Chlorine and Ozone Recovery in CCMs

Changes in stratospheric chlorine play a major role in long-term changes of ozone, and it is important that coupled chemistry-climate models (CCMs) correctly model the time evolution of stratospheric chlorine. We examine here the evolution of inorganic chlorine (Cly) and ozone (O3) in the polar lower stratosphere of CCMs participating in the CCM Validation Activity. It is found that there are substantial quantitative differences between the simulations of Cly, with the peak value varying from less than 2 ppb to over 3.5 ppb, and the date at which the Cly returns to 1980 values varying from before 2030 to after 2050. There is a corresponding large range in the timing of recovery of Antarctic ozone back to 1980 values, and models with an earlier Cly recovery generally have an earlier ozone recovery. This agreement indicates that the differences in Cly between models are key to diagnosing the inter-model differences in simulated ozone hole recovery.