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 Arctic System Modeling Workshop UQAM, Montreal July 17, 2009

A Story of Two Ice Sheets Greenland Ice Sheet: Long, narrow Fjords Antarctic Ice Sheet: Wide expansive, ice shelves; West Antarctica marine based

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

- Jakobshavn Isbrae retreats in Forced by the ocean - (which was forced by the Atmosphere, the NAO) Recent Changes: Greenland

- Larsen B collapses in Forced by the surface melt ponds - (which was forced by the Atmosphere) Recent Changes: Antarctica

- Pine Island thinning over last decade - Forced by the ocean warm waters - (which was forced by the Atmosphere) Recent Changes: Antarctica

IPCC: Summary for Policy Makers

IPCC: “Excluding future rapid…”

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

Is it Predictable? Chaotic system? Rate of Observational Progress? Rate of Modeling Progress?

Russell et al, 2006 IPCC: Antarctic Circumpolar Current (an analog for uncertainty?)

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.

Challenges of Physics 1)physics of calving at ice fronts, 2)grounding line migration, 3)buttressing effects associated with ice geometry, 4)basal melting of ice-shelves, and the associated sub-ice-shelf ocean circulation.

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

Challenges of Computation 1)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. 2)within the ice models themselves how to represent regions of rapid dynamic changes, such as at the grounding line.

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

Ice Sheet Modeling Community West Antarctic Ice Sheet Initiative (WAIS)

Ice Sheet Modeling Community Forum for Research Into Ice Shelf Processes (FRISP)

Ice Sheet Modeling Community Ice Sheet Model Intercomparison Project (ISMIP)

Recent “Sea-Level” Workshops Evolution of the Antarctic Ice Sheet Royal Society of London, 2005

Recent “Sea-Level” Workshops Understanding Sea-Level Rise and Variability Paris, 2006

Recent “Sea-Level” Workshops Toward a New Generation of Ice Sheet Models GFDL, 2007

Predicting Sea Level in the 21 st Century: The Role of Ice-Ocean Interaction New York University, 2008 Recent “Sea-Level” Workshops … to stimulate activity between the cryospheric community and climate modelers in national laboratories …

Recent “Sea-Level” Workshops Workshop on Improving Ice Sheet Models SCAR, 2008

Recent “Sea-Level” Workshops Building a Next Generation Community Ice Model LANL, 2008

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

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)

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

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

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)

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