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Schlagwörter:
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Zusammenfassung:
The atmospheric response to a hypothetical Tibetan ice sheet was tested with the T21 Atmospheric General
Circulation Model (AGCM) of the European Centre for Medium-Range Weather Forecasts (ECMWF). The
model response is discussed in terms ofan “autocycle" hypothesis of the ice ages proposed by Kuhle. According
to this hypothesis, ice-albedo feedbacks associated with the growth and retreat of the Tibetan ice sheet are the
mechanism that amplifies the variation of solar insolation on astronomical time scales, producing conditions
that favor glaciation or deglaciation in North America and Eurasia.
The imposed Tibetan ice sheet forcing did not increase the annual snow balance at the locations of the
Laurentide and Eurasian ice sheets. Analysis of the seasonal cycle results indicated that there were small areas
oflocally significant temperature decreases in July (at the ice sheet locations), but no corresponding precipitation
increases in January. The upper-tropospheric response to the elevated Tibetan plateau is not confined to the
vicinity of the forcing, but changes in the global energetics ofthe atmosphere are small (less than 5%) relative
to the control.
The results ofthis experiment do not permit a conclusive decision regarding the validity of Kuhle’s autocycle
hypothesis. Future modeling studies need to consider ocean-atmosphere—ice sheet feedbacks and to investigate the transient response of the climate system over a complete ice age cycle.
