1. Links between ozone and climate 9 th ORM Geneva, 14 May 2014 SAP Co-chairs Ayité-Lô Ajavon (Togo) Paul Newman (USA) John Pyle (UK) A.R. Ravishankara (USA)

2. Chapter 4 of the upcoming assessment deals with “Stratospheric ozone changes and climate”. Chapters 1 and 5 discuss ODS, their replacements and consider various climate metrics.

3. Ozone/climate interactions Atmospheric ozone is affected by climate change Transport and temperature-dependent chemical processes Atmospheric ozone can affect climate New evidence on how stratospheric ozone changes influence tropospheric weather and climate Climate role of ozone depleting substances and their replacements

4. Atmospheric ozone is affected by climate change Increases in CO 2 cool the stratosphere Slows down the rate of gas-phase ozone destruction  O 3 increase Tendency to increase loss in polar latitudes Increase in GHGs changes the stratospheric circulation Changed circulation changes stratospheric ozone distribution. Enhanced stratosphere to troposphere transport.

5. Models project a strengthening of the Brewer-Dobson circulation under climate change

6. Ozone change is dependent on GHG scenario From Eyring et al, 2013 NB: N 2 O and CH 4 are chemically active GHGs

7. Atmospheric ozone can affect climate Ozone is a GHG and also absorbs solar radiation Stratospheric ozone loss is dominant drive of observed cooling in the lower stratosphere Stratospheric ozone loss likely the dominant driver of SH circulation changes in recent decades and has led to various climate effects Intensification of the summer westerlies; changes in the Southern Annular Model; Hadley Cell expansion; precipitation changes, etc. No clear links to climate trends in NH

8. Eyring et al, 2013 Ozone loss a major driver of lower stratospheric temperature trends

9. Eyring et al, 2013 Observed trends in the SH jet are only reproduced by models including observed ozone loss

10. ODSs and replacements are GHGs

11. Radiative forcing from ODS and replacements Projections show different scenarios Rigby et al, GRL, 2014

12. Because of the impact of GHGs on the troposphere and stratosphere, reduction of ODS will not return the ozone layer exactly to its 1980 value  need for continued measurements of ozone vertical profile. Increasing GHGs alter transport of ozone and other species in the stratosphere  need to measure profiles of atmospheric tracers, like N 2 O, SF 6, etc. Stratosphere projected to cool because of GHGs  need to measure temperature profiles into the upper stratosphere Some conclusions