately 45°–90° between AMOC and GMST on multidecadal timescale under anthropogenic warming. This shift arises as enhanced vertical ocean heat transport within the subpolar North Atlantic’s mid-depth layers modulates the surface energy budget balance under increasing radiative forcing, thereby disrupting the equilibrium between horizontal meridional heat transport and surface net heat flux. External radiative forcing perturbs internal climate variability, driving a substantial reduction in mean-state density in the subpolar North Atlantic’s mid-depth ocean. Crucially, the intensified vertical heat transport associated with AMOC strengthening emerges as the key mechanism facilitating heat sequestration into the ocean interior.