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Potential collapse of the West Antarctic Ice Sheet – Implications for global sea level rise
Nancy Bertler
2
The Challenge of Future Sea Level Rise
Victoria University of Wellington & GNS Science
IPCC Conclusions (AR5, 2013)
• up to 1m of global sea level rise by 2100 AD (RCP8.5)
• Or much more if the Antarctic Ice Sheets respond unpredictably
• 200 Million people live within 1m of present sea level
• Coastal inundation increases exponentially with linear sea level increase
Why could Antarctica respond unpredictably?
3
Victoria University of Wellington & GNS Science
IPCC Projections for 2100 AD
IPCC, AR5, WG1,Figure SPM 8
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Victoria University of Wellington & GNS Science
IPCC Sea Level Projections
Scenario Mean RangeRCP2.6 44 28-61RCP4.5 53 36-71RCP6.0 55 38-73RCP8.5 74 52-98
1m
0.5m
RCP 8.510mm/y
RCP 4.55mm/y
IPCC, AR5, 2013
5
Victoria University of Wellington & GNS Science
How to collapse an ice sheet?CH4 = 1950 ppbIn 2014
CO2 = 400 ppmIn 2014
Bertler & Barrett, 2011
image courtesy: Bob Bindschadler, NASA
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ANDRILLDirect evidence of West Antarctic Ice Sheet collapse events in the Pliocene
The Antarctic response to Pliocene warmth & implications for global sea-level
Victoria University of Wellington & GNS Science
Courtesy T. Naish
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Drill core evidence of past West Antarctic Ice Sheet collapse
(Naish et al, 2009; McKay et al., 2009)
Victoria University of Wellington & GNS Science
Record of Past Change - ANDRILL
Mid Pliocene, ~3-5M yr
• pCO2 at ~ 400 ppm• Global air temp 2-3°C warmer• S-Ocean temp 4-6°C warmer• Loss of West Antarctica, Greenland
and some East Antarctic margins• Sea level rise of 10-20m
Today’s pCO2 level: >400 ppm
Victoria University of Wellington & GNS Science
Today
Then
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Victoria University of Wellington & GNS Science
Pliocene surface warming response and polar amplification
Climate system equilibrium response to 405 ppm CO2 – mean temp = +2-3°C,Antarctic warming = +5-7°C
Surface Air Temperature
Haywood et al., (2012)
Global=+2.7°CPolar regions =+5-7°C
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Could Antarctica be even more sensitive ? – Data from
Greenland
NEEM Community Members, Nature, Jan 2013• Conditions during the Last Interglacial (LIG)
• pCO2 ~ 280ppm• NH temperature 1-2⁰C warmer than preindustrial • Sea level 4-8 m higher than today
• Greenland Ice Sheet contributed up to 2m• => 2-6 m from Antarctica’s marine based ice sheets
Victoria University of Wellington & GNS Science
Evidence of Antarctic Change Ice Shelf Collapse
The recent collapse of
– Wordie Ice Shelf (1966-1989)– Larsen Inlet (1989)– Mueller Ice Shelf (1999)– Larsen-A Ice Shelf (1995)– Prince Gustav Channel (1995)– Jones Ice Shelf (2003)– Larsen-B Ice Shelf (January 2003)– Wilkins Ice Shelf (March 2008, April 2009)
Victoria University of Wellington & GNS Science
Evidence of Antarctic Change – Warming Surface Temperature
Steig et al., Jan 2009, Nature
Victoria University of Wellington & GNS Science
Böning et al., Dec 2008, Nature
Evidence of Antarctic Change – Warmer Ocean
Victoria University of Wellington & GNS Science
• The ocean is warming to the sea floor
• 93% of human induced warming is absorbed by the ocean
Evidence of Antarctic Change – Sea Ice Trends
Victoria University of Wellington & GNS Science
IPCC AR5, 2013
• Antarctic ice loss increased fivefold from 1990s to today
• From marine based ice
• Dynamical ice discharge dominates (not melting)
Evidence of Antarctic Change – Mass Balance
Victoria University of Wellington & GNS Science
Bamber et al. 2012, BedmapBamber et al. Science 2009
~3.3m contribution to global sea level rise
Rignot et al. Nature, 2013
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Paolo et al., 2015, ScienceExpress
• WAIS mass loss – 70% increase in past 10 y
• Getz single biggest contributor (30% of WAIS ice shelve melt)
• AS/BS some ice shelves (i.e. Venable, Crosson) Lost ≤ 18% thickness in < 20 y
• Overall ~10-fold increase (from ~25±64km3/a to 310±74km3/a)
• Major driver: CDW intrusion
Accelerated Loss
Victoria University of Wellington & GNS Science
17
Data constraints – Agreement between different methods
Sutterley et al. 2014, GRL
• Good agreement• Acceleration by
16.3 Gt/yr2 (3x)
Victoria University of Wellington & GNS Science
18
Victoria University of Wellington & GNS Science
Marine ice sheet instability and rapid retreat
IPCC (2013); Schoof (2007)
BedMap2 = 22m equivalent SL of marine based ice(Fretwell et al., 2013)
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Joughin et al. 2014, ScienceRignot et al. 2014, GRL
Victoria University of Wellington & GNS Science
Point of No Return passed ?
Image courtesy Eric Rignot, JPL
Compounding mechanisms
Pollard et al. 2015, GRL
17m global sea level rise with 400ppm CO2
Victoria University of Wellington & GNS Science
21
data from Fleming et al. (1998)
How quickly can sea level rise?
Last iceage
Melt-water Pulse 1A = 4m/100yrs
Melt-waterPulse 1a
Sea level rise since the last ice age
First civilizationsin Europe/Asia
Victoria University of Wellington & GNS Science
New evidence that Antarctica could be a major contributor to MWP 1A, i.e.Weber et al. Nature 2014, Golledge et al. Nature Comm. 2014
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Is the current rate of sea level rise unusually high?
RCP 8.5
RCP 4.5
3.3 mm/y
10 mm/y
<1 mm/y
(IPCC AR5 2013)
(IPCC AR5 2013)
Victoria University of Wellington & GNS Science
Regional Pattern in Sea Level?
Victoria University of Wellington & GNS Science
(IPCC AR5 2013)
% Change from Average for 2081-2100 AD
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Changes in Occurrence Coastal Inundation
(IPCC AR5 2013)
The frequency of coastal inundation world-wide increases by a multiplier of 100 to 1000 times under RCP 4.5 scenario with 66% likelihood of ~ +50cm by 2100
Victoria University of Wellington & GNS Science
Changes in Occurrence Coastal Inundation for RCP 4.5
Victoria University of Wellington & GNS Science
Hunter et al. (2012)
• Annual events become daily events
• “100-year” event occurs several times per year
• Approximation: 0.1 m rise triples frequency of events
Key Conclusions
Victoria University of Wellington & GNS Science
• 3-5M years ago, 400ppm pCO2 caused ice sheet collapse and 10-20m sea level increase
• ~135k years ago, 280ppm pCO2 caused ice sheet collapse and 4-8 m sea level increase
• Projected sea level rise is up to 1m by 2100• BUT Paleo records suggests system is capable of
much higher rates of sea level rise (up to 4m/century)• We are at 400ppm pCO2 • Threshold and timing of West Antarctic Ice Sheet
collapse are yet to be determined