Towards fast machine learning parameterizations of stratospheric ozone feedbacks in climate change simulations
Authors: Nowack Peer , Abraham Nathan Luke , Braesicke Peter 
Published: March 2020

&lt;p&gt;There is a plethora of ways in which the representation of upper tropospheric and stratospheric ozone (&amp;#8216;ozone feedbacks&amp;#8217;) can affect the outcome of climate change simulations. Prominent examples include modulations of the tropospheric and stratospheric circulation, climate sensitivity, cloud formation, and stratospheric water vapour (e.g. [1-8]). Here I first revisit some recent work providing evidence for such effects. I then provide an update on a recently developed machine learning parameterization for ozone using the UK Earth System Model (UKESM1, [9]). Such a parameterization could adequately represent ozone feedbacks without adding the high computational expense of a fully interactive atmospheric chemistry scheme. The parameterization could also provide several notable scientific advantages, for example concerning the treatment of important chemistry-climate model biases. Finally, I put my results into the context of several other methods suggested as potential means for addressing ozone-related effects in idealized climate sensitivity simulations, also considering the still substantial uncertainties related to modelling ozone [10,11] and associated climate feedbacks [5,12].&lt;/p&gt;&lt;p&gt;References:&lt;/p&gt;&lt;p&gt;[1] Son et al. (2008), The impact of stratospheric ozone recovery on the Southern Hemisphere westerly jet. Science 320, 1486, doi:10.1126/science.1155939.&lt;/p&gt;&lt;p&gt;[2] Dietm&amp;#252;ller et al. (2014), Interactive ozone induces a negative feedback in CO2-driven climate change simulations, Journal of Geophysical Research: Atmospheres 119, 1796-1805, doi:10.1002/2013JD020575.&lt;/p&gt;&lt;p&gt;[3] Chiodo &amp; Polvani (2016), Reduction of climate sensitivity to solar forcing due to stratospheric ozone feedback, Journal of Climate 29, 4651-4663, doi:10.1175/JCLI-D-15-0721.1.&lt;/p&gt;&lt;p&gt;[4] Chiodo &amp; Polvani (2017), Reduced Southern Hemispheric circulation response to quadrupled CO2 due to stratospheric ozone feedback, Geophysical Research Letters 43, 465-474, doi:10.1002/2016GL071011.&lt;/p&gt;&lt;p&gt;[5] Nowack et al. (2015), A large ozone-circulation feedback and its implications for global warming assessments. Nature Climate Change 5, 41-45, doi:10.1038/nclimate2451.&lt;/p&gt;&lt;p&gt;[6] Nowack et al. (2017), On the role of ozone feedback in the ENSO amplitude response under global warming, Geophysical Research Letters 44, doi:10.1002/2016GL072418.&lt;/p&gt;&lt;p&gt;[7] Nowack et al. (2018), The impact of stratospheric ozone feedbacks on climate sensitivity estimates. Journal of Geophysical Research: Atmospheres 123, 4630-4641, doi:10.1002/2017JD027943.&lt;/p&gt;&lt;p&gt;[8] Rieder et al. (2019), Is interactive ozone chemistry important to represent polar cap stratospheric temperature variability in Earth-System Models?, Environmental Research Letters 14, 044026, doi: 10.1088/1748-9326/ab07ff.&lt;/p&gt;&lt;p&gt;[9] Nowack et al. (2018), Using machine learning to build temperature-based ozone parameterizations for climate sensitivity simulations, Environmental Research Letters 13, 104016, doi:10.1088/1748-9326/aae2be.&lt;/p&gt;&lt;p&gt;[10] Chiodo &amp; Polvani (2019), The response of the ozone layer to quadrupled CO2 concentrations: implications for climate, Journal of Climate 31, 3893-3907, doi:10.1175/JCLI-D-17-0492.1.&lt;/p&gt;&lt;p&gt;[11] Keeble et al. (2020), Evaluating stratospheric ozone and water vapour changes in CMIP6 models from 1850-2100, Atmospheric Chemistry and Physics Discussions.&lt;/p&gt;&lt;p&gt;[12] Dacie et al. (2019), A 1D RCE study of factors affecting the tropical tropopause layer and surface climate. Journal of Climate 32, 6769-6782, doi:10.1175/JCLI-D-18-0778.1.&lt;/p&gt;