Fig. 1. AMOC stability in modern climate and AMOC response under global warming.

(A) AMOC stability diagram where ${\mathit{M}}_{\text{ovS}}^{*}$ and ${\mathit{M}}_{\text{ov}}^{*}$ are the AMOC stability indicators defined in Materials and Methods. The indicator values in modern climate are shown in solid circles for reanalysis data [Centro Euro-Mediterraneo sui Cambiamenti Climatici Global Ocean Physical Reanalysis System (C-GLORS; pink), Estimating the Circulation and Climate of the Ocean version 4 (ECCO-v4; brown), Ocean Reanalysis System 4 (ORAS4; green), and Simple Ocean Data Assimilation (SODA; yellow)], in gray triangles for the CMIP5 model simulations, and in blue and red diamonds for the CCSM3 CTL and ADJ runs. A positive or negative $\mathrm{\Delta }{\mathit{M}}_{\text{ov}}^{*}$ indicates that the AMOC resides in a stable or unstable regime. (B) ${\mathit{M}}_{\text{ovS}}^{*}$, $\mathrm{\Delta }{\mathit{M}}_{\text{ovN}}^{*}$, and $\mathrm{\Delta }{\mathit{M}}_{\text{ov}}^{*}$ from reanalysis data, the CCSM3 CTL and ADJ runs with the same marker and color scheme as in (A), and the CMIP5 climate models in the form of the box-and-whisker plot. (C) Evolution of AMOC strength in the CTL (blue), CTLCO₂ (light blue), ADJ (red), and ADJCO₂ (orange), where the AMOC strength is defined as the maximum in the stream function below 500 m in the North Atlantic. A locally weighted scatterplot smoothing of 10-year intervals is applied to annual mean AMOC strength to remove interannual variability.