Tipping interactions and cascades on multimillennial time scales in a model of reduced complexity

Abstract. A tipping cascade refers to a sequence of tipping events in the Earth system, where transitions in one subsystem can trigger subsequent transitions in other subsystems. These cascades represent a significant concern for the future, as the tipping of a single element could induce the tipping of interconnected elements that would not have otherwise crossed their thresholds. This chain reaction could lead to substantial and potentially irreversible changes in the Earth's system, even under low-emission scenarios. However, tipping cascades, particularly those involving ice sheets, may unfold over millennial timescales and are therefore rarely captured in state-of-the-art Earth system models, which typically run only until the end of the 21st century. In this study, we extend the simple climate model SURFER v3.0 to incorporate a network of interacting tipping elements and other nonlinear components. Using this extended model, we systematically investigate the occurrence of tipping events and cascades over multi-millennial timescales and under a range of realistic emission scenarios. We show that interactions among tipping elements generally increase their tipping risks, consistent with findings from previous studies. Furthermore, our results suggest that meeting the Paris Agreement target of limiting warming below 2 °C could lower the risk of observing tipping events and cascades by roughly an order of magnitude compared to current-policy pathways, underscoring the urgency of stronger climate action.