Earth’s sea levels should be 30 feet higher than they are – and dramatic melting in Antarctica may soon plug the gap, scientists warn.

They say that global temperatures today are the same as they were 115,000 years ago, a time when modern humans were only just beginning to leave Africa.

Research shows that during this time period, known as the Eemian period, scorching ocean temperatures caused a catastrophic global ice melt.

As a result, sea levels were 20 to 30 feet higher than they are today.

But if modern ocean temperatures are the same as they were during the Eemian, that means our planet is “missing” a devastating sea rise.

If oceans were to rise by just six feet, large swathes of coastal cities would find themselves underwater, turning streets into canals and completely submerging some buildings.

Large parts of New York, San Francisco, and Los Angeles would be submerged.

Scientists think that sea levels made this jump 115,000 years ago because of a sudden ice collapse in Antarctica.

The continent’s vulnerable West Antarctic ice sheet – which is already retreating again today – released a lot of sea level rise in a hurry.

“There’s no way to get tens of feet of sea level rise without getting tens of feet of sea level rise from Antarctica,” said Dr. Rob DeConto, an Antarctic expert at the University of Massachusetts.

His team created state of the art computer models that showed how Antarctic ice responded to warm ocean temperatures during the Eemian period.

They showed that two processes, called marine ice cliff collapse and marine ice sheet instability, rapidly melted the West Antarctic ice sheet.

They exposed thick glaciers that formed part of the ice sheet to the ocean, meaning the ice blocks floated out to sea more quickly. There they quickly melted, adding thousands of tons of water to the world’s oceans.

Scientists warn that if ice shelves in Antarctica undergo similar processes today it could spell disaster for Earth.

Combined with melting in Greenland, we could see sea levels rise much as six feet in this century.

In the next century, ice loss would get even worse.

“What we pointed out was, if the kind of calving that we see in Greenland today were to start turning on in analogous settings in Antarctica, then Antarctica has way thicker ice, it’s a way bigger ice sheet, the consequences would be potentially really monumental for sea level rise,” DeConto said.