From: Andy Soos, ENN
Published November 29, 2012 10:28 AM
Antarctic Melting and Sea Level
Due to its location at the South Pole, Antarctica receives relatively
little solar radiation. This means that it is a very cold continent
where water is mostly in the form of ice or snow. This accumulates and
forms a giant ice sheet which covers the land. New data which more
accurately measures the rate of ice-melt could help us better understand
how Antarctica is changing in the light of global warming. The rate of
global sea level change is reasonably well-established but understanding
the different sources of this rise is more challenging. Using
re-calibrated scales that are able to weigh ice sheets from space to a
greater degree of accuracy than ever before, the international team led
by Newcastle University has discovered that Antarctica overall is
contributing much less to the substantial sea-level rise than originally
thought.
Instead, the large amount of water flowing away from West Antarctica
through ice-melt has been partly cancelled out by the volume of water
falling onto the continent in the form of snow, suggesting some past
studies have overestimated Antarctica’s contribution to fast-rising sea
levels.
Using Gravity Recovery and Climate Experiment (GRACE) satellite data,
the team calculated ice sheet mass loss by more accurately mapping and
removing the mass changes caused by the flow of rock beneath Earth’s
surface.
Publishing their findings in the academic journal Nature, project lead
Professor Matt King said the data meant we were at last close to
understanding how Antarctica is changing.
"We have tried to weigh the ice in the past but GRACE only measures the
combined effect of the ice changes and the land mass changes occurring
beneath the Earth’s surface," explains Professor King, Professor of
Polar Geodesy at Newcastle University. "The step forward we have made is
to provide a better calculation of the land mass changes so we can
correct the satellite measurements to more accurately calculate the
changes in ice mass alone."
"Our ice change calculations rely heavily on how well we can account for
these important changes taking place beneath the Earth’s surface. While
the land beneath the ice is moving by no more than a few
millimetres-per-year — the thickness of a fingernail —that seemingly
small effect significantly alters the rate at which we estimate the ice
is changing."
"By producing a new estimate of the land motion we’re effectively
re-calibrating the scales — in this case the GRACE satellite —so we can
more accurately weigh the ice. And what we’ve found is that present sea
level rise is happening with apparently very little contribution from
Antarctica as a whole."
"We’re now confident it is shrinking," says Professor King. "Our new
estimate of land motion helps us narrow the range and shifts the best
estimate to the lower end of the ice melt spectrum."
"Worryingly, though, the rate of shrinking has sped up in some important
locations. The parts of Antarctica that are losing mass most rapidly are
seeing accelerated mass loss and this acceleration could continue well
into the future."
"The sea level change we’re seeing today is happening faster than it has
for centuries with just a small contribution from the massive Antarctic
ice sheet. What is sobering is that sea levels will rise even faster if
Antarctica continues to lose increasingly more ice into the oceans."
Sea levels around the world are rising. Between 1870 and 2004, global
average sea levels rose 17 cm as reported in 2006 in Geophysical
Research Letters. From 1950 to 2009, satellite data showed a rise of
3.3 ± 0.4 mm from 1993 to 2009. In 2007, the Intergovernmental Panel on
Climate Change (IPCC) projected that during the 21st century, sea level
will rise another 18 to 59 cm (7.1 to 23 in).
Ice sitting on the Antarctic continent at the peak of the last ice age
20,000 years ago forced the rock beneath to deform and slowly flow away.
After that time ice levels generally reduced and the rock within the
Earth's mantle more than 100km below the surface has been slowly flowing
back in. That change affects the GRACE satellites in exactly the same
way as ice moving into and out of the continent and it has to be
factored in to get an accurate measurement of the total ice.
For further information see
Sea Levels.
Antarctica image via Wikipedia.
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