Ice sheets in Glacier Bay National Park are subject to dynamics that SEACISM researchers simulate on leadership-class supercomputers. Credit: Kate Evans |
Recently, Rhode Island-sized chunks of ice
have separated from Greenland and Antarctica,
garnering worldwide attention. But is this calving due to typical seasonal
variations or a long-term warmer world? Climate scientists already use ice
sheet models to better understand how ice loss affects sea levels; however,
those models are not easily adapted for use in global climate models. In August
the Scalable, Efficient, and Accurate Community Ice Sheet Model project began
on Jaguar at Oak Ridge National Laboratory. SEACISM’s aim is to use simulation
to predict the behavior of ice sheets under a changing climate by developing
scalable algorithms.
“Right now we don’t know enough to
predict the dynamics of the ice sheets,” said ORNL computational Earth
scientist Kate Evans, who leads the SEACISM project. Included in the team are
other scientists from ORNL, Los Alamos National Laboratory, Sandia National
Laboratories, New York
Univ., and Florida State
Univ. Their goal is to address this lack of understanding by reducing
uncertainties about climate and sea-level predictions through high-fidelity
simulations that resolve important ice sheet features.
The Fourth Assessment Report of the
Intergovernmental Panel on Climate Change did not provide a prediction of ice
sheet fate due to a lack of data. Given the importance of building a predictive
capability, the Department of Energy’s Office of Advanced Scientific Computing
Research created an initiative to meet that need. ASCR’s Scientific Discovery
through Advanced Computing program funded the Ice Sheet Initiative for CLimate
ExtremeS to yield high-fidelity, high-resolution ice sheet models.
SEACISM is one of six projects launched from
ISICLES, all of which respond to the national and international need to include
better ice sheet dynamic simulations in Earth system models. Among other
objectives, the projects will quantify uncertainties of dynamic predictions and
develop models to efficiently use supercomputers. ASCR’s Leadership Computing
Challenge program granted SEACISM researchers 5 million processor hours on
Jaguar, a leadership computing facility system capable of up to 2.3 quadrillion
calculations per second. Another 1 million hours for SEACISM were allocated on
Argonne National Laboratory’s LCF supercomputer Intrepid, with a peak speed of
557 trillion calculations per second.
The scientists working on SEACISM are
collaborating to extend Glimmer-CISM, a three-dimensional thermomechanical ice
sheet model that has recently been incorporated into the Community Earth System
Model. CESM is a coupled global climate model comprised of atmosphere,
land-surface, ocean, and sea-ice model components. SEACISM researchers are
using the hours allocated in 2010 to prepare for the inclusion of the ice sheet
model in simulations run as part of the Climate-Science End Station, an
Innovative and Novel Computational Impact on Theory and Experiment, or INCITE,
project that runs on the LCF systems.
“We need SEACISM to be working
efficiently on LCF systems by next year,” Evans said. The team is running
test cases to validate newly developed model features. Once the code reproduces
previous results, the team will move on to cases of increasing size and
complexity. More detailed equations and finer grids build more complexity into
the model, which allows better resolution of features such as the grounding
line, a crucial juncture at which the floating ice shelf meets the land surface
below it.
The SEACISM team is working on
several journal articles about its research and will present intermediate
results to the CESM’s Land Ice Working Group in Boulder, Colo.,
in January. It hopes the model improvements will allow climate scientists to
provide simulation data about ice sheet dynamics that will inform the next IPCC
assessment report, expected in 2013.
