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Abstract

We present a 6-year simulation of the ice age atmosphere using the T21 Atmospheric General
Circulation Model (AGCM) of the European Centre for Medium-Range Weather Forecasts (ECMWF).
The lower boundary conditions (18 kyr B.P.) were taken from CLIMAP Project Members (1981). The
analysis is restricted to the surface climatology for two reasons: The surface fields are the test data
derived from the geological record on land, and they define the upper boundary conditions for
simulating the glacial ocean. Model results are shown for the mean annual surface fields of
temperature, wind, and precipitation. In the global average the surface temperature was 4.7øC cooler
compared to the present temperature. The wind strength increased in mid-latitudes and decreased in
tropical trade wind regions. Precipitation did not change significantly in the global average; however,
precipitation decreased over land and increased over the ocean. Most of the difference patterns
between the present conditions and the ice age climate were statistically significant. The simulated
surface climatology is roughly consistent with the paleogeological evidence and with numerical AGCM
simulations of other authors. This suggests that presently available AGCMs, including the ECMWF
model (T21), are able to describe climates far away from the present, although internal parameteriza-
tions were tuned to present data sets.