Coupling between Ozone and the Circulation: A Negative Feedback on Southern Hemispheric Climate Change

Due to computational constraints, interactive stratospheric ozone chemistry is commonly neglected in climate models participating in large inter-comparison projects. Therefore, a full representation of the coupling between ozone and the circulation in climate models is still lacking. The impact of this simplification on their response to external forcings remains largely unexplored.

In this work, we examine the importance of including interactive stratospheric ozone chemistry on the Southern Hemispheric circulation response to CO2 forcing. Stratospheric ozone changes in these integrations occur in absence of any changes in ozone depleting substances, and can be thus considered as a true feedback. We find that interactive ozone largely reduces the response of the tropospheric mid-latitude jet to CO2, even though it does not alter the surface temperature response. The reduction of the Southern Hemispheric tropospheric circulation response is due to CO2 induced stratospheric ozone changes, and their effects on the meridional temperature gradient near the tropopause. It is shown that the coupling between ozone and the circulation provides a mechanism whereby the stratosphere can influence tropospheric climate change projections.

Our findings suggest that neglecting stratospheric ozone feedbacks results in an overestimate of the circulation response to increased CO2. This has wide implications for the climate change projections in the Southern Hemisphere, such as carbon uptake over the Southern Ocean, and the meridional circulation of the ocean.