Response of an ocean-atmosphere climate model to Milankovic forcing

Abstract. There is considerable evidence in support of Milankovic's theory that variations in high-latitude summer insolation caused by Earth orbital variations are the cause of the Pleistocene ice cycles. The enigmatic discrepancy between the spectra of Milankovic forcing and of Pleistocene climate variations is believed to be resolved by the slow, nonlinear response of ice sheets to changes in solar seasonality. An experiment with a preliminary version of a 14-region atmosphere/snow/upper ocean climate model demonstrates that the response of the ocean-atmosphere system alone to Milankovic forcing is capable of driving ice cycles with the observed spectrum. This occurs because of the highly nonlinear response of both the thermal seasons and the annual mean temperature to solar seasons, which is caused in turn by the highly nonlinear feedback between temperature and snow and sea ice.