An investigation of the astronomical theory of the ice ages using a simple climate-ice sheet model

Abstract

THE astronomical (or Milankovitch) theory of the Quaternary ice ages has been the subject of several recent studies using simple climate models^1–3; this approach is potentially more complete than earlier ‘insolation curve’ investigations⁴. The external forcing of this theory, that is, variations in incident sunlight due to secular earth orbit perturbations, is well known⁵, and deep-sea sediment core records^6,7 provide a good data base for testing the model results. If any component of this data can be linked conclusively to the astronomical forcing, this would provide useful knowledge of the sensitivity/stability of the present climate² (for example, to several types of human perturbations). This letter describes an attempt to incorporate the ice sheets explicitly into a simple climate model's description of the global weather, guided by the fact that ice sheet variations are the principal features of the ice ages, but with these variations forced mainly by relatively small changes in the weather. The results combine features of previous results of purely climatological^1,2 and purely glaciological models^3,8, with the ice sheets' albedo feedback, topography and dynamics all being important in the present model. The curve of the model's ice ages is similar to previous model curves^2,3, comparing favourably with some aspects of the deep-sea record but not simulating the dominant ∼ 100,000 yr ‘sawtooth’ cycle of this data at all.