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Aerial surveys show
two glaciers flowing into Johan Petersen fjord in south-eastern
Greenland. The melting of the ice sheet would cause oceans to rise by
six metres around the world if it was lost entirely. Photograph:
Jeremy Harbeck/Icebridge/NASA
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Greenland's
huge annual ice loss is even worse than thought
Ice
cap is disappearing far more rapidly than previously estimated, and
is part of a long-term trend, new research shows
Damian Carrington
@dpcarrington
Thursday 22
September 2016 00.48 BST
The huge annual
losses of ice from the Greenland cap are even worse than thought,
according to new research which also shows that the melt is not a
short-term blip but a long-term trend.
The melting
Greenland ice sheet is already a major contributor to rising sea
level and if it was eventually lost entirely, the oceans would rise
by six metres around the world, flooding many of the world’s
largest cities.
The new study
reveals a more accurate estimate of the ice loss by taking better
account of the gradual rise of the entire Greenland landmass. When
the ice cap was at its peak 20,000 years ago, its great weight
depressed the hot, viscous rocks in the underlying mantle. As ice has
been shed since, the island has slowly rebounded upwards.
Previous satellite
estimates of modern ice losses tried to take this into account, but
precise new GPS data showed much of Greenland is rising far more
rapidly than thought, up to 12mm a year. This means 19 cubic
kilometres more ice is falling into the sea each year, an increase of
about 8% on earlier figures.
The faster rebound
is thought to be the result of hotter, more elastic mantle rocks
under eastern Greenland, a remnant from 40m years ago when the island
passed over the hot spot that now powers Iceland’s volcanoes.
The new work was
also able to reconstruct the ice loss from Greenland over millennia
and found that the same parts of Greenland - the north-west and
south-east - were where most ice is being lost both in the past and
today.
This means the rapid
ice loss recorded by satellite measurements over the last 20 years is
not likely to be a blip, but part of a long-term trend being
exacerbated by climate change. Global warming is driving major
melting on the surface of Greenland’s glaciers and is speeding up
their travel into the sea.
“The fact that we
are seeing such a similarity of past and present behaviour suggests
we could lose ice in these regions for decades into the future,”
said Prof Jonathan Bamber, at the University of Bristol, UK, and one
of the international team of scientists who carried out the new
study, published in Science Advances.
Bamber said the
presence of a long-term trend does not mean global warming is not a
crucial factor: “One thing we can be certain of is that a warmer
atmosphere and a warmer ocean is only going to accelerate this
trend.”
“The headlines of
climate change and melting polar ice are not going to change,” said
Dr Christopher Harig, at the University of Arizona, who was not
involved in the study. “The new research happening now really
speaks to the question: ‘How fast or how much ice can or will melt
by the end of the century?’ As we understand more the complexity of
the ice sheets, these estimates have tended to go up. In my mind, the
time for urgency about climate change [action] really arrived years
ago, and it’s past time our policy reflected that urgency.”
Dr Pippa Whitehouse,
at the University of Durham and also not involved in the new
research, said: “This study highlights the powerful insight that
GPS measurements can give into past and present ice loss. Using such
measurements, this study demonstrates that some of the highest rates
of ice loss across Greenland - both in the past and at present - are
found in areas where the ice sheet flows directly into the ocean,
making it dangerously susceptible to future warming in both the
atmosphere and the ocean.”
Melt water on the
surface of Greenland ice sheet 10 June, 2014 and 15 June, 2016. Every
spring or early summer, the surface of the sheet transforms from a
vast white landscape of snow and ice to one dotted with blue
meltwater streams, rivers, and lakes. In 2016, the transition started
early and fast. Credits: OLI/Landsat 8 and ALI/Earth Observing-1/Nasa
The team behind the
new research said better estimates of continental rebound rates could
be even more significant in estimates of ice loss from the world’s
biggest ice cap, in Antarctica, but that sparse data from the remote
continent made analysis difficult.
In April, very high
temperatures led to a record-breaking early onset of glacier melting
in Greenland, while another satellite study in August reaffirmed the
rapid loss of ice.
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