Impact of Unmitigated HFC Emissions on Stratospheric Ozone at the End of the 21st Century as Simulated by Chemistry-Climate Models

Hydrofluorocarbons (HFCs) have been increasingly replacing chlorofluorocarbons and hydrochlorofluorocarbons. Although their direct chemical ozone-depleting potential is negligible, as potent greenhouse gases they modify atmospheric temperature and circulation patterns, thereby indirectly influencing stratospheric ozone recovery. Measurements and model projections must continue to evaluate HFC limitation measures and assess the long-term impact of HFCs on the atmospheric radiation budget and stratospheric ozone. In this study, we present multi-member ensemble simulations designed to estimate the impact of HFCs on stratospheric temperature, ozone and circulation changes at the end of the century. We compared simulations with and without HFCs for two three-dimensional chemistry-climate models that use the same chemistry module but different physical schemes. At low and mid-latitudes, temperature and ozone responses were comparable for both models and in general agreement with previous studies. HFCs induced a marked temperature increase up to about 10-20 hPa and vertically alternating positive and negative ozone anomalies. We explained this pattern by competing effects of vertical motion (low and middle stratosphere) and temperature (upper stratosphere) anomalies. At northern high latitudes, there were strong discrepancies with previous studies and between the models themselves, attributed to differences in ozone anomalies caused by wave activity during winter. Quantitatively, we found a net positive, but small, HFC impact on total ozone amounts. Largest anomalies were less than 1% in the winter polar stratosphere. Our results indicate that increasing HFC amounts will likely have a limited impact on stratospheric ozone recovery within this century, with large uncertainty in the polar regions.

Automated summary

HFCs have a limited impact on stratospheric ozone recovery, with similar simulations in low and mid-latitudes but significant discrepancies in northern high latitudes. The competing effects of vertical motion and temperature anomalies contribute to the observed patterns in the stratosphere.