Glacial-interglacial cycles are often described as an amplified global response of the climate to perturbations in solar radiation caused by oscillations of Earth’s orbit. However, it remains unclear whether internal feedbacks are large enough to account for the radically different glacial and interglacial states. Here I will first discuss a modeling study providing support for an alternative view: Glacial-interglacial states are multiple equilibria of the climate system that exist for the same external forcing. Multiple equilibria resembling glacial and interglacial states can be found in a complex coupled general circulation model of the ocean-atmosphere-sea ice system. The multiple states are sustained by ice-albedo feedback modified by ocean heat transport.
In the second part, I will explore the dynamics of Dansgaard–Oeschger events, specifically the processes controlling the Southern Hemisphere response to an abrupt warming event in the Northern hemisphere. Starting from the glacial state, an abrupt NH warming is forced via an eccentricity-related solar radiation perturbation. In connection with a reduction of the northward cross-equatorial ocean heat transport, a robust multi-decadal phasing between the two hemispheres, similar to the reconstructed one, emerges in the model. Factors influencing the phasing timescale will be discussed. Our results highlight the potential role of global coupled ocean-atmosphere processes, rather than the often-invoked Atlantic MOC, in controlling inter-hemispheric connections.