On the Role of Dynamical Uncertainties in the Spread of Arctic Ozone Recovery Projections

Arctic ozone is projected to recover over the 21st century in compliance with the Montreal Protocol. Chemistry-climate models show a large spread in recovery rates and future changes in key dynamical features such as the polar vortex and the residual circulation. Here, we quantify the spread in Arctic ozone recovery explained by uncertainties in these dynamical changes, using simulations from the Chemistry-Climate Model Initiative, phases 1 and 2022. About 60% of the spread in projected ozone recovery is attributed to differences in polar vortex trends and about one-third to the intermodel spread in residual circulation trends. Ozone-depleting substances and greenhouse gas-driven global warming contribute similarly to the spread in ozone recovery, although uncertainties in dynamical trends primarily affect the warming component. While dynamical changes clearly separate the simulated ozone recovery among different models, the large variability in the Arctic stratosphere precludes establishing an observational constraint on future ozone recovery.