Winter and Summer Climate Change in the Last Glacial Maximum Simulated by a Coupled Model

Abstract

Boundary conditions of the last glacial maximum (LGM) were implemented in an atmosphere-ocean-sea ice coupled model and a climate response in winter and summer is investigated. Whereas global mean surface air temperature (SAT) decreases in a similar magnitude in both December-January-February (DJF) and June-July August (JJA) by about 10.5℃ with LGM conditions, over land the surface cooling is larger in JJA (16.2℃) than in DJF (15.6℃). The larger SAT reduction in JJA is due to a larger snow-ice albedo feedback, especially over the Laurentide and Fennoscandian ice sheets and Asia. In association with the marked surface cooling, mean sea level pressure (MSLP) substantially increases in high latitudes such as the Laurentide, Fennoscandian, and Antarctic ice sheets in DJF, and over Asia in JJA, whereas MSLP is reduced in the subtropics. The MSLP increases over the Southern Ocean (SO) and the northern North Atlantic associated with an increase in sea ice extent, leading to a reduction in westerly winds, especially in the SO in both seasons. Associated with the change in MSLP, cloud cover tends to decrease in high latitudes and increase in subtropics, and this change is reflected in a change in precipitation fields. In high latitudes, precipitation is largely reduced in both seasons with a larger reduction in JJA, whereas in subtropical regions precipitation slightly increases. In regions of marked surface cooling such as the northern North Atlantic in DJF and over the Laurentide and Fennoscandian ice sheets and Asia in JJA, evaporation decreases substantially even more than precipitation reduction, leading to a wet climate. In conclusion, the climate response is larger in JJA than in DJF to the LGM conditions and this is associated with the larger snow-ice albedo.