March
28, 2007 THINNING
OF WEST ANTARCTIC ICE SHEET DEMANDS IMPROVED MONITORING TO REDUCE
UNCERTAINTY
OVER POTENTIAL SEA-LEVEL RISE Polar ice experts
from Europe and the United
States, meeting to pursue greater scientific consensus over the fate of
the
world’s largest fresh water reservoir, the West Antarctic Ice
Sheet, conclude
their three-day meeting at The University of Texas at
Austin’s Jackson School
of Geosciences with the following statement: -Satellite
observations show that
both the grounded ice sheet and the floating ice shelves of the
Amundsen Sea
Embayment have thinned over the last decades. -Ongoing thinning in
the grounded
ice sheet is already contributing to sea-level rise. -The thinning of the
ice has
occurred because melting beneath the ice shelves has increased,
reducing the
friction holding back the grounded ice sheet and causing faster flow. -Oceanic changes
have caused the
increased ice-shelf melting. The observed average warming of the global
ocean
has not yet notably affected the waters reaching the base of the ice
shelves.
However, recent changes in winds around -Our understanding
of ice-sheet
flow suggests the possibility that too much melting beneath ice shelves
will
lead to “runaway” thinning of the grounded ice
sheet. Current understanding is
too limited to know whether, when, or how rapidly this might happen,
but
discussions at the meeting included the possibility of several feet of
sea-level rise over a few centuries from changes in this region. -The experts agreed
that to reduce
the very large uncertainties concerning the behavior of the Antarctic
ice in
the Amundsen Sea Embayment will require new satellite, ground, and
ship-based
observations coupled to improved models of the ice-ocean-atmosphere
system.
Issues include: --The recent changes
were
discovered by satellite observations; however, continued monitoring of
some of
these changes is not possible because of a loss of capability in
current and
funded satellite missions. --The remoteness of
this part of --No oceanographic
observations
exist beneath the ice shelves, and other oceanographic sampling is too
infrequent and sparse to constrain critical processes. --Current
continental-scale ice
sheet models are inadequate for predicting future sea level rise
because they
omit important physical processes. --Current global
climate models do
not provide information essential for predicting ice sheet and oceanic
changes
in the Amundsen Sea Embayment; for example, ice shelves are not
included. Resolving these
issues will substantially improve
our ability to predict the future sea level contribution from the
Amundsen Sea
Embayment of the Antarctic Ice Sheet.
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