A quasi-three-dimensional (3-D) climate model (Sellers, 1983) was used to simulate the climate of the
Last Glacial Maximum (LGM) in order to provide climatic input for the
modelling of the Northern Hemisphere ice sheets. The climate model is
basically a coarse-gridded general circulation (GCM) with simplified
dynamics, and was subject to appropriate boundary conditions for ice-sheet
elevation, atmospheric CO2 concentration and orbital parameters.
When compared with the present-daysimulation, the simulated climate at the
Last Glacial Maximum is characterized by a global annual cooling of 3.5°C
and a reduction in global annualprecipitation of 7.5%, which agrees well
with results from other, more complex GCMs. Also the patterns of temperature
change compare fairly with mostother GCM results, except for a smaller
cooling over the North Atlantic and the larger cooling predicted for the
summer rather than for the winter over Eurasia.
The climate model is able to simulate changes in Northern Hemisphere
tropospheric circulation, yielding enhanced westerlies in the vicinity of
the Laurentide and Eurasian ice sheets. However, the simulated precipitation
patterns are less convincing, and show a distinct mean precipitation
increase over the Laurentide ice sheet. Nevertheless, when using the
mean-monthly fields of LGM minus present-day anomalies of temperature and
precipitation rate to drive a three-dimensional thermomechanical ice-sheet
model, it was demonstrated that within realistic bounds of the ice-flow and
mass-balance parameters, veryreasonable reconstructions of the Last Glacial
Maximum ice sheets could be obtained.