Polar glaciation and the genesis of ice ages

Abstract

One of the outstanding, unresolved climatic questions concerns the cause(s) of ice ages over geological time^1,2. A recurring theme in many hypotheses^2–4 has been that land at high latitude is a necessary condition, as snow accumulation on such land would accentuate local cooling via its albedo effect. Although the validity of these hypotheses has been queried⁵, they have been applied to the three most recent glacial periods, namely, the Quaternary (present), the Permo-Carboniferous (≃300 × 10⁶ years ago) and the Ordovician (≃450 × 10⁶ years ago). The involvement of high-latitude land has now been investigated with a general circulation model of the atmosphere, and the results presented here indicate that sea ice is readily produced in the model at high latitudes regardless of the existence of land. While land, or at least very shallow seas, may be necessary to promote glaciation, it appears that polar glaciation is the norm rather than the exception for the Earth. Thus no particular perturbation to the climatic system may be necessary to explain ice ages; rather the problem may be one of accounting for the intervening periods of warmth. The most promising solution to the latter problem is very large increases in the atmospheric CO₂ content.