Waking Giants: Ice Sheets in a Warming World

Transcription

1 Waking Giants: Ice Sheets in a Warming World Dr. Robert Bindschadler Chief Scien6st Hydrospheric and Biospheric Sciences Laboratory NASA Goddard Space Flight Center Robert.A.Bindschadler@nasa.gov

2 Ice Sheets mager Globally Land area lost by 1 meter rise in sea level Source: CReSIS and NASA

3 Impact of 1 meter sea level rise: From Anthoff et al., 2006 Maldives

4 Sustained ice sheet observa6ons have captured a series of recent Surprises Ice shelf disintegra6ons Since mid 1980s Accelera6ng outlet glaciers Since mid 1990s Retrea6ng ice sheet margins Since 2000 Decreasing ice sheet volume Since mid 1990s Accelera6ng rates of change are no longer the excep6on are becoming the rule

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6 Accelera6ng Outlet Glaciers K 210% increase ( ) J H K Velocity (m/yr.) H J 60% increase ( ) 95% increase ( ) (Source: I. Joughin) (Rignot and Kanagaratnam, 2006)

7 Rapid Retreat in Greenland Jacobshavns Isbrae rs 5 yea rs a 40 ye Jacobshavns Isbrae

8 Ice Sheet Mass Balance Analyses (Source: Bell, 2008) Eleva6on change Mass change Velocity &Accumula6on Eleva6on change Velocity &Accumula6on (Sources: Zwally et al., 2006; and Rignot &Thomas, 2002)

9 Greenland Ice Sheet Mass Balance GREENLAND

10 Antarc6c Ice Sheet Mass Balance ANTARCTICA Ice sheets are changing fast

11 History Lesson Less ice in warmer climates Ice sheets shrink faster than they grow Sea level change is not smooth HIGH LOW THEN SEA LEVEL TEMPERATURE Time COLD Less ice More ice WARM NOW Ice sheet dynamics magers

12 IPCC Gold Standard in Climate Science Scien6sts work very hard to get this right Sea level predic6on (<0.59 m by 2100 in last report) is based on climate models without inclusion of rapid ice flow dynamics Larger values cannot be excluded understanding of these effects is too limited to assess their likelihood or provide a best es6mate or an upper bound for sea level rise.

13 Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond (a.k.a. NRC Decadal Survey) Key Ques6on #1 (of 6): Will there be catastrophic collapse of the major ice sheets, including Greenland and West Antarc6ca and, if so, how rapidly will this occur? What will be the 6me pagerns of sea level rise as a result?

14 Without good predic6ve ice sheet models Use: Extrapolate Direct Observa6ons Apply Proxy data sets Apply Analogues Do: Field work on the missing processes Improve models all as fast as possible

15 Extrapola6on 1. Observed glacier accelera6ons were applied to addi6onal glaciers 2. Addi6onal accelera6ons were applied to already fast moving glaciers Range of sea level by 2100: 0.8 to 2.0 m

16 Proxies 1. Rate of sea level rise empirically related to global temperature 2. Rela6onship applied to predicted future temperatures Range of sea level by 2100: 0.5 to 1.4 m

17 Analogues Muir Glacier, Alaska Tidewater glaciers are a good analogue to margins of modern ice sheets 1971

18 Tidewater glaciers exhibit dras6c retreat Helheim Glacier, Greenland Columbia Glacier, Alaska?? image (GoogleEarth) 1996 aerial photograph Source: USGS

19 Fingerprint of Collapse in Antarc6ca? Pine Island, Thwaites and Smith Glaciers exhibit expected signs of collapsing: Thinning rate Thinning increasing towards coast (satellite al6metry) Flow accelera6on (InSAR) Pine Island Gl. Thwaites Gl. Smith Gl. Retreat of grounding line (Landsat) Calving of large icebergs (MODIS) All observa6ons made by satellite sensors. Most of this area has never been visited by humans.

20 Central region of Greenland is below sea level Jacobshavns Isbrae occupies subglacial channel connected to central depression Russel Huff, Univ. of Colorado

21 Antarc6ca West Ant. East Ant. Nearly all of West Antarc6ca ice sheet and much of East Antarc6ca ice sheet rests on bed below sea level

22 Preview of next IPCC SeaRISE What s the worst it could be? Ice2Sea What s our best es6mate?

23 Summary Ice sheets are becoming more ac6ve in a warming world Less ice (and higher sea level) will be the result How much and how soon are uncertain 1 meter by 2100 is likely Won t be much beger and could be much worse Glaciologists are working in the field and on models to improve predic6ons of future ice sheet behavior

24 Thank you! Photo: I. Joughin Ques6ons?