Simulated lower stratospheric trends between 1970 and 2005: Identifying the role of climate and composition changes

The simulations were performed using a version of the Community Atmosphere Model version 3 (CAM3) updated with interactive tropospheric and stratospheric chemistry. Even with a relatively low model top (≈40 km), this model shows good ability at reproducing a variety of large-scale changes in climate and chemical composition in the stratosphere when forced with the observed sea-surface temperatures and surface concentrations of long-lived trace gases and ozone-depleting substances.

We then used the same model framework to differentiate the role of chemically active composition (ozone, methane, and chlorofluorocarbons) and CO₂ changes on observed trends in the stratosphere. Among the sensitivity factors analyzed, our simulations indicate that changes in CO₂ over the simulated period do not lead to significantly different total ozone trend; however, changes in CO₂ lead to important differences in ozone in the upper part of the model.