What drives the impact of global warming on stratospheric ozone in the tropics?

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Aaron Match just submitted a very elegant paper on the impact of global warming on ozone in the tropical stratosphere to GRL! Combining the classic leaky pipe model of the stratosphere with Chapman photochemistry and a simple representation of tropospheric ozone destruction, we show that the apparant upward shift of ozone in response to global warming is actually due to fortituous overlap of several different processes.

The ozone layer absorbs ultraviolet light otherwise harmful to life. Due to the Montreal Protocol, the ozone layer is generally recovering from depletion. In response to global warming, ozone is predicted to increase in the upper stratosphere but decrease in the tropical lower stratosphere. These decreases have previously been attributed to strengthening of stratospheric upwelling or to the deepening of the troposphere under global warming. We draw on elements of these prevailing explanations to quantify a new mechanism, which explains roughly half of the decrease: deepening of the troposphere converts stratospheric air into tropospheric air, the low ozone anomalies from which are then transported upwards into the tropical lower stratosphere by the background upwelling.