A Song of Ice and Water: AMOC Stability amid Tipping Ice Sheets

Global warming is increasingly threatening the stability of the Earth system and may already have pushed it beyond critical thresholds known as tipping points. These arise from the climate system's nonlinearity, and when crossed, they can trigger self-reinforcing feedbacks leading to abrupt and potentially irreversible shifts. Tipping points are associated with subsystems called tipping elements, spanning all spheres of the climate system. Severe global consequences are linked to some of these, including the Atlantic Meridional Overturning Circulation (AMOC) and the Greenland and West Antarctic ice sheets (GIS, WAIS). Because these systems are interconnected, the tipping of one may trigger others in cascading tipping. For example, a GIS collapse would release meltwater capable of destabilizing the AMOC, which, if tipped, could warm the Southern Hemisphere and trigger WAIS collapse. Yet uncertainties remain, especially concerning whether WAIS meltwater acts to stabilize or weaken the AMOC. The key novel insight of this work is that, while a GIS tipping can strongly destabilize the AMOC, a WAIS tipping can counteract this effect. The stabilizing influence of WAIS meltwater on the AMOC, initially identified in conceptual models, is confirmed in the comprehensive model CLIMBER-X, providing robust evidence of its potential significance. The mechanisms behind this stabilization are elucidated, and the ice sheet tipping trajectories enabling it are shown to be particularly relevant under high greenhouse gas emissions scenarios. AMOC stability is further shown to depend not only on bifurcation-induced tipping, but also on rate- and noise-induced effects. Even for millennial-scale ice sheet tipping events, the rate of meltwater fluxes is found to be critical, with rapid changes capable of inducing additional instabilities. Natural variability in external drivers can likewise generate noise-induced transitions, but also reinforce WAIS-driven stabilization, highlighting that AMOC resilience depends not only on thresholds, but also on safe rates of change, and unresolved variability. At a theoretical level, the study advances the understanding of leading–following systems, the simplest framework for cascading tipping. Their analysis is extended to a broader class of nonlinear systems and interactions, and a new asymptotic approach is introduced to approximate their coupled bifurcation structures. This provides key insights into the dynamics of conceptual models and represents a first step toward a theoretical foundation for cascading tipping. Overall, these findings represent a significant advance in the understanding of interacting tipping elements, particularly the AMOC and polar ice sheets. The results demonstrate that stabilizing interactions, such as the influence of WAIS meltwater on the AMOC, may emerge as unintended consequences of a changing climate and must be considered in future projections. Accounting for these dynamics is essential to improve climate projections, inform mitigation strategies, and guide climate adaptation and planning.