Simulated influence of carbon dioxide, orbital forcing and ice sheets on the climate of the Last Glacial Maximum

A coupled atmosphere–ocean–sea-ice model is used to investigate the climate of the Last Glacial Maximum (∼21,000 years ago) and the relative climate-forcing effects of atmosphere CO 2 , the Earth's orbital parameters and ice-sheet albedo. Tropical temperatures are found to be ∼2.2 °C less than today's—slightly colder than indicated by the CLIMAP palaeoclimate reconstruction. This result is consistent with a low to medium climate sensitivity to radiative perturbations. Temperatures are colder still in the northern North Atlantic region, owing to a weakening and shallowing of the thermohaline circulation. A sensitivity analysis suggests that changes in ocean circulation since the Last Glacial Maximum have not contributed directly to the global-mean temperature change since that time.