Global Warming Five Million Years Ago in Antarctic Drastically Raised Sea Levels

First Posted: Jul 22, 2013 07:21 AM EDT

As temperatures rise, scientists continue to worry about the effects of melting Antarctic ice, which threatens to raise sea levels and swamp coastal communities. This event, though, isn't unprecedented. Researchers have uncovered evidence that reveals global warming five million years ago may have caused parts of Antarctica's ice sheets to melt, causing sea levels to rise by about 20 meters.

Learning about our planet's past weather might help us better understand future conditions. That's why researchers set out to learn about ancient melting of the East Antarctic ice sheet by studying mud samples. After examining the samples, they found that melting took place repeatedly between five and three million years ago, during a geological period called the Pliocene Epoch. This period was known for its global cooling and aridity, which occurred after the warmer Miocene. Yet at the time, sea levels probably rose about 10 meters.

Despite the fact that the Pliocene Epoch was cool in comparison to the Miocene, it was still warmer than temperatures are today. The also period had similar carbon dioxide concentrations to today. In addition, its temperatures were comparable to those predicted for the end of this century. This means that studying this particular period in our Earth's history could reveal insights into our future.

"The Pliocene Epoch had temperatures that were two or three degrees higher than today and similar atmospheric carbon dioxide levels to today," said Tina Van De Flierdt, co-author of the new study, in a news release. "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."

It's not surprising that sea levels rose so high in the past. The East Antarctic ice sheet is the largest ice mass on Earth and is roughly the size of Australia. Although it has fluctuated in size since its formation about 34 million years ago, it probably stabilized around 14 million years ago. Now, though, warmer temperatures may cause melting that could affect countries across the world.

"Scientists previously considered the East Antarctic ice sheet to be more stable than the much smaller ice sheets in West Antarctica and Greenland, even though very few studies of East Antarctic ice sheet have been carried out," said Carys Cook, one of the researchers, in a news release. "Our work now shows that the East Antarctic ice sheet has been much more sensitive to climate change in the past than previously realized. This finding is important for our understanding of what may happen to the Earth if we do not tackle the effects of climate change."

The findings are published in the journal Nature Geoscience.

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