1. Controls on the Past and Future Depletion of Antarctic Ozone and the Emergence of Healing
Susan Solomon
Richards Professor of Atmospheric Chemistry and Climate Science, MIT
Based on work with many including Diane Ivy, Justin Bandoro - (MIT)
Doug Kinnison, Mike Mills, Ryan Neely, Rolando Garcia - (NCAR),
Anja Schmidt - (U. Leeds, UK)
The emergence of healing in the Antarctic ozone hole: an early season phenomenon
Understanding the record hole of Oct 2015 and the key role of volcanoes

2. 2015! Three stages of ozone recovery (WMO/UNEP): Rate of decline slows
Ozone is flat instead of worsening (in ‘remission’)
Ozone increases -- and in a manner that can be attributed to halogen decreases (healing)
2015!

3. Attribution of Global Global Change
Natural and human effects
IPCC (1995):
“Balance of evidence suggests discernible human influence”
IPCC (2001):
“Most of global warming of past 50 years likely (odds 2 out of 3) due to human activities”
IPCC (2007):
“Most of global warming of past 50 years very likely (odds 9 out of 10) due to greenhouse gases”
Agung
Chichon
Pinatubo
Observations
Natural forcings only
Variability and fingerprinting…a similar approach can be taken for ozone attribution

4. Ozone: A Tale of Chlorine and Aerosol
Solomon et al., JGR, 2005

5. Ozonesondes and volcanic signatures – Solomon, Portmann, Hofmann and others
Signals of Pinatubo in lower
stratosphere
South Pole
2015, after Calbuco showed lowest values in this region since Pinatubo

6. Attribution of Polar Ozone Healing
Do the data suggest that ozone is increasing?  SBUV, TOMS/OMI, South Pole station, South Pole and Syowa sondes. Profile, depth of ozone loss, area of ozone hole? Seasonal cycles of each?
How can we analyze dynamical or thermal variability or trends?  use SD-WACCM, nudged to MERRA meteorological data reanalyses (T’s and circulation obs-driven)
What about volcanic changes in PSCs and aerosols  use model of sulfur injections from all known volcanoes (since observations of PSCs and aerosols are too limited).
Compare with data: SD-WACCM - CCMI run prior to 1999, then three sets of model runs from 1999 on:
(i) chem/dyn/volc - all changing with time
(ii) vol-clean – chem/dyn changing, volcanically clean
(iii) chem-only (fixed 1999 dyn (and temperatures); and volcanically clean)

7. Depth of the Antarctic Total Ozone Loss
South Pole
SBUV polar cap
South Pole
SBUV polar cap
October avg – highly variable. Well simulated by model. No statistically significant healing trend (90% confidence).
September avg – healing suggested ✔✔
[Notes: No months show significant healing in the Arctic not included in Antarctic trend analyses]
From Solomon et al., Science, 2016.

8. Profile of the Antarctic Ozone Loss
What is the role of ozone/temperature feedback?
More ozone  warmer less depletion
SD-WACCM uses observed temperatures, so any such contributions are credited to chem/dyn/vol here, even those that are chemically driven.
Depletion
Healing
Shape of the trend in the September profile of increased concentrations since 2000, at two different stations. ✔✔✔
Model suggests as a best estimate that about half of the September recovery near 15 km is chemical (while half is dynamics/temperature). But within uncertainties ≈100% may be chemical.
Solomon et al., Science, 2016.

9. What about the size of the hole?
Observations
Model including chlorine, meteorology, and volcanoes record well reproduced with Calbuco (but not without it)
From Solomon et al., Science, 2016.

10. Why is Cly key in the early season (but less so later)?
Early season  ClO is easily activated; ozone loss rate depends mainly on Cly, sunlight
Late season  ozone already driven close to zero in vortex core; ClO deactivation competes w/activation; the aerosol, T, and transport variability all can play larger roles
Hoppel et al., JGR, 2005

11. What About the Size of the Hole?
(and stays above > 3 days)
The ozone hole is starting to heal in the early season. ✔✔✔
From Solomon et al., Science, 2016.
Ups and downs are well reproduced. The ozone hole is opening more slowly on average, even in cold and/or volcanically-perturbed years.
Affects the monthly average for September -- but by October the hole has had enough time to be fully formed, and is more sensitive to other factors besides Cly.

12. Conclusions/Discussion
• Antarctic ozone layer is starting its slow healing process in September (but not in October), based on multiple consistent fingerprints in seasonal ozone hole depth, profile with height, and area.
• Signs of chemical healing can be identified along with important contributions from dynamics/temperature. How large are chemical/radiative/dynamical feedbacks?
Net production
Net loss
• Key chemistry occurs in lowermost stratosphere/upper troposphere (between about km), from the vortex edge to the core. Role of water vapor variability?