Researchers have found that the East Antarctic ice sheet melted in at least one region about three million years ago, when climate conditions were similar to where global warming seems to be taking us.
A NASA flying laboratory passes Antarctica?s tallest peak during a flight over the continent to measure changes in the ice sheet and sea ice in 2012. A recent study found that the East Antarctica ice sheet melted some five million years ago - and could do so again.
Michael Studinger/NASA/Reuters
EnlargeA coastal region of the largest ice sheet in the world melted millions of years ago ? and could again.
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During the Pliocene epoch some five million to two million years ago,?the East Antarctic ice sheet retreated more than a hundred miles, researchers have found. That finding contradicts models showing that the enormous ice sheet has been stable over the last several million years and suggests that future melting from the sheet could contribute to sea level rise if global warming is not abated.
?If carbon dioxide levels and global temperatures continue to rise, the East Antarctic ice sheet may become increasingly vulnerable to large changes, like those that took place during the Pliocene,? said Carys Cook, a research postgraduate from the Grantham Institute for Climate Change at Imperial College London and a co-author on the study, published in Nature Geoscience.
The East Antarctic ice sheet, home to the South Pole, is the largest ice mass on Earth and one of two large sheets blanketing Antarctica. Scientists have generally agreed that the ice sheet?s counterpart, the West Antarctic ice sheet, along with the Greenland ice sheet are rapidly shedding thier mass and contributing to a rise in the average global sea level, which over the past 20 has been rising at a rate of about 0.13 inches a year.?
But the East Antarctic ice sheet has been more inscrutable. Studies have disagreed over whether the sheet is currently gaining or losing mass, a disagreement mostly caused by disparities in where the data is collected from the sheet, some parts of which are more vulnerable to melting than others, said Dr. Cook.
And the ice sheet?s past is even more enigmatic than its present. Most models, drawing on global sea level data, have shown that the sheet has been stable over the past 14 million years and is unlikely to exhibit melting in the future.?
But now a series of studies, which this latest project bookends, have indicated just the opposite. Using evidence drilled directly from the remote Antarctic ice, scientists have shown that the sheet was in fact dynamic about three million years ago.
"Up to now, most studies looking at the past stability of the East Antarctic ice sheet have been based on indirect records that are from locations really far away from Antarctica, and therefore may not provide as full a picture of what was happening there as records retrieved from right next to the continent,? said Cook.
Researchers studied the geochemical signature of marine sediments drilled from depths about 1.8 miles below sea level off Antarctica?s coast. The sediments were chemically traced back to the Wilkes Subglacial Basin, a low-lying edge of the sheet lapped by increasingly warm seawater.
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