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Conclusions

• The model predicts an overall cooling of the stratosphere which increases with height.
• In the polar stratosphere quantitative temperature trends are unpredictable due to unpredictable decadal variability in the planetary wave driving from the troposphere.
• The model predicts an increase in the flux of planetary wave activity emanating from the troposphere, especially in the sub-tropics.
• No significant change is predicted in the direction of the EP flux in the sub-tropical lower stratosphere.
• The model correctly reproduces the Brewer-Dobson circulation with the mass fluxes between the stratosphere and troposphere broadly in agreement with observational estimates.
• The mass exchange rate between the stratosphere-troposphere is predicted to increase by 3% per decade.
• The increases in the mass exchange rate occur in all seasons (e.g. there is no change in the amplitude of the annual cycle in the tropical tropopause temperatures.
• By downward control the increased mass fluxes can be accounted for by the increased planetary wave-driving resulting from extra wave activity emanating from the troposphere.
• Change in the direction of wave propagation do not appear to be significant factor in the stratosphere.
• The increases in the mass exchange rate between the troposphere-stratosphere are of particular relevance to ozone and climate prediction because of the effects on the removal of chlorofluorocarbons (CFCs) and other GHGs from the atmosphere (Butchart & Scaife 2000).