potential collapse of the west antarctic ice sheet...

Potential collapse of the West Antarctic Ice Sheet – Implications for global sea level rise

Nancy Bertler

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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?

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IPCC Projections for 2100 AD

IPCC, AR5, WG1,Figure SPM 8

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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

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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


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)


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


Today

Then

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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


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)


Evidence of Antarctic Change – Warming Surface Temperature

Steig et al., Jan 2009, Nature


Böning et al., Dec 2008, Nature

Evidence of Antarctic Change – Warmer Ocean


• 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


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


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


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Data constraints – Agreement between different methods

Sutterley et al. 2014, GRL

• Good agreement• Acceleration by

16.3 Gt/yr2 (3x)


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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


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


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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


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)


Regional Pattern in Sea Level?


(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


Changes in Occurrence Coastal Inundation for RCP 4.5


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


• 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

potential collapse of the west antarctic ice sheet...

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