Changes of tracer distributions in the doubled CO2 climate

Changes in tracer distributions in the troposphere and stratosphere are cal culated from a control and doubled CO2 climate simulation run with the Godd ard Institute for Space Studies Global Climate Middle Atmosphere Model. Tra nsport changes are assessed using seven on-line tracers. Results show that interhemispheric transport is reduced by 5% along with a reduction in the H adley circulation. Tropical transport from the troposphere into the stratos phere increases by some 30% associated with an increase in the stratospheri c subtropical residual circulation. The tropical pipe becomes significantly more leaky, and greater transport into the lowermost stratosphere in the s ubtropics appears to be occurring, possibly in conjunction with a poleward shift in wave energy convergences. An increase in the high-latitude lower s tratosphere residual circulation reduces the stratospheric residence time o f extratropical injections such as bomb C-14 by 11%. Vertical mixing within the troposphere by convection increases, reducing low level concentrations of tracers. The Hadley cell change is affected by the latitudinal gradient of tropical warming. The high-latitude lower stratosphere residual circula tion change depends on the latitudinal gradient of the extratropical warmin g. Increased penetrating convection to the upper troposphere and the intens ified residual circulation in the tropical upper troposphere/lower stratosp here appear to be the most robust of these results, with a magnitude that d epends upon the degree of tropical warming. The consequence of this circula tion change is to increase trace gas concentrations in the stratosphere and to decrease them in the troposphere for those species that have tropospher ic sources.