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Abstract:
The important role of stratospheric feedbacks for the climate system – most notably how the ozone layer responds to anthropogenic forcings, and how that response then feeds back on the climate itself – remains largely unexplored, apart from the effects associated with gases regulated by the Montreal Protocol. This is because most models participating to CMIP inter-comparisons do not account for the complex interplay between stratospheric composition, dynamics and radiation. Here, we provide a review of recent work highlighting the importance of such interplay on a broad range of time-scales, encompassing short-term (i.e. intra-seasonal) variability to long-term climate change. First, we show that increasing carbon dioxide levels lead to substantial changes in the ozone layer and that these changes have a substantial effect on the circulation response to that forcing in both hemispheres. Then, we explore the connection between Arctic ozone and surface climate on inter-annual time-scales, highlighting the contribution of springtime ozone depletion to surface anomalies. Lastly, we show the impacts of long-term ozone recovery on the Arctic stratosphere and stratosphere-troposphere coupling; most remarkably, we find that ozone recovery significantly offsets the effects of GHGs on the polar vortex. Such findings demonstrate that stratospheric composition feedbacks play a key role in shaping the climate response to anthropogenic forcings, both via radiative and dynamical processes. However, the coupling between ozone, the large-scale atmospheric circulation and climate is still subject to large uncertainties. We discuss sources of uncertainty and model limitations in the simulation of these effects, and implications for CMIP6.
