Ozone-temperature correlations as a method for detecting and attributing the beginning of ozone recovery

In the upper stratosphere, where ozone is controlled primarily by photochemical reactions, the mixing ratio of ozone is anti-correlated with the temperature. The anti-correlation occurs because of the temperature dependence of the catalytic ozone loss cycles and slope of the correlation is dependent on the relative contributions of the loss cycles, each with its own temperature sensitivity. The most important fact for this work is that the chlorine catalytic cycle is significantly less temperature sensitive than the other cycles. Increases in chlorine from chlorofluorocarbons (CFCs) over the last several decades have reduced the slope of the ozone-temperature correlation in the upper stratosphere and recovery of ozone will lead to an increase in that slope back towards the pre-CFC relationship. We suggest that this method can be used as an alternative approach to detecting and attributing expected future ozone recovery. Preliminary results indicate that the change in the ozone-temperature correlation can be seen in high-resolution profile data from the combination of LIMS, UARS MLS, Aura MLS, and Aura HIRDLS data.

Future ozone increases will be affected by both the recovery of ozone-depleting substances and the continued increase of greenhouse gases, notably CO2. Model simulations indicate that the slope of the ozone-temperature correlation is not affected by ozone increases due to increasing CO2. The results of this study show that use of ozone-temperature correlation slope allows the detection of the beginning of ozone recovery that can be directly attributed to the change in chlorine due to the reductions stemming from adherence to the Montreal Protocol.