We analyze trends in the Southern Annular Mode in CMIP6 simulations. For
the period 1957-2014, simulated linear trends are generally consistent
with two observational references but seasonally in disagreement with
two other reconstructions of the SAM. Using a regression analysis
applied to model simulations with interactive ozone chemistry, a
strengthening of the SAM in summer is attributed completely to ozone
depletion because a further strengthening influence due to long-lived
greenhouse gases is fully counterbalanced by a weakening influence due
to stratospheric ozone increases associated with these greenhouse gas
increases. Ignoring such ozone feedbacks would yield comparable
contributions from these two influences, an incorrect result. In winter,
trends are smaller but an influence of greenhouse gas-mediated ozone
feedbacks is also identified. The regression analysis furthermore yields
significant differences in the attribution of SAM changes to the two
influences between models with and without interactive ozone chemistry,
with ozone depletion and GHG increases playing seasonally a stronger and
weaker, respectively, role in the chemistry models versus the
no-chemistry ones.