Terminating the 100 kyr ice age cycle

Abstract

We report a simulation of the most recent 100,000‐year glaciationdéglaciation cycle of the late Pleistocene ice age, a simulation that delivers an ice sheet chronology that is in close accord with that inferred from the geological record. Our analyses are performed with a reduced model of the climate system that incorporates significant improvements to the representation of both climate forcing and mass balance response in a previously described theory based upon a coupled one‐level energy balance model (EBM) and vertically integrated ice sheet model (ISM). The theory fully incorporates the influences of orbital insolation forcing, glacial isostatic adjustment and variations in the atmospheric concentrations of greenhouse gases. It correctly predicts the main geographical regions of the northern hemisphere that were glaciated at last glacial maximum 21,000 years ago as well as the abrupt termination of the glacial epoch that occurred subsequently. The latter feature of the ice age cycle is obtained without the need to incorporate unconstrained and therefore controversial physical processes into the model, a limitation of all previous attempts to understand this global scale climate cycle. Our analyses suggest that the radiative impact on surface glaciation due to the changing atmospheric concentration of CO2 Is critical to the ability of the model to deliver a synthetic history of glaciation and déglaciation that is in accord with inferences based upon surface geological and geomorphological evidence. With the incorporation of this influence, model‐predicted ice thickness distributions at last glacial maximum (LGM) are very similar to those of the recently described ICE‐4G reconstruction that was based upon the inversion of postglacial relative sea level histories.