A coupled atmosphere-ocean-sea-ice model is used to investigate the climate of the Last Glacial Maximum (similar to 21,000 years ago) and the relative climate-forcing effects of atmosphere CO2, the Earth＇s orbital parameters and Ice-sheet albedo. Tropical temperatures are found to be similar to 2.2 degrees 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.