An investigation of snowline instability in a coupled climate model: Implications for the Proterozoic

Abstract

An idealized geometry coupled climate system model is utilized to study the influence of the ice-albedo feedback on climate due to a gradual reduction in radiative forcing. Model results indicate a hysteresis behaviour in which multiple steady states can exist for the same values of solar luminosity. In one of the model experiments, millenial timescale variability is found and linked to a flush-collapse mechanism involving deepwater production in the northern hemisphere. Results suggest that previous model studies without coupled ocean components (eg. fixed sea surface temperatures, slab oceans with prescribed basal heat fluxes) may overestimate the climatic response to a radiative perturbation. The present experiments suggest radiative reductions appropriate to the Archean (17% reduced luminosity) as opposed to the Proterozoic (6% reduction) are necessary to facilitate a glaciated planet. Once initiated, a 1-2% increase in radiative forcing is capable of opening tropical waters. Sensitivity of the climate system model to the specified ice-albedo was also tested by considering a series of experiments in which the albedo effect was doubled that of the control. Global glaciation can then be achieved with an 11% reduction in radiative forcing. Unlike the control experiments, a 9% increase in radiative forcing is then required to exit global glaciation, upon exit the ice line retreats to subpolar latitudes (60 N) as opposed to tropical latitudes.