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Antarctic Ice Sheet Losing Mass

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  • Pat Neuman
    http://www.terradaily.com/reports/Antarctic_Ice_Sheet_Losing_Mass.htm l Antarctic Ice Sheet Losing Mass by Staff Writers Boulder CO (SPX) Mar 03, 2006
    Message 1 of 1 , Mar 2, 2006

      Antarctic Ice Sheet Losing Mass

      by Staff Writers
      Boulder CO (SPX) Mar 03, 2006
      University of Colorado at Boulder researchers have used data from a
      pair of NASA satellites orbiting Earth in tandem to determine that
      the Antarctic ice sheet, which harbors 90 percent of Earth's ice,
      has lost significant mass in recent years.
      The team used measurements taken with the Gravity Recovery and
      Climate Experiment, or GRACE, to conclude the Antarctic ice sheet is
      losing up to 36 cubic miles of ice, or 152 cubic kilometers,
      annually. By comparison, the city of Los Angeles uses about 1 cubic
      mile of fresh water annually.

      "This is the first study to indicate the total mass balance of the
      Antarctic ice sheet is in significant decline," said Isabella
      Velicogna of CU-Boulder's Cooperative Institute for Research in
      Environmental Sciences, chief author of the new study that appears
      in the March 2 online issue of Science Express. The study was co-
      authored by CU-Boulder physics Professor John Wahr of CIRES, a joint
      campus institute of CU-Boulder and the National Oceanic and
      Atmospheric Administration.

      The estimated ice mass in Antarctica is equivalent to 0.4
      millimeters of global sea rise annually, with a margin of error of
      0.2 millimeters, according to the study. There are about 25
      millimeters in an inch.

      The most recent Intergovernmental Panel on Climate Change
      assessment, completed in 2001, predicted the Antarctic ice sheet
      would gain mass in the 21st century due to increased precipitation
      in a warming climate. But the new study signals a reduction in the
      continent's total ice mass, with the bulk of loss occurring in the
      West Antarctic ice sheet, said Velicogna.

      Researchers used GRACE data to calculate the total ice mass in
      Antarctica between April 2002 and August 2005 for the study, said
      Velicogna, who also is affiliated with the NASA's Jet Propulsion
      Laboratory in Pasadena.

      "The overall balance of the Antarctic ice is dependent on regional
      changes in the interior and those in the coastal areas," said
      Velicogna. "The changes we are seeing are probably a good indicator
      of the changing climatic conditions there."

      Launched in 2002 by NASA and Germany, the two GRACE satellites whip
      around Earth 16 times a day at an altitude of 310 miles, sensing
      subtle variations in Earth's mass and gravitational pull. Separated
      by 137 miles at all times, the satellites measure changes in Earth's
      gravity field caused by regional changes in the planet's mass,
      including such things as ice sheets, oceans and water stored in the
      soil and in underground aquifers.

      A change in gravity due to a pass over a portion of the Antarctic
      ice sheet, for example, imperceptibly tugs the lead satellite away
      from the trailing satellite, said Velicogna. A sensitive ranging
      system allows researchers to measure the distance of the two
      satellites down to as small as 1 micron -- about 1/50 the width of a
      human hair -- and to then calculate the ice mass in particular
      regions of the continent.

      "The strength of GRACE is that we were able to assess the entire
      Antarctic region in one fell swoop to determine whether it was
      gaining or losing mass," said Wahr. While the CU researchers were
      able to differentiate between the East Antarctic ice sheet and West
      Antarctic ice sheet with GRACE, smaller, subtler changes occurring
      in coastal areas and even on individual glaciers are better measured
      with instruments like radar and altimeters, he said.

      A study spearheaded by CIRES researchers at CU-Boulder and published
      in September 2004 concluded that glaciers on the Antarctic
      Peninsula - which juts north from the West Antarctic ice sheet
      toward South America -- sped up dramatically following the collapse
      of Larsen B ice shelf in 2002. Ice shelves on the peninsula -- which
      has warmed by an average of 4.5 degrees Fahrenheit in the past 60
      years -- have decreased by more than 5,200 square miles in the past
      three decades.

      As Earth's fifth largest continent, Antarctica is twice as large as
      Australia and contains 70 percent of Earth's fresh water resources.
      The ice sheet, which covers about 98 percent of the continent, has
      an average thickness of about 6,500 feet. Floating ice shelves
      constitute about 11 percent of the continent.

      The melting of the West Antarctic ice sheet alone - which is about
      eight times smaller in volume than the East Antarctic ice sheet --
      would raise global sea levels by more than 20 feet, according to
      researchers from the British Antarctic Survey.

      A floating iceberg off the Antarctic Peninsula. Photo courtesy CU-
      Boulder National Snow and Ice Data Center.

      Related Links
      University of Colorado at Boulder
      CU-Boulder's Cooperative Institute for Research in Environmental

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