According to a recent scientific study, the collapse of the West Antarctic Ice Sheet (WAIS) would only raise sea levels by half of the originally estimated amount. Rather than forcing waters worldwide up by five to six meters (15 to 20 feet), a catastrophic meltdown will only generate a 3.3-meter (11-foot) lift, a British research team say. Their study was published in the Friday edition of the prestigious journal Science, and argues that the potential impact on US cities remains catastrophic.

“The long-term impact of West Antarctica is not as serious as previously believed. But 17 million people in Bangladesh alone would be displaced by a sea level rise of 1.5 meters. The consequences for the planet and stability of society as a whole for even a 1-2 meters rise is very, very serious,” Jonathan Bamber, who is a professor at Bristol University, in the UK, and also the leader of the new Science study, tells Reuters.

At this point, experts add, the WAIS is the most vulnerable stretch of ice in the world, far more so than that of Greenland or the ices of East Antarctica.

“Levels on the US seaboards would rise 25 percent more than the global average and threaten cities like New York, Washington DC, and San Francisco,” experts from the US-based University of Colorado in Boulder (UCB) explain in a statement. Bamber is currently a visiting fellow at the UCB.

For the new study, the scientists have collaborated with colleagues from the University of Durham, in the UK, and the Delft University of Technology, in the Netherlands. The results unequivocally show that the rise in sea levels will be more significant near US borders than the global average.

Because of its vast size, Antarctica exerts what experts call a gravitational tug on the waters of the Southern Ocean, making them a bit higher than the global mean. But, if the massive ice spreads of the WAIS were to collapse, that excess water would have nothing to hold it in place, and would most likely move in a wave towards the Northern hemisphere. There, models predict it would remain elevated, whereas the Southern Ocean would experience a drop in its average levels.

Bamber has also drawn attention to the fact that the sea levels could further increase, by the end of this century, if other ice sheets go as well. His research has been solely focused on the WAIS, but important spreads of ice in the eastern part of Antarctica and in Greenland are also at risk of collapsing. If that happens, the level of worldwide water will increase even further, affecting additional tens of millions across the world.