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.

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)

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.

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

Advance (51,772.2 km2) Retreat (100,099.6 km2) Ice shelves Area without ice shelves

0.8% decrease in Ice Shelf extentbetween 1963 and 1997

Arctic Sea Ice

Ice Sheet/Ice Shelf ChangeAntarctica

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.

30 km

1963

2000

2003

Ice Sheet Ice Shelf ChangesGreenland

– 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) (?)

Outlet Glacier Acceleration

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)

m/y

r

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?

2005

1962-2005148 sq km lossSpeed doubling

Mass Balance• Ice sheet mass balance is described

by the mass continuity equation

Altimeters

InSAR(assumes U constant with

depth)

Act/Pass. MicrowaveAirborne wideband

Airborne RadarSeismics

Evaluations of the left and right hand sides of the equation will yield a far more complete result

Ice Dynamics and Prediction

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

Force Balance Equations

Basal Drag,Inferred at best

Satellite AltimetryAirborne Radar

CReSIS Science Objectives

3. Characterize ongoing rapid changes in polar ice sheets4. 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;

Ideas and Hypotheses to Guide CReSIS

• Recent Ideas in Glacier Mechanics

Rapid Thinning of Jacobshavn Glacier

2)  Force perturbation theory that predicts longitudinal stresses in wide/thick glaciers that are changing. (Thomas)

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. 

Ideas and Hypotheses3) 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

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. 

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)