Danish territory of Greenland is a vast arctic landmass off the northeastern
coast of Canada. The sparsely-populated
island is largely covered by a massive ice sheet. But warming artic temperatures linked to global carbon emissions
are causing that ice to melt. According
to a recent climate survey, Greenland's
ice-free area increased by 16 percent
between 1979 and 2002. A new study shows how a closer look at
Greenland's past could help us predict its future.
Lunt is a paleoclimate scientist. That means he studies the earth's history to
understand how the planet's climate works.
A recent study led him to ask not why is the Greenland ice sheet
melting, but rather: how did all that ice get there in the first place?
its early days, 56 to 40 million years ago, Lunt says Greenland was a much
different place from what it is today. He looked at similar latitudes from the
present day and from modeling studies to conclude, "It is quite likely
there were bare soil and unvegetated areas, but also a high probability that
there were areas that were covered in grass and even forests."
says Greenland's ancient history was rubbed clean by glaciers – broad,
slow-moving rivers of freshwater ice.
Picking up rocks and other debris as they inched forward, Greenland's
glaciers eventually reached the coasts, where they dropped huge icebergs, and
their accumulated debris, into the sea.
can actually go to some of these places in the North Atlantic around the
margins of Greenland and drill down and actually extract the sediment that's on
the ocean floor," Lunt says.
Around three million years ago the scientists find a sharp increase in
the amount of small rocks and debris deposited by icebergs.
theories for ice analyzed
and colleagues at the University of Bristol in England used climate and ice
sheet computer models to analyze four popular theories to explain the ice sheet
formation. The hypotheses range from changes in ocean circulation, or the
increasing height of the North American Rocky Mountains, to changes in the
earth's orbit or the natural changes in atmospheric greenhouse gas
says carbon dioxide showed a more important effect than the others. "In some of the simulations that we
looked at, it was actually the only one of those four theories that was able to
cause a large increase in ice."
says the levels of CO2 in the atmosphere today are rapidly approaching 400
parts per million or the level of atmospheric CO2 when Greenland was ice-free. "But what you cannot say," he
says, "is that as we approach 400 that the Greenland ice sheet will
suddenly disappear because the ice sheets don't work in a linear fashion. It may be because the ice sheet is there
now, at the moment it is more robust that we can go up that high and still
maintain the ice sheet."
new study is published in the British journal Nature. The work was carried out with funding from
the British Antarctic Survey and Research Council.