Now, authors of a brand new research report that over the past six years, the speed at which five Antarctic glaciers slough off the ice has doubled.
The situation is so bad that it could happen even under present-day ice-melting rates.
If and when the glacier becomes unstable, the after-effects would be considered "catastrophic".
She explained as the underlying bedrock becomes deeper, undercutting seawater exerts more lift on the glacier - accelerating its flow into the sea. "It will keep going by itself, and that's the worry", said Robel. An "instability" in an ice sheet essentially makes it a frozen, ticking time bomb.
"After reaching the tipping point, Thwaites Glacier could lose all of its ice in a period of 150 years", Hélène Seroussi, an author of the study and a NASA scientist, said in a press release.
The researchers found a precise estimate of how much ice the glacier would shed in the next 50 to 800 years was not possible due to unpredictable climate fluctuations and data limitations.
It found that we're on track to trigger an irreversible instability in the glacier's ice flows.
Study leader Dr Alex Robel, Assistant Professor in Georgia Institute of Technology's School of Earth and Atmospheric Sciences, said: "If you trigger this instability, you don't need to continue to force the ice sheet by cranking up temperatures".
"Once [the] ice is past the grounding line and only over water, it's contributing to sea level because buoyancy is holding it up more than it was before", Robel said. In comparison, sea level rose by 20 centimeter, or almost 8 inches, from the pre-global warming levels and is now blamed for increased flooding in coastal areas.
As the ice melts and crumbles into the oceans, the amount of present water pushes up on coastal areas, threatening floods around the globe.
In other words, even if climate change was magically reversed, it wouldn't necessarily stop the risky and rapid rise in sea levels that could be triggered by unstable ice sheets.
Together with Greenland's ice sheet, Antarctica's ice sheet contains more than 99 percent of the world's fresh water. Why is Antarctic ice the big driver of sea level rise? That melting gives rise to cavities: An early Manhattan-sized gap was discovered under the Thwaites Glacier in February.
Warmer temperatures also heat up the ocean water, which starts eating away at the bottom of the glacier (which raises sea levels). "There is nearly eight times as much ice in the Antarctic ice sheet as there is in the Greenland ice sheet and 50 times as much as in all the mountain glaciers in the world", Robel said.
Glacier collapse has a lot to do with the geometry of the bedrock underpinning the ice.