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

Transcription

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 (O 3 ) 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 Altitude (km) Felix Baumgartner Weather Balloons Stratosphere U2 Spy Plane Stealth Bomber Commercial Airliners Mt. Everest Denver Atmospheric Pressure (atm) Troposphere

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 O 2 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 O 3 (ozone)

11 Ozone Absorption in the UV Band UV radiation includes wavelengths from 200 to 400 nm UV-A UV-B UV-C nm nm 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 O 3 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 O 3 layer over the poles Cause: catalytic destruction of O 3 by Cl and Br Mechanisms are complex: Ice clouds form in frigid stratospheric winter air, absorb HNO 3, ClONO 2, HCl Surface reactions on ice convert these to reactive Cl 2, HOCl, which accumulate, trapped in ice Spring daylight returns, solar radiation converts Cl 2 to Cl and HOCl to HO and Cl Sudden burst of Cl reacts with O 3, 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 HNO 3 ; NO 2 reacts with ClO and traps it again

17 The Ozone Hole through Time 194 DU 108 DU DU 118 DU

18 Ozonesondes

19 Ozonesonde Measurements 2012 Courtesy of NOAA

20 Ozone Hole Recovery? 2012 Ozone Hole 2 nd 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, 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 50% of 1986 levels by : London Amendments call for complete CFC phase-out by : Copenhagen Amendments accelerate phase-out to : 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 AR4, 2007 Radiative Forcing (RF)

29 AR4, 2007 Radiative Forcing (RF)

30 AR4, 2007 Radiative Forcing (RF)

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

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

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

44 21 st 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 21 st Century T s Change (a) Control (Montreal Protocol) (b) World Avoided (No Montreal Protocol) (a) 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 21 st century ( ) integrations with and without ozone recovery. 1 st Ensemble, RCP4.5: Standard RCP 4.5 including ozone recovery. 2 nd 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 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 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% Month Month

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

60 Fixing ODS s leads to a poleward shift in the large-scale atmospheric circulation Summer Zonal Mean Zonal Wind Response 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: ent_2010/index.shtml 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!