Scientific Basis

1. Scientific Basis The mission of CReSIS is to develop technologies; conduct field investigations; compile and analyze data to characterize ongoing rapid changes in polar ice sheets and to develop models that explain and predict ice-sheet interactions with climate and sea level.

2. Climate Change and Variability • If current climate projections are correct, then climate changes of the next ten to twenty years will significantly and noticeably impact human activities. This impact will shift research from climate change detection to research on the predictive capability necessary to protect life and property, promote economic vitality, enable environmental stewardship, and support a broad range of decision-makers. (NRC Decadal Survey, Climate Panel)

3. Climate Research 2005-2015 • Realization of future climate change forces our decadal vision to extend outside of the current state of the science in several ways: • Climate change research will be increasingly tied to improving predictive capabilities • The drive to create more comprehensive models will grow significantly • The “family” of forecasting products will grow substantially. • The tie between climate research and societal benefit will emphasize regional or higher spatial resolution climate prediction. • The connection between climate and specific impacts on natural and human systems will require a more comprehensive approach to environmental research.

4. Arctic Sea Ice Polar Regions and Global Climate • The polar regions and their icy cover are well documented indicators of climate change • High latitude processes are important drivers in climate change and sea level rise • Observations, modeling and prediction of high latitude processes must be a key element of our national climate research strategy • Remote sensing is an essential tool for exploring these most remote parts of our planet 0.8% decrease in Ice Shelf extent between 1963 and 1997

5. 30 km Ice Sheet/Ice Shelf ChangeAntarctica 1963 In last several years, we have witnessed numerous changes in the behavior of glaciers and ice sheets • Larsen ice shelf collapse • Antarctic Peninsula glacier acceleration post ice shelf collapse (Scambos, 2004) • Pine Island and Thwaites Glaciers Thinning (0.75-2.5 ma-1; Wingham) • GRACE 2002-2005: Ice sheet mass decrease at a rate of 152 ± 80 km3/year of ice, equivalent to 0.4 ± 0.2 mm/year of global sea level rise. 2000 2003

6. Ice Sheet Ice Shelf ChangesGreenland Outlet Glacier Acceleration • Rapid thinning of Jacobshavn Glacier, Greenland (> 10 m a-1, Thomas, 2003) • Glacier acceleration and increased mass deficit about Greenland periphery (Rignot and Kanagaratnam, 2006) loss of 224 +/- 41 km3 ice/year in 2005 • But, Zwally (2006) suggests Greenland actually gaining mass (-0.03 mma-1 sea level rise) (?) m/yr Observed rapid changes in Greenland and Antarctica are not predicted by climate models (slow and linear response to climate forcing; fast glacier flow not included)

7. Glaciers and Ice Sheets ‘Grand Challenges’ • Understand the polar ice sheets sufficiently to predict their response to global climate change and their contribution global sea level rise • What is the mass balance of the polar ice sheets? • What causes abrupt changes in ice sheet motion? • How will the mass balance change in the future? 1962-2005 148 sq km loss Speed doubling 2005

8. Mass Balance • Ice sheet mass balance is described by the mass continuity equation Altimeters Act/Pass. Microwave Airborne wideband InSAR (assumes U constant with depth) Airborne Radar Seismics Evaluations of the left and right hand sides of the equation will yield a far more complete result

9. Airborne Radar Satellite Altimetry Basal Drag, Inferred at best Ice Dynamics and Prediction Force Balance Equations Terms related to gradients in ice velocity (InSAR) integrated over thickness Understanding dynamics coupled with the continuity equations yields predictions on future changes in mass balance

10. CReSIS Science Objectives 3. Characterize ongoing rapid changes in polar ice sheets 4. Improve existing theories for describing the onset and triggers of fast glacier flow; 5. Extend theories for describing calving mechanisms and ice margin retreat; 6. Better understand of how ice shelves and ice tongues modulate upstream flow; 7. Predict where and at what rate ice sheets will likely change in the coming decades; 8. Facilitate linkages between CReSIS process studies and community global circulation models. 1. Conduct basic exploration of those parts of our planet that are hidden by thick polar ice; 2. Improve 3-dimensional measurements of ice sheet physical properties, especially ice sheet hydrology;

11. Ideas and Hypotheses to Guide CReSIS • Recent Ideas in Glacier Mechanics • 1)  Role and evolution of side drag to basal drag on ice streams (Van der Veen and Whillans).   Predicts the width of the melt zone and the longitundinal extent underneath the shear margin.  Rapid Thinning of Jacobshavn Glacier • 2)  Force perturbation theory that predicts longitudinal stresses in wide/thick glaciers that are changing. (Thomas)

12. Ideas and Hypotheses 3) Calving dynamics (polar vs tide water glaciological theory).  What mechanisms are causing the calving rate acceleration in Jacobshavn?  Can we extend MacAyeals model on water filled crevasses? Is it applicable?  4)  Investigate time dependencies by relaxing quasi-equilibrium force balance theory

13. Ideas and Hypotheses • Advanced material properties: • Ice jamming and granular materials theory (Johnson and Hughes) • Porosity, permeability and deformation properties of subglacial till and distribution of subglacial water • Goldsby Kohlstedt vs Glen’s flow law • Improved firn densification models coupled to radar scattering models • Analysis Methods • MacAyeal's control theory method.  Does the derived basal drag look like the distribution of water at the bed? • Bayesian inversion of the surface fields to get basal drag. 

14. Some Near Term Plans to Further Refine Our Thinking • CReSIS Overview Article To EOS • Tutorial on Microwave Remote Sensing of Ice Sheets (TGARSS) • Synopsis of latest glaciological theory (Polar Geography)