The climate of the Last Glacial Maximum: Results from a coupled atmosphere-ocean general circulation model

Results from a coupled atmosphere-ocean general circulation model simulation of the Last Glacial Maximum reveal annual mean continental cooling between 4° and 7°C over tropical landmasses, up to 26° of cooling over the Laurentide ice sheet, and a global mean temperature depression of 4.3°C. The simulation incorporates glacial ice sheets, glacial land surface, reduced sea level, 21 ka orbital parameters, and decreased atmospheric CO₂. Glacial winds, in addition to exhibiting anticyclonic circulations over the ice sheets themselves, show a strong cyclonic circulation over the northwest Atlantic basin, enhanced easterly flow over the tropical Pacific, and enhanced westerly flow over the Indian Ocean. Changes in equatorial winds are congruous with a westward shift in tropical convection, which leaves the western Pacific much drier than today but the Indonesian archipelago much wetter. Global mean specific humidity in the glacial climate is 10% less than today. Stronger Pacific easterlies increase the tilt of the tropical thermocline, increase the speed of the Equatorial Undercurrent, and increase the westward extent of the cold tongue, thereby depressing glacial sea surface temperatures in the western tropical Pacific by ∼5°-6°C.