1. Antarctic Climate Change and Stratospheric Ozone Depletion
Karen L. Smith
Lamont-Doherty Earth Observatory
Earth 2 Class
October 19, 2013

2. Antarctic Climate Change
Antarctic climate change over the past several decades has been dominated by the effects of stratospheric ozone depletion
Thompson et al. 2011

3. The Antarctic Ozone Hole (2012)
Movie courtesy of NASA: from the OMI instrument on board the AURA satellite

4. Outline Introduction to Ozone Ozone Depletion The Montreal Protocol
ODP vs. GWP
Ozone and Climate
The “World Avoided”
Antarctic Sea Ice and Ozone
UNEP, The Ozone Story, 1998

5. Introduction to Ozone

6. Ozone (O3) Blue colored, strong smelling molecule Absorbs UV radiation
Unstable: constantly breaks down, reforms in stratosphere
Breakdown can be accelerated by certain chemicals (catalysts)
Also a primary constituent of photochemical smog in the troposphere

7. Atmospheric Pressure Stratosphere Felix Baumgartner Troposphere
Altitude (km) 50
Stratosphere
Felix Baumgartner 40
Weather Balloons 36 32
U2 Spy Plane 28 24 20
Stealth Bomber 16
Commercial Airliners
Troposphere 12
Mt. Everest 8 4
Denver
0.2
0.4
0.6
0.8
1.0
Atmospheric Pressure (atm)

8. Thermal Structure of the Atmosphere

9. Ozone in the Atmosphere

10. Ozone Formation in the Atmosphere
Solar radiation striking the Earth’s atmosphere is absorbed by air molecules
O2 strongly absorbs in the UV band
Absorption of UV by molecular oxygen splits the O=O bond, forming O free radicals
These O free radicals combine with molecular oxygen to form O3 (ozone)

11. Ozone Absorption in the UV Band
UV radiation includes wavelengths from 200 to 400 nm
UV-A nm
UV-B nm
UV-C nm
UV-C
Nearly all UV-C is absorbed in the upper atmosphere
UV-B
90% of UV-B is absorbed by the atmosphere, mostly by O3
UV-A
Not strongly absorbed by the atmosphere

12. Anthropogenic Ozone Depletion

13. CFC’s (1928) – Wonder Gas!
UNEP, The Ozone Story, 1998

14. CFC’s (1928) – Wonder Gas!
UNEP, The Ozone Story, 1998

15. Stratospheric Ozone Depletion
Results from large-scale industrial manufacture and release of synthetic compounds (chlorofluorocarbons, CFCs) in quantities that can interfere with chemical processes in the Earth’s atmosphere
Unanticipated side effects of CFCs – like acid rain, global warming, etc., were not expected… only appreciated in hindsight
Environmental “success” story?

16. Polar Ozone Destruction
“Ozone Hole”: term for regional, seasonal thinning of O3 layer over the poles
Cause: catalytic destruction of O3 by Cl and Br
Mechanisms are complex:
Ice clouds form in frigid stratospheric winter air, absorb HNO3, ClONO2, HCl
Surface reactions on ice convert these to reactive Cl2, HOCl, which accumulate, trapped in ice
Spring daylight returns, solar radiation converts Cl2 to Cl and HOCl to HO· and Cl
Sudden burst of Cl· reacts with O3, produces ClO· which forms ClO-OCl, which forms ClOO· and Cl·
Abundant Cl destroys lots of ozone
Chain is broken when sunlight evaporates polar clouds , releasing bound HNO3; NO2 reacts with ClO· and traps it again

17. The Ozone Hole through Time
194 DU
108 DU
1979
1989
82 DU
118 DU
2006
2010

18. Ozonesondes

19. Ozonesonde Measurements 2012
Courtesy of NOAA

20. Ozone Hole Recovery? 2012 Ozone Hole 2nd smallest in last 20 years!
Courtesy of NOAA

21. Ozone and UV
Ozone in the atmosphere is directly correlated with the UV intensity at the Earth’s surface
Most of the biologically harmful effects of ozone depletion are due to an increase in UV-B at the Earth’s surface.
Too much UV-B at the Earth’s surface can lead to an increase in skin cancer, cataracts and other health problems.

22. The Montreal Protocol

23. History 1974: Molina & Rowland (1974) Nature 249, 810-812
Paper calls attention to dangers of CFC’s in ozone breakdown
1978: U.S., Canada, Sweden and Norway ban CFCs as propellants
1987: Montreal Protocol calls for decrease in CFCs to % of 1986 levels by 1999
1990: London Amendments call for complete CFC phase-out by 2000
1992: Copenhagen Amendments accelerate phase-out to 1996
1995: Molina & Rowland win Nobel Prize in Chemistry

24. Montreal Protocol (1987)
The 1987 Montreal Protocol on Substances that Deplete the Ozone Layer (as agreed in 1987)
Preamble
The Parties to this Protocol,
Being Parties to the Vienna Convention for the Protection of the Ozone Layer,
Mindful of their obligation under that Convention to take appropriate measures to protect human health and the environment against adverse effects resulting or likely to result from human activities which modify or are likely to modify the ozone layer,
Recognizing that world-wide emissions of certain substances can significantly deplete and otherwise modify the ozone layer in a manner that is likely to result in adverse effects on human health and the environment,
Conscious of the potential climatic effects of emissions of these substances,
Aware that measures taken to protect the ozone layer from depletion should be based on relevant scientific knowledge, taking into account technical and economic considerations,
Determined to protect the ozone layer by taking precautionary measures to control equitably total global emissions of substances that deplete it, with the ultimate objective of their elimination on the basis of developments in scientific knowledge, taking into account technical and economic considerations,
Acknowledging that special provision is required to meet the needs of developing countries for these substances,
Noting the precautionary measures for controlling emissions of certain chlorofluorocarbons that have already been taken at national and regional levels,
Considering the importance of promoting international co-operation in the research and development of science and technology relating to the control and reduction of emissions of substances that deplete the ozone layer, bearing in mind in particular the needs of developing countries,
HAVE AGREED AS FOLLOWS: …

25. Ratification of Montreal Protocol (July 2003)
Countries that have NOT Ratified the Montreal Protocol (11 Countries)

26. Ozone-Depleting Substances (ODS)
The Montreal Protocol has slowed and reversed the emission and accumulation of ODSs in the stratosphere.
Ozone Assessment, 2010

27. ODP vs. GWP

28. Radiative Forcing (RF)
AR4, 2007

29. Radiative Forcing (RF)
AR4, 2007

30. Radiative Forcing (RF)
AR4, 2007

31. ODP and GWP
The Montreal Protocol has a dual benefit: protecting ozone and climate!

32. Mass-Weighted Emissions
ODP-Weighted Emissions
GWP-Weighted Emissions
Ozone Assessment, 2010

33. Montreal Protocol Protects Climate
Montreal Protocol decreases CO2-eq emissions by 11 Gt in 2010!
Ozone Depletion Offset
HFC Offset
3.0
0.9
~11 Gt
N.B. The reduction target for the Kyoto Protocol for is 2 Gt.
Ozone Assessment, 2010; Velders 2007

34. Ozone and Climate

35. Geopotential Height Trends and the Southern Annular Mode of Variability
Thompson and Solomon 2002

36. Climate Change Attribution
How do we attribute climate changes to greenhouse gases versus ozone depletion?
Use a global climate model, e.g.)
Table of GCM simulations (Polvani et al., 2011)

37. Climate Change Attribution
How do we attribute climate changes to greenhouse gases versus ozone depletion?
Use a global climate model, e.g.)
Table of GCM simulations (Polvani et al., 2011)

38. Climate Change Attribution
How do we attribute climate changes to greenhouse gases versus ozone depletion?
Use a global climate model, e.g.)
Table of GCM simulations (Polvani et al., 2011)

39. Climate Change Attribution
How do we attribute climate changes to greenhouse gases versus ozone depletion?
Use a global climate model, e.g.)
Table of GCM simulations (Polvani et al., 2011)

40. Climate Change Attribution
How do we attribute climate changes to greenhouse gases versus ozone depletion?
Use a global climate model, e.g.)
Table of GCM simulations (Polvani et al., 2011)

41. Climate Change Attribution
How do we attribute climate changes to greenhouse gases versus ozone depletion?
Use a global climate model, e.g.)
Table of GCM simulations (Polvani et al., 2011)

42. 20th Century Change: Attribution to Ozone and GHG
Polvani et al. 2011a

43. 20th Century Change: Attribution to Ozone and GHG
Polvani et al. 2011a

44. 21st Century Change: Attribution to Ozone and GHG
Polvani et al. 2011b

45. The “World Avoided”

46. The “World Avoided” “No Montreal Protocol” EECL –
Equivalent effective Chlorine
(think of it as CFC’s)
Garcia et al., 2012

47. “World Avoided” Global Warming
21st Century Ts Change
Control (Montreal Protocol)
“World Avoided” (No Montreal Protocol)
Averaged Over Longitudes
Garcia et al., 2012

48. UV Index “World Avoided” Values over 11 are considered “extreme”
Present-day levels of ozone
Garcia et al., 2012

49. Ozone Depletion and Antarctic Sea Ice

50. Antarctic sea ice extent is increasing
Small + positive trend in Antarctic sea ice
Data: NSIDC;

51. What about changes in other components of the Antarctic climate system?
Sea Ice

52. Is there a connection between trends in stratospheric ozone depletion and the observed trend in Antarctic sea ice?

53. Future Antarctic sea ice loss
GCM simulations using Whole Atmosphere Community Climate Model Version 4 (WACCM4; Marsh et al. 2012)
1.9 x 2.5° horizontal resolution
66 vertical levels up to 140 km
coupled middle atmosphere chemistry
coupled ocean and sea ice components

54. Future Antarctic sea ice loss
GCM simulations using Whole Atmosphere Community Climate Model Version 4 (WACCM4; Marsh et al. 2012).
1.9 x 2.5° horizontal resolution
66 vertical levels up to 140 km
coupled middle atmosphere chemistry
coupled ocean and sea ice components
Two 3-member ensembles of 21st century ( ) integrations with and without ozone recovery.
1st Ensemble, RCP4.5: Standard RCP 4.5 including ozone recovery.
2nd Ensemble, FixODS: RCP 4.5 with surface ozone-depleting substances fixed at year 2000 levels.
Response is ensemble mean FixODS – RCP4.5 averaged over last 10 years of integration.

55. Stratospheric ozone recovers in RCP 4.5
October-November-December Polar Cap Total Column Ozone
Dobson Units
Year

56. Ozone recovery mitigates Antarctic sea ice loss
Austral Autumn Sea Ice Extent

57. Monthly sea ice extent response (FixODS – RCP4.5)
Absolute Difference
Relative Difference
Response (106 km2)
Response (%)
Climatology 106 km2
Month
Month

58. Monthly sea ice extent response (FixODS – RCP4.5)
Absolute Difference
Relative Difference
Annual Mean Response to climate change in RCP4.5: ~-11%
Annual Mean Response to Fixed Ozone: ~-4%
Response (106 km2)
Response (%)
Climatology 106 km2
Month
Month

59. Monthly sea ice extent response (FixODS – RCP4.5)
Absolute Difference
Relative Difference
Ozone recovery decreases magnitude of SIE loss by: ~33%
Response (106 km2)
Response (%)
Climatology 106 km2
Month
Month

60. Fixing ODS’s leads to a poleward shift in the large-scale atmospheric circulation
Summer Zonal Mean Zonal Wind Response
Pressure (hPa)
Latitude
Contour interval is 1 m/s. Gray shading indicates 95% statistical significance.

61. Poleward shifted surface Westerlies induce a surface wind stress response
Summer
Sea ice concentration response (%; shading)
Surface wind stress
(black vectors)
Surface temperature
(black curves)

62. Ozone depletion induces Ekman-driven oceanic meridional overturning circulation
Summer

63. Upper ocean warming persists throughout the year
Summer
Autumn
Winter
Spring

64. The Southern Ocean response to fixing ODS’s
Atmosphere
Sea Ice
Ocean
Meridional Overturning Circulation

65. Robust response in models to stratospheric ozone perturbations
Three different modeling studies that show Antarctic sea ice decreases in the presence of an ozone hole:
Sigmond and Fyfe (2010)
stratosphere-resolving GCM; ocean eddies parameterized.
Smith et al. (2012)
stratosphere-resolving GCM with interactive middle atmosphere chemistry; ocean eddies parameterized.
Bitz and Polvani (2012)
standard low-top GCM with resolved ocean eddies

66. How do we reconcile models and observations?
Observations: sea ice is increasing
Models: both GHG and stratospheric ozone depletion melt sea ice!

67. How do we reconcile models and observations?
Observations: sea ice is increasing
Models: both GHG and stratospheric ozone depletion melt sea ice!
LARGE INTERNAL VARIABILITY!

68. Natural variability?
27-year trends are highlighted

69. Natural variability?

70. Conclusions
The Montreal Protocol is one of the great success stories of international climate protection policy.
Scientists and policy-makers have regulated the dual protection of the ozone layer and the climate.
The climate of the Antarctic has changed dramatically as a consequence of ozone depletion. Future changes will reflect both ozone recovery and GHG warming.

71. References
UNEP, Ozone Assessment 2010:
NASA Ozone Watch:
US EPA:
The Ozone Story, UNEP, 1998
Velders et al., PNAS 2007
Polvani et al., J. Climate, 2011
Polvani et al., GRL, 2011
Smith et al., GRL, 2012
Kang et al., Science, 2011
Garcia et al., JGR, 2012
Wu et al., J. Climate, 2013
Smith et al. , GRL, 2012
Polvani and Smith, GRL, 2013

72. Thank you!