Changes in the Efficiency of Meridional Heat Transport as a Snowball Initiation Mechanism

Abstract

The geological record indicates that Earth experienced several global glaciations—so-called “snowball Earth” events—the most recent of which shortly preceded the emergence of complex life. These are usually attributed to a runaway ice-albedo feedback triggered by solar or atmospheric ${\text{CO}}_2$ radiative forcing crossing a critical threshold. In this study, we use the Budyko-Sellers energy-balance model to demonstrate that such events can also be initiated by changes in the efficiency of meridional heat transport, potentially driven by tidal resonances with the Sun or Moon or by continental reconfiguration. We identify two special points associated with this mechanism—the neutral point, where the heat transport efficiency does not affect the ice coverage, and the transcritical point, where the snowball transition occurs precisely at the neutral point. We find that these points correspond to special climate states characterized by maximal meridional heat transfer, entropy production, and sensitivity to perturbations. Moreover, we show that when the climate is marginally baroclinically stable, the transport efficiency is near the value that maximizes the rate of entropy production, so that any mechanism pushing the climate toward marginal baroclinic stability also pushes it toward a state of maximum entropy production. Finally, by partitioning the model into an ocean and an atmosphere, we show that destabilization into a snowball state can result either from increased atmospheric or decreased oceanic transport efficiency. Our findings suggest a novel mechanism for snowball initiation and the organization of global climate that should be further investigated with large-scale models and geological tests.