Looking into the evolution of the East Antarctic ice sheet, researchers have found that it is not as stable as previously thought and could shrink dramatically in future, leading to a significant rise in sea levels that could flood major US cities such as Florida.

The massive East Antarctic ice sheet has long been considered more stable and permanent than the sheets in West Antarctica and Greenland.

However, in a new study published in journal Nature, researchers have posited that certain regions of East Antarctic ice sheet have been losing and expanding for millions of years and are more vulnerable to melting than ever thought.

The researchers got to this conclusion after analysing East Antarctica's Sabrina Coast – a region located near glaciers that flow from Aurora basin and which could be susceptible to climate change due to ocean warming.

They used marine seismic technology to reconstruct the evolution of the ice sheet in this region over past 50 million years and found that during warm climates in the past, when atmospheric temperatures were similar or higher than the present day, the ice sheet was much wetter and more unstable than now.

"We have evidence for a very dynamic ice sheet that grew and shrank significantly between glacial and interglacial periods," said study co-author Sean Gulick. "There were also often long intervals of open water along the Sabrina Coast, with limited glacial influence."

During first 20 million years of the ice sheet's history, ice advanced from the Aurora Basin and retreated back again as many as 11 times. However, about 6 million years ago, the sheet expanded and stabilised, much like how we see it now.

The wild fluctuations have raised fears that the sheet could again go back to the unstable zone with the rise in global air temperatures. If this happens, there would be a dramatic rise in global sea levels, enough to flood major US cities such as Florida.

"There is enough ice in our study region alone to raise global sea level by as much as 15 feet," says another study author Amelia Shevenell. This, as the researcher says, could prove catastrophic for Florida, which sits far away from Antarctica.

"A lot of what we are seeing right now in the coastal regions is that warming ocean waters are melting Antarctica's glaciers and ice shelves, but this process may just be the beginning," Shevenell adds. "Once you have that combination of ocean heat and atmospheric heat—which are related—that's when the ice sheet could really experience dramatic ice mass loss."