Though this team focused on the Thwaites Glacier-which is about the size of Florida or Britain-the report follows several others that have raised alarm about how rapidly ice is disappearing in Antarctica, including one study from May which found that the continent's ice sheets are thinning five times faster than they were in the 1990s. The team behind the study, with members from the Georgia Institute of Technology, NASA Jet Propulsion Laboratory, and the University of Washington, says that this hidden instability will likely accelerate water flow into the ocean and raise sea levels much faster than previously estimated.
Modelling simulations suggested extensive ice loss would start in 600 years but the researchers said it could occur sooner depending on the pace of global heating and nature of the instability.
And even if global warming was to later stop, the instability would still push ice out to sea at an "enormously accelerated rate" over the coming centuries.
"It should keep going by itself, and that is the worry", he mentioned.
But he added: "Climate variations will still be important after that tipping point because they will determine how fast the ice will move".
Most of that water is frozen in masses of ice and snow that can be up to 10,000 feet (3 kilometres) thick.
What sounds even more awful is that even if climate change declined and global warming stopped at some point, the glacier would remain unstable and would push ice into the sea at an accelerated rate in the coming centuries.
Together with Greenland's ice sheet, Antarctica's ice sheet contains more than 99 percent of the world's fresh water. And it holds 50 times more ice than all of the mountain glaciers in the world.
But Thwaites prevents its neighbour glaciers from flowing into the ocean, too.
"After reaching the tipping point, Thwaite's Glacier might lose all of its ice in 150 years", Hélène Seroussi, an author of the research and a NASA scientist, mentioned in a press release.
"That would make for a sea level rise of about half a meter (1.64 feet)". This increased uncertainty about future sea level rise but made the worst-case scenarios more likely. This is perhaps the most worrying process from a sea-level perspective: these bits of ice eventually melt in the wider ocean, but the process also speeds up the rate at which glaciers slide into the waters (as they're no longer buoyed up by the ocean), leading to more and more melting.
Maps showing sea level rise risk in Sydney's Eastern Suburbs. That melting gives rise to cavities: An early Manhattan-sized gap was discovered under the Thwaites Glacier in February.
"As more heat and water get under the glacier, it melts faster".
The huge Thwaites glacier covers 293,000sq kms - about half the area of the United Kingdom.
But it's Thwaites' protective effect on neighbouring glaciers that NASA is most anxious about.
That ice loss is part of a broader trend: The entire Antarctic ice sheet is melting almost six times as fast as it did 40 years ago. Within the 1980s, Antarctica lost 40 billion tons of ice yearly.
This would put large swathes of coastal cities underwater, turning streets into canals and completely submerging some towns and cities.