The New Scientist March 11,
2011
http://www.newscientist.com/article/dn20233-sea-levels-rise-
and-rise-is-down-to-melting-ice-sheets.html
Sea level's
rise and rise is down to melting
ice sheets
By Anil
Ananthaswamy
Greenland
and Antarctica are losing ice at
a faster and faster rate,
according
to a new study that has tracked
the rate of melting in two
independent
ways. At this rate, melting ice
sheets could dominate sea
level rise
in the 21st century.
The most
recent report by the
Intergovernmental Panel on
Climate
Change
suggested that sea levels could
rise by 18 centimetres to 59
cm by
2100Speaker - but that estimate
didn't take the Greenland and
Antarctic
ice sheets into
account.
The new
study, by Eric Rignot of the
University of California,
Irvine, and
colleagues, could make things
clearer. The team studied
changes in
the two ice sheets between 2002
and 2010 using two
techniques.
First they used data from the
NASA GRACE satellite, which
directly
estimates the changes in the ice
mass by measuring Earth's
gravity
field over Greenland and
Antarctica. The gravity field is
influenced
by changes in ice
mass.
Next, they
used a mass balance approach,
which involves taking
monthly
measurements of glacier movement
and ice thickness and
plugging
them into a regional climate
model to estimate the net
accumulation
of snow and ice.
Fast ice
loss
Both
techniques broadly agreed on the
quantity of ice being lost.
They both
confirmed, for example, that in
2006 the ice sheets of
Greenland
and Antarctica together lost a
total of 475 gigatonnes. The
two data
sets also agree that the rate of
mass loss from the ice
sheets is
increasing at about 36 gigatonnes
per year - three times
faster than
the rate of mass loss from
mountain glaciers and ice
caps.
Because the
two data sets agree both methods
are validated.
Measurements
were taken using the mass balance
approach for several
years
before the launch of GRACE in
2002, and indicate that melting
has been on
the increase for at least two
decades.
"The mass
loss is accelerating and it
appears to have been
accelerating
for a while," says Isabella
Velicogna of University of
California
at Irvine, a member of the
research team.
If the ice
sheets continue to melt faster
and faster, sea levels
could rise
56 centimetres by 2100, "which is
much bigger than what we
were
thinking just three years ago",
says Velicogna. As such, ice
sheets
would become the dominant
contributor to sea level rise
this
century.
While the
study cannot separate out the
effects of climate change
from
natural variability, the trend is
worrying. "It fits into a
pattern
that we'd expect of ice sheet
response to climate change,"
says
glaciologist Ian Howat of the
Ohio State University in
Columbus.
"Whatever
processes are driving the mass
loss are intensifying. The
picture is
getting worse, not
better."
Journal
reference: Geophysical Research
Letters,
DOI:10.1029/2011GL046583
