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Global Warming in the Past Caused Massive Melting in Antarctica, Rise in Sea levels by 20 Meters

Jul 22, 2013 08:06 AM EDT

A latest study has shown that even relatively stable ice sheets in Antarctica dramatically shrunk and increased sea levels by up to 20 meters or about 60 feet due to global warming that occurred millions of years ago.

The study was conducted by scientists at the Imperial College London and colleagues who found that during Pliocene Epoch, the ice-sheet in Antarctica melted repeatedly that led to the rise in sea level by about 10 meters. Other researchers had previously found that the ice-sheets of West Antarctic and Greenland partially melted during this period that led to the rise of sea-level by another 10 meters, bringing the total sea-level rise to 20 meters.

The Pliocene epoch (5.3 to 2.6 million years ago) was relatively cool compared to the previous warmer Miocene. This epoch saw the spread of grasslands that led to the evolution of many grazers we see today. There was also some landmark tectonic activity during the period as the tectonic plates of North and South America joined during this era.

The East Antarctic ice sheet, which was studied in the present research, has been considered to be stable since the past 14 million years. The ice sheet is about the size of Australia and had formed about 34 million years ago.  According to researchers, understanding glacial melting during the Pliocene epoch helps with the understanding of the current melting trends as Pliocene epoch also had high levels of greenhouses gases.

Note that the temperatures during the Pliocene epoch were cooler than the epochs that preceded it but, warmer than current global temperatures

"The Pliocene Epoch had temperatures that were two or three degrees higher than today and similar atmospheric carbon dioxide levels to today. Our study underlines that these conditions have led to a large loss of ice and significant rises in global sea level in the past. Scientists predict that global temperatures of a similar level may be reached by the end of this century, so it is very important for us to understand what the possible consequences might be," Dr Tina Van De Flierdt, co-author from the Department of Earth Science and Engineering at Imperial College London, said in a news release.

In the present study, researchers analyzed mud samples to learn about the melting of the ice-sheet in East Antarctica during the Pliocene epoch. They found that the ice-sheets melted during this stable and somewhat cooler period. The samples for the study were obtained at depths of nearly two miles, off the coast of Antarctica.

Chemical Analysis of the mud samples gave researchers a fingerprint which they used to track the origins of the mud in the continent. Their research showed that the mud deposited on the sea bed could have only come from the mud that's under the ice-sheet. The only way for the mud to find its way to the sea would be when the ice melted and eroded the rocks below it.  Also, since much of the ice during that period rested in basins below sea-levels, it was always in contact with sea water. Thus, global temperatures that warmed the water affected the ice-sheets.

"Our work now shows that the East Antarctic ice sheet has been much more sensitive to climate change in the past than previously realised. This finding is important for our understanding of what may happen to the Earth if we do not tackle the effects of climate change," said Carys Cook, research postgraduate from the Grantham Institute for Climate Change at Imperial and co-author of the study.

The study is published in the journal Nature Geoscience.

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