Earth Is 'Missing' at Least 20 Ft of Sea Level Rise. Antarctica Could Be The Time Bomb

Some 115,000 years ago, Homo sapiens were still living in bands of hunter gatherers, largely confined to Africa. We still shared the globe with the Neanderthals, although it's not clear we had met them yet.

And though these various hominids didn't know it, the Earth was coming to the end of a major warm period. It was one that's quite close to our current climate, but with one major discrepancy - seas at the time were 20 to 30 feet (6 to 9 metres) higher.

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During this ancient period, sometimes called the Eemian, the oceans were about as warm asthey are today.

And last month, intriguing new research emerged suggesting that Northern Hemisphere glaciers have already retreated just as far as they did in the Eemian, driven by dramatic warming in Arctic regions.

The finding arose when a team of researchers working on Baffin Island, in northeastern Canada, sampled the remains of ancient plants that had emerged from beneath fast-retreating mountain glaciers.

And they found that the plants were very old indeed, and had probably last grown in these spots some 115,000 years ago.

That's the last time the areas were actually not covered by ice, the scientists believe.

"It's very hard to come up with any other explanation, except that at least in that one area where we're working ... the last century is as warm as any century in the last 115,000 years," said Gifford Miller, a geologist at the University of Colorado in Boulder who led the research on Baffin Island.

But if Miller is right, there's a big problem. We have geological records of sea levels from the Eemian. And the oceans, scientists believe, were 20 to 30 feet (6 to 9 metres) higher.

Some extra water likely came from Greenland, whose ice currently contains over 20 feet (6 metres) of potential sea level rise. But it couldn't have been just Greenland, because that entire ice sheet did not melt at the time.

That's why researchers also suspect a collapse of the most vulnerable part of Antarctica, the West Antarctic ice sheet. This region could easily supply another 10 feet (3 metres) of sea level rise, or more.

"There's no way to get tens of meters of sea level rise without getting tens of meters of sea level rise from Antarctica," said Rob DeConto, an Antarctic expert at the University of Massachusetts.