The East Antarctic icesheet, once seen as largely
unaffected by global warming, has lost billions of tonnes of ice since
2006 and could boost sea levels in the future, according to a new study.
Sunday in Nature Geoscience, the same study shows that the smaller but
less stable West Antarctic icesheet is also shedding significant mass.
worry that rising global temperatures could trigger a rapid
disintegration of West Antarctica, which holds enough frozen water to
push up the global ocean watermark by about five metres (16 feet).
In 2007 the UN Intergovernmental Panel for Climate
Change (IPCC) predicted sea levels would rise 18 to 59 centimetres (7.2
to 23.2 inches) by 2100, but this estimate did not factor in the
potential impact of crumbling icesheets in Greenland and Antarctica.
many of the same scientist say that even if heat-trapping CO2 emissions
are curtailed, the ocean watermark is more likely to go up by nearly a
metre, enough to render several small island nations unlivable and
damage fertile deltas home to hundreds of millions.
than 190 nations gather in Copenhagen next month to hammer out a global
climate deal to curb greenhouse gases and help poor countries cope with
University of Texas professor
Jianli Chen and colleagues analysed nearly seven years of data on
ocean-icesheet interaction in Antarctica.
the period up January 2009, the data was collected by the twin GRACE
satellites, which detect mass flows in the ocean and polar regions by
measuring changes in Earth's gravity field.
with earlier findings based on different methods, they found that West
Antarctica dumped, on average, about 132 billion tonnes of ice into the
sea each year, give or take 26 billion tonnes.
also found for the first time that East Antarctica - on the Eastern
Hemisphere side of the continent - is likewise losing mass, mostly in
coastal regions, at a rate of about 57 billion tonnes annually.
margin or error, they cautioned, is almost as large as the estimate,
meaning ice loss could be a little as a few billion tonnes or more than
Up to now, scientists had thought that
East Antarctica was in "balance," meaning that it accumulated as much
mass and it gave off, perhaps a bit more.
of ice loss in recent years over the entire continent is thus
indicated," the authors conclude. "Antarctica may soon be contributing
significantly more to global sea level rise."
study published last week in the journal Nature reported an
upwardly-revised figure for Antarctic temperatures during prior
"interglacials", warm periods such as our own that have occurred
roughly every 100,000 years.
During the last
interglacial which peaked some 128,000 years ago, called the Eemian
Period, temperatures in the region were probably six degree Celsius
(10.8 degrees Fahrenheit) higher than today, which is about 3 C (5.4 C)
above previous estimates, the study said.
findings suggest that the region may be more sensitive than scientists
thought to greenhouse gas concentrations in the atmosphere that were
roughly equivalent to present day levels.
During the Eemian, sea levels were five-to-seven metres higher than today.