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Antarctic Climate Change and Stratospheric Ozone Depletion. Karen L. Smith Lamont-Doherty Earth Observatory Earth 2 Class October 19, 2013. Antarctic Climate Change. Antarctic climate change over the past several decades has been dominated by the effects of stratospheric ozone depletion. - PowerPoint PPT Presentation
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Antarctic Climate Change and Stratospheric Ozone
Depletion
Karen L. SmithLamont-Doherty Earth Observatory
Earth 2 ClassOctober 19, 2013
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
The Antarctic Ozone Hole (2012)
Movie courtesy of NASA: from the OMI instrument on board the AURA satellite
UNEP, The Ozone Story, 1998
Outline
• Introduction to Ozone• Ozone Depletion• The Montreal Protocol• ODP vs. GWP• Ozone and Climate• The “World Avoided”• Antarctic Sea Ice and Ozone
Introduction to Ozone
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
Atmospheric Pressure
0 0.2 0.4 0.6 0.8 1.00
4
8
12
16
20
24
28
32
36
40
Atmospheric Pressure (atm)
Altitude (km)
Mt. Everest
Denver
Commercial Airliners Troposphere
Stratosphere
Stealth Bomber
U2 Spy Plane
50
Weather BalloonsFelix Baumgartner
Thermal Structure of the Atmosphere
Ozone in the Atmosphere
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)
Ozone Absorption in the UV Band
• UV radiation includes wavelengths from 200 to 400 nm
• UV-A 320-400 nm• UV-B 200-320 nm• UV-C 200-290 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
Anthropogenic Ozone Depletion
CFC’s (1928) – Wonder Gas!
UNEP, The Ozone Story, 1998
CFC’s (1928) – Wonder Gas!
UNEP, The Ozone Story, 1998
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?
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
The Ozone Hole through Time
194 DU 108 DU
82 DU 118 DU
1979 1989
2006 2010
Ozonesondes
Ozonesonde Measurements 2012
Courtesy of NOAA
Ozone Hole Recovery?
Courtesy of NOAA
2012 Ozone Hole 2nd smallest in last 20 years!
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.
The Montreal Protocol
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 50% 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
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: …
Ratification of Montreal Protocol(July 2003)
Countries that have NOT Ratified the Montreal Protocol (11 Countries)
Ozone-Depleting Substances (ODS)
Ozone Assessment, 2010
The Montreal Protocol has slowed and reversed the emission and accumulation of ODSs in the stratosphere.
ODP vs. GWP
Radiative Forcing (RF)
AR4, 2007
Radiative Forcing (RF)
AR4, 2007
Radiative Forcing (RF)
AR4, 2007
ODP and GWP
The Montreal Protocol has a dual benefit: protecting ozone and climate!
Ozone Assessment, 2010
Mass-Weighted Emissions
ODP-Weighted Emissions
GWP-Weighted Emissions
Montreal Protocol Protects Climate
Ozone Assessment, 2010; Velders 2007
3.0
Ozone Depletion Offset
0.9
HFC Offset
Montreal Protocol decreases CO2-eq emissions by 11 Gt in 2010!
~11 Gt
N.B. The reduction target for the Kyoto Protocol for 2008-2012 is 2 Gt.
Ozone and Climate
Geopotential Height Trends and the Southern Annular Mode of Variability
Thompson and Solomon 2002
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)
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)
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)
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)
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)
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)
20th Century Change:Attribution to Ozone and GHG
Polvani et al. 2011a
20th Century Change:Attribution to Ozone and GHG
Polvani et al. 2011a
21st Century Change:Attribution to Ozone and GHG
Polvani et al. 2011b
The “World Avoided”
The “World Avoided”
EECL – Equivalent effective Chlorine
(think of it as CFC’s)
“No Montreal Protocol”
Garcia et al., 2012
“World Avoided” Global Warming21st Century Ts Change
(a) Control (Montreal Protocol)
(b) “World Avoided” (No Montreal Protocol)
(c) Averaged Over Longitudes
Garcia et al., 2012
UV Index
Values over 11 are considered “extreme”
Present-day levels of ozone
“World Avoided”
Garcia et al., 2012
Ozone Depletion and Antarctic Sea Ice
Antarctic sea ice extent is increasing
Small + positive trend in Antarctic sea ice
Data: NSIDC; http://www.columbia.edu/~mhs119/UpdatedFigures/
What about changes in other components of the Antarctic climate system?
Sea Ice
Is there a connection between trends in stratospheric ozone depletion and the observed trend in Antarctic sea ice?
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
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 (2001-2065) 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.
Stratospheric ozone recovers in RCP 4.5
October-November-December Polar Cap Total Column Ozone
2001 2011 2021 2031 2041 2051 2061 Year
Dobs
on U
nits
Ozone recovery mitigates Antarctic sea ice loss
Austral Autumn Sea Ice Extent
Monthly sea ice extent response (FixODS – RCP4.5)
Absolute Difference Relative Difference
Resp
onse
(106 k
m2 )
Clim
atol
ogy
106 k
m2
Resp
onse
(%)
Month Month
Monthly sea ice extent response (FixODS – RCP4.5)
Absolute Difference Relative Difference
Resp
onse
(106 k
m2 )
Clim
atol
ogy
106 k
m2
Resp
onse
(%)Annual Mean Response to
climate change in RCP4.5: ~-11%Annual Mean Response to Fixed Ozone: ~-4%
Month Month
Monthly sea ice extent response (FixODS – RCP4.5)
Absolute Difference Relative Difference
Resp
onse
(106 k
m2 )
Clim
atol
ogy
106 k
m2
Resp
onse
(%)
Month Month
Ozone recovery decreases magnitude of SIE loss by: ~33%
Fixing ODS’s leads to a poleward shift in the large-scale atmospheric circulation
Summer Zonal Mean Zonal Wind Response
Contour interval is 1 m/s. Gray shading indicates 95% statistical significance.
Pres
sure
(hPa
)
Latitude
Poleward shifted surface Westerlies induce a surface wind stress response
• Sea ice concentration response (%; shading) • Surface wind stress(black vectors)
• Surface temperature(black curves)
Summer
Ozone depletion induces Ekman-driven oceanic meridional overturning circulation
Summer
Upper ocean warming persists throughout the year
Summer Autumn
Winter Spring
The Southern Ocean response to fixing ODS’s
Sea Ice
Meridional Overturning Circulation
Atmosphere
Ocean
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
How do we reconcile models and observations?
• Observations: sea ice is increasing
• Models: both GHG and stratospheric ozone depletion melt sea ice!
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!
Natural variability?
27-year trends are highlighted
Natural variability?
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.
References
• UNEP, Ozone Assessment 2010: http://ozone.unep.org/Assessment_Panels/SAP/Scientific_Assessment_2010/index.shtml
• NASA Ozone Watch: http://ozonewatch.gsfc.nasa.gov/• US EPA: http://www.epa.gov/ozone/strathome.html• 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
Thank you!