The demise of Greenland’s ice sheet seems to be accelerating with the oldest and thickest ice melting twice as fast as young ice, according to a new study in the American Geophysical Union’s (AGU’s) journal Geophysical Research Letters.

For years, researchers thought that the Greenland’s ice sheet, the world’s second-largest reservoir of fresh water, would be the so-called “last ice area” or the final place to lose the presence of year-round ice. Ice in the ocean north of Greenland is older and thicker than anywhere else in the Arctic, but it actually appears to be the most vulnerable, according to the new study. In fact, it’s “declining twice as fast as ice in the rest of the Arctic.”

While most of the ice covering the Arctic is about one to four years old while the ice in the “last ice area” is more than five years old and can measure more than 13 feet thick, according to the National Snow and Ice Data Center. The ice is now becoming thinner in two subregions of that area, which combined have lost five feet of ice since the late 1970s, according to the new study.

“We can’t treat the Last Ice Area as a monolithic area of ice which is going to last a long time,” Kent Moore, an atmospheric physicist at the University of Toronto in Canada and the lead author of the new study, said in a statement. “There’s actually lots of regional variability.”

The group determined that the reason the ice is melting far faster than previously reported is that it is more mobile than they thought. The team modelled sea ice cover, thickness and motion in “last ice area” during a 40-year time period, based on satellite observations and atmospheric data. They found that the older, thicker ice moves with the ocean currents and atmospheric winds traveling to other areas of the sea.

“Historically, we thought of this place as an area that just receives ice,” David Barber, an Arctic climatologist from the University of Manitoba in Canada says in a statement. “But these results are teaching us that this is a dynamic area.”

The report comes in the wake of an earlier study published in the Proceedings of the National Academy of Sciences, which revealed that Greenland’s massive ice sheets are melting twice as fast as they were just a decade ago. As the Greenland ice sheet melts, it has caused the sea level to rise a quarter inch in just the past eight years. Since Greenland has enough ice to raise global sea levels by 25 feet, the new melt rate estimation outlines an alarming prospect and one that is not expected to slow down.

“If you look at climate model projections, we can expect to see larger areas of the ice sheet experiencing melt for longer durations of the year and greater mass loss going forward,” University of Georgia ice scientist Tom Mote told Seth Borenstein at the Associated Press in August. “There’s every reason to believe that years that look like this will become more common.”

While Greenland’s ice has been shrinking during the warm summer months for decades, the PNAS report reveals that Greenland’s ice hasn’t developed any new mass since 1998, suggesting that even the cold season has become too warm for new ice to form.

“The glaciers are still being pushed out of balance,” Eric Rignot, a senior scientist at NASA and an author of the paper, told Robinson Meyer at The Atlantic in April. “Even though the ice sheet has [sometimes] been extremely cold and had low surface melt in the last year, the glaciers are still speeding up, and the ice sheet is still losing mass.”

The Atlantic’s Meyer notes that Greenland has already lost 4,976 gigatons of water since 1972, enough water to fill 16 trillion bathtubs. Researchers predict the Arctic could be ice-free in the summers as early as 2030.