Impact of unmitigated HFC emissions on stratospheric ozone at the end of
the 21st century as simulated by chemistry-climate models
Abstract
Hydrofluorocarbons (HFCs) have been increasingly replacing
chlorofluorocarbons and hydrochlorofluorocarbons. Although their
ozone-depleting potential is negligible, as potent greenhouse gases they
indirectly influence 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
5 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.