Numerical experiments on ice age climates

Numerical experiments with a hemispheric thermodynamic model are carried out, using present and ice age conditions. The computed surface temperatures for 18,000 years ago are in good agreement with the CLIMAP values. It is shown that the snow-ice cap that existed in the summer 18,000 years ago created a feedback mechanism which was responsible for perpetuating these ice age conditions. The increase of insolation due to orbital variations was responsible, at least in part, for the shrinkage of the snow-ice cap from 18,000 to 8,000 years ago. It is shown that the effect on the earth-atmosphere system of the changes in insolation due to the orbital variations depends on the preexisting snow-ice cap. It is significant for the ice cap that existed 18,000 years ago and insignificant for present conditions. The numerical experiments suggest that the evolution of climate depends in an important way on the initial snow-ice conditions. Therefore, according to the model the problem of simulating the evolution of climate is not determined if one does not prescribe these snow-ice conditions. Lamont Doherty Geological Observatory contribution No. 3115. Visiting Senior Research Associate at Lamont Doherty Geological Observatory, Columbia University.