antarctic climate change and stratospheric ozone depletion

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!