NASA Finds Polar Ice Adding More to Rising Seas

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Alan Buis 818-354-0474
Jet Propulsion Laboratory, Pasadena, Calif.
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Janet Wilson 949-824-3969
University of California, Irvine
janethw@uci.edu

News release: 2011-070 March 8, 2011

NASA Finds Polar Ice Adding More to Rising Seas

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2011-070&cid=release_2011-070

PASADENA, Calif. -- The Greenland and Antarctic ice sheets are losing mass at an accelerating
pace, according to a new NASA-funded satellite study. The findings of the study -- the longest to
date of changes in polar ice sheet mass -- suggest these ice sheets are overtaking ice loss from Earth's
mountain glaciers and ice caps to become the dominant contributor to global sea level rise, much
sooner than model forecasts have predicted.

The nearly 20-year study reveals that in 2006, a year in which comparable results for mass loss in
mountain glaciers and ice caps are available from a separate study conducted using other methods, the
Greenland and Antarctic ice sheets lost a combined mass of 475 gigatonnes a year on average. That's
enough to raise global sea level by an average of 1.3 millimeters (.05 inches) a year. (A gigatonne is
one billion metric tons, or more than 2.2 trillion pounds.)

The pace at which the polar ice sheets are losing mass was found to be accelerating rapidly. Each year
over the course of the study, the two ice sheets lost a combined average of 36.3 gigatonnes more than
they did the year before. In comparison, the 2006 study of mountain glaciers and ice caps estimated
their loss at 402 gigatonnes a year on average, with a year-over-year acceleration rate three times
smaller than that of the ice sheets.

"That ice sheets will dominate future sea level rise is not surprising -- they hold a lot more ice mass
than mountain glaciers," said lead author Eric Rignot, jointly of NASA's Jet Propulsion Laboratory,
Pasadena, Calif., and the University of California, Irvine. "What is surprising is this increased
contribution by the ice sheets is already happening. If present trends continue, sea level is likely to be
significantly higher than levels projected by the United Nations Intergovernmental Panel on Climate
Change in 2007. Our study helps reduce uncertainties in near-term projections of sea level rise."

Rignot's team combined nearly two decades (1992-2009) of monthly satellite measurements with
advanced regional atmospheric climate model data to examine changes in ice sheet mass and trends in
acceleration of ice loss.

The study compared two independent measurement techniques. The first characterized the difference
between two sets of data: interferometric synthetic aperture radar data from European, Canadian and
Japanese satellites and radio echo soundings, which were used to measure ice exiting the ice sheets;
and regional atmospheric climate model data from Utrecht University, The Netherlands, used to
quantify ice being added to the ice sheets. The other technique used eight years of data from the
NASA/German Aerospace Center's Gravity Recovery and Climate Experiment (Grace) satellites,
which track minute changes in Earth's gravity field due to changes in Earth's mass distribution,
including ice movement.

The team reconciled the differences between techniques and found them to be in agreement, both for
total amount and rate of mass loss, over their data sets' eight-year overlapping period. This validated
the data sets, establishing a consistent record of ice mass changes since 1992.

The team found that for each year over the 18-year study, the Greenland ice sheet lost mass faster
than it did the year before, by an average of 21.9 gigatonnes a year. In Antarctica, the year-over-year
speedup in ice mass lost averaged 14.5 gigatonnes.

"These are two totally independent techniques, so it is a major achievement that the results agree so
well," said co-author Isabella Velicogna, also jointly with JPL and UC Irvine. "It demonstrates the
tremendous progress that's being made in estimating how much ice the ice sheets are gaining and
losing, and in analyzing Grace's time-variable gravity data."

The authors conclude that, if current ice sheet melting rates continue for the next four decades, their
cumulative loss could raise sea level by 15 centimeters (5.9 inches) by 2050. When this is added to the
predicted sea level contribution of 8 centimeters (3.1 inches) from glacial ice caps and 9 centimeters
(3.5 inches) from ocean thermal expansion, total sea level rise could reach 32 centimeters (12.6
inches). While this provides one indication of the potential contribution ice sheets could make to sea
level in the coming century, the authors caution that considerable uncertainties remain in estimating
future ice loss acceleration.

Study results are published this month in Geophysical Research Letters. Other participating
institutions include the Institute for Marine and Atmospheric Research, Utrecht University, The
Netherlands; and the National Center for Atmospheric Research, Boulder, Colo.

JPL developed Grace and manages the mission for NASA. The University of Texas Center for Space
Research in Austin has overall mission responsibility. GeoForschungsZentrum Potsdam (GFZ),
Potsdam, Germany, is responsible for German mission elements.

More on Grace is online at http://www.csr.utexas.edu/grace/ and http://grace.jpl.nasa.gov/ .

JPL is managed for NASA by the California Institute of Technology in Pasadena.

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