Understanding glacial cycles: A multivariate disequilibrium approach

Abstract:

We find a consistent relation between orbital geometry and components of the climate system by returning to Milankovitch’s original hypotheses and focusing on the well-established physical concepts of an equilibrium state, disequilibrium from that state, and adjustment towards equilibrium. These mechanisms imply that the state of the climate system at any time depends on; (1) the state of the climate system in the previous period, (2) the degree to which this previous state is out-of-equilibrium with orbital geometry, and (3) the rate at which the climate system adjusts towards equilibrium. We evaluate this explanation by running experiments with a statistical model of climate that explicitly represents equilibria among variables and their movements towards equilibrium. Results indicate that; (1) skipped obliquity/precession beats are an artifact of ignoring adjustments towards an equilibrium state, (2) accounting for equilibrium and adjustments to equilibrium can account for all phases of the glacial cycle, and (3) glacial cycles are generated by adjustments to equilibrium relations between orbital geometry and climate and among components of the climate system. Together, these results suggest a new approach to understanding glacial cycles that is based on models which include a rich set of equilibria and adjustments to equilibria for a full suite of climate variables simulated over long periods.