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
Polar Regions and Global Climate
Arctic Sea Ice

• 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
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
  (gt 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
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
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CReSIS Science Objectives
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

• 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.

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 Glens 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)