Report on Ice Sheet Modelling Activities

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Report on Ice Sheet Modelling Activities

• David Holland
• Courant Institute of Mathematical Sciences
• New York University, NY USA
•  
• Jonathan Gregory
• Walker Institute, Department of Meteorology,
  University of Reading, UK
• Met Office Hadley Centre, Exeter, UK

WCRP/CLIVAR Working Group on Coupled Modelling
12th Session Paris, France September 20, 2008
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A Story of Two Ice Sheets
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• Why does it matter?
• What are the obstacles to progress?
• What are we doing?

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Recent Changes Greenland

• - Jakobshavn Isbrae retreats in 1997
• Forced by the ocean
• (which was forced by the Atmosphere, the NAO)

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Recent Changes Antarctica

• - Larsen B collapses in 2002
• Forced by the surface melt ponds
• (which was forced by the Atmosphere)

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Recent Changes Antarctica

• - Pine Island thinning over last decade
• Forced by the ocean warm waters
• (which was forced by the Atmosphere)

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IPCC Summary for Policy Makers
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IPCC Excluding future rapid
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• Why does it matter?
• What are the obstacles to progress?
• What are we doing?

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Is it Predictable?
Chaotic system? Rate of Observational
Progress? Rate of Modeling Progress?
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IPCC Antarctic Circumpolar Current (an analog
for uncertainty?)
Russell et al, 2006
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Challenges of Physics
there remains uncertainty in the physics that
controls the rate of flow of ice steams coming
from the land and feeding into the ice shelves,
floating on the ocean.
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Challenges of Physics

• physics of calving at ice fronts,
• grounding line migration,
• buttressing effects associated with ice geometry,
• basal melting of ice-shelves,
• and the associated sub-ice-shelf ocean
  circulation.

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Challenges of Physics
even regarding the comparatively
well-understood processes determining ice-sheet
surface mass balance, there are substantial
uncertainties.
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Challenges of Computation

• how to represent on the grids of relatively
  coarse resolution global climate models the steep
  marginal areas of ice-sheets, on which any
  surface melting occurs, and the coastal ocean
  circulation that may impinge on ice-shelves.
• within the ice models themselves how to represent
  regions of rapid dynamic changes, such as at the
  grounding line.

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• Why does it matter?
• What are the obstacles to progress?
• What are we doing?

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Ice Sheet Modeling Community
West Antarctic Ice Sheet Initiative (WAIS)
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Ice Sheet Modeling Community
Forum for Research Into Ice Shelf Processes
(FRISP)
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Ice Sheet Modeling Community
Ice Sheet Model Intercomparison Project (ISMIP)
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Recent Sea-Level Workshops
Evolution of the Antarctic Ice Sheet Royal
Society of London, 2005
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Recent Sea-Level Workshops
Understanding Sea-Level Rise and
Variability Paris, 2006
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Recent Sea-Level Workshops
Toward a New Generation of Ice Sheet Models GFDL,
2007
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Recent Sea-Level Workshops
to stimulate activity between
the cryospheric community and climate
modelers in national laboratories
Predicting Sea Level in the 21st Century The
Role of Ice-Ocean Interaction New York
University, 2008
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Recent Sea-Level Workshops
Workshop on Improving Ice Sheet Models SCAR, 2008
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Recent Sea-Level Workshops
Building a Next Generation Community Ice
Model LANL, 2008
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UK Efforts

• Hadley Centre using HadCM3 coupled to the
  Greenland 3D ISM of Huybrechts
• starting to use the Glimmer 3D ISM coupled to
  Hadley Centre AOGCMs
• Glimmer is being developed (led by Payne), to
  include an adaptive-mesh high-resolution
  treatment of ice streams and the grounding line
• The Hadley Centre AGCM is being improved as
  regards ice-sheet surface mass balance

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EU Effort ice2sea

• proposed EU Framework 7 project on estimating
  the future contribution of continental ice to
  sea-level rise
• focus on key processes not included in current
  models,
• essential observations (especially for the
  satellite period),
• projection of ice-sheet surface mass balance and
  ice-shelf basal mass balance using regional
  atmosphere and ocean models,
• projection of ice-sheet response over 200 years,
  
• and synthesis including regional sea-level
  projection
• and risk assessment
• does not include model development, two-way
  coupling between ice sheet and climate (only
  climate-ice-sheet)

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LANL Efforts

• developing a Community Ice Sheet Model (CISM)
• implementing CISM in the
• Community Climate System Model (CCSM)
• strategy for developing an IPCC-ready community
  ice sheet model in 1 to 2 years
• and fully coupled model later on

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Conclusions The Good

• there exists an ever-growing (?) and diverse
  group of researchers studying ice sheets and sea
  level
• some detectable momentum in EU and USA efforts

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Conclusions The Bad

• Topography poorly known
• Hydrographic Observations in the cavity are
  inadequate
• Models are poorly constrained
• Parameterizations of melting are inaccurate by
  at least 100
• Most 3-D models have static ice shelf and
  dynamic ocean (or vice versa)

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Conclusions The Ugly

• No existing capability to model future
• sea level change
• The capability is not obviously going to emerge
  anytime soon
• There is no detailed plan