Abstract

Glacial-interglacial cycles (GIC) 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 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 addition, expansion/contraction of the Southern Hemisphere ice pack over regions of upwelling, regulating outgassing of CO2 to the atmosphere, is the primary mechanism behind a ~100pm CO2 change between the two states. If confirmed, a link between GICs and multiple stable states may provide an answer to puzzling aspects of the GIC , for example, why their amplitude is so regular despite the highly variable magnitude of insolation change during glacial terminations. In our perspective, the GIC ’s amplitude is primarily set by the separation between the multiple states (an intrinsic property of the unperturbed system) rather than by the forcing. The latter then provides the “kick” to trigger the transition from one state to the other.