Sea level contribution of Antarctica & Greenland Andrew Shepherd

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1 Andrew Shepherd School of Geosciences, Edinburgh

2 Sea Subglacial level contribution lakes of Antarctica & Greenland

3 Climate change Satellite observations Ice Sheets and Sea level

4 Climate change

5 Climate Change Slow climate change Mt Kilimanjaro, 1993

6 Climate Change Slow climate change Mt Kilimanjaro, 2000

7 Climate Change Abrupt climate change

8 Climate Change Abrupt climate change Larsen Ice Shelf, 2002

9 Abrupt climate change Larsen Ice Shelf, 2002

10 Abrupt climate change Larsen embayment, 2005

11 Climate Change Abrupt climate change Larsen sea bed, 2005 Domack et al., 2005

12 Climate Change IPCC Assessment reports (1990, 1995, 2001) 0.6 C rise since 1900 Global warming IPCC, 2001

13 Climate Change IPCC Assessment reports (1990, 1995, 2001) 15 cm rise since 1900 Global sea level rise IPCC, 2001

14 IPCC Measured sea level Thermal expansion Glaciers & ice caps Greenland Antarctica

15 IPCC 2007

16 IPCC 2007

17 IPCC 2007 (i) Models used to date do not include the full effects of changes in ice sheet flow, because a basis in published literature is lacking. (ii) Dynamical processes related to ice flow suggested by recent observations could increase the vulnerability of the ice sheets to warming, increasing future sea level rise. (iii) Understanding of these processes is limited and there is no consensus on their magnitude.

18 Zwally effect

19 Payne effect

20 Climate Change UK today

21 Climate Change UK today No Polar Ice Sheets

22 Satellite observations

23 Sea Polar level ice sheets contribution and sea of level Antarctica rise & Greenland Altimetry Interferometry Gravimetry

24 Altimetry

25 Altimetry Mass change from volume change

26 Gravimetry

27 Gravimetry Mass change from orbit change

28 Interferometry

29 Interferometry

30 Interferometry Mass change from glacier flow

31 Sea level contribution

32 Sea level Range of -366 to 53 Gt yr -1 equals 1.0 to mm yr -1 sea level contribution Factor 3 poorer certainty than last two IPCC reports

33 Sea level All methods are all sensitive to snowfall: Interferometry compares snowfall to, runoff &ice discharge Altimetry requires knowledge of density, which ranges from 350 to 900 kg m -3 Gravimetry measures change in snow and ice mass, and suffers from short time period (<3 years)

34 Sea level All methods are all sensitive to snowfall: Interferometry compares snowfall to, runoff &ice discharge Altimetry requires knowledge of density, which ranges from 350 to 900 kg m -3 Gravimetry measures change in snow and ice mass, and suffers from short time period (<3 years) Ice cores show 15 % fluctuations in MAR over short time periods Antarctica MAR = 6 mm esl Greenland MAR = 0.5 mm esl

35 Greenland

36 Greenland EAIS = Gt yr -1 (+0.3 mm yr -1 ) Altimetry misses coast Gravimetry studies do not concur InSAR shows acceleration

37 Greenland InSAR shows large and rapid fluctuations in Greenland glacier discharge Complicates estimates of decadal imbalance Recent (2007) decelleration shows signal to be non-secular

38 Greenland InSAR shows large and rapid fluctuations in Greenland glacier discharge Complicates estimates of decadal imbalance Recent (2007) decelleration shows signal to be nonsecular

39 Antarctica

40 Antarctica EAIS = + 25 Gt yr -1 (-0.07 mm yr -1 ) WAIS = - 50 Gt yr -1 (+0.14 mm yr -1 ) Altimetry & interferometry concur Gravimetry overestimates loss (-150 Gt yr -1 ), because of recent snowfall shortfall (100 Gt yr -1 )

41 Antarctica

42 Antarctica PIG thinning due to <0.5 C ocean warming Has triggered 50 Gt yr -1 ice loss from 2 glaciers (0.14 mm yr -1 ) 21 st C warming up to 4 C

43 Summary Recent sea level contribution of Antarctica and Greenland is 0.35 mm yr -1 Half of this is due to recent acceleration of Greenland, which has since abated Only submarine-based & coastal Antarctic glaciers show secular trend Evolution of these glaciers poses immediate threat to future sea levels