Transcript CReSIS Science Overview - Byrd Polar and Climate Research Center

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.
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
Advance (51,772.2 km2)
Retreat (100,099.6 km2)
Ice shelves
Area without ice shelves
0.8% decrease in Ice Shelf extent
between 1963 and 1997
Ice Sheet/Ice Shelf Change
Antarctica
30 km
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
Ice Sheet Ice Shelf Changes
Greenland
– 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) (?)
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/yr
Outlet Glacier Acceleration
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
1962-2005
148 sq km loss
Speed doubling
2005
•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?
Mass Balance
• Ice sheet mass balance is described
by the mass continuity equation
Altimeters
Act/Pass. Microwave
Airborne wideband
Airborne Radar
Seismics
InSAR
(assumes U constant with
depth)
Evaluations of the left and right hand sides of the
equation will yield a far more complete result
Ice Dynamics and
Prediction
Force Balance Equations
Airborne Radar
Satellite Altimetry
Basal Drag,
Inferred at best
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
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.
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)
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
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)