The possible impact of doubling C02 on the zonal-mean zonal winds and the angular momentum of the atmosphere is examined using general circulation model output archived by the Goddard Institute for Space Studies, the National Center for Atmospheric Research, and the Geophysical Fluid Dynamics Laboratory. Whereas the emphasis in most previous studies with these models has been placed on the temperature and precipitation changes expected from a doubled-CO2 scenario, the intent here is to investigate some of the dynamical consequences predicted by them models, especially within the tropics where the zonal-wind and temperature changes are less tightly coupled than elsewhere.

Comparisons among the three models of the difference in zonal-mean zonal winds between 2×C02 and 1×C02 simulations indicate a common tendency when C02 is doubled for winds to become more easterly in much of the tropics during June-July-August. Less of a consensus for the tropics emerges for December-January-February, perhaps as a result of differences among the models' basic climatologies for the zonal-wind field. In general, however, changes predicted for the zonal winds in the tropics and elsewhere are comparable to the interannual variability currently observed, suggesting that these changes ought to become detectable eventually.

Largely because of the tropical wind changes, decreases in the troposphere's relative angular momentum accompany a doubling of C02 in all the model runs. The amplitude of the decrease is typically a considerable fraction of a model's seasonal cycle and, in some cases, is large enough that a measurable change in the length of day could result. Although the possibility of an anthropogenic effect on earth's rotation is noteworthy, such a prediction must be regarded as tentative in light of the shortcomings found in the models’ zonal-wind climatologies and the differences in their zonal-mean responses.