Simulations of anthropogenic change in the strength of the Brewer-Dobson circulation

All the models reproduce the observed upwelling across the tropical tropopause balanced by downwelling in the extra tropics, though the seasonal cycle in upwelling in some models is more semi-annual than annual.

All the models also consistently predict an increase in the mass exchange rate in response to growing greenhouse gas concentrations, irrespective of whether or not the model includes interactive ozone chemistry. The mean trend is 11 kt s⁻¹ year⁻¹ or about 2% per decade but varies considerably between models. In all but one of the models the increase in mass exchange occurs throughout the year though, generally, the trend is larger during the boreal winter.