One of Antarctica’s largest ice shelves, Larsen C, has been losing volume for years. Its two neighboring ice shelves have both disintegrated within the last two decades. And now researchers say the vulnerable ice shelf will most likely collapse within a century—maybe sooner, and with little warning. Rising air temperatures and warmer ocean currents are thinning Larsen C from both above and below, according to findings published in The Cryosphere this week.

Over the last half-century, the Antarctic Peninsula has been experiencing the biggest temperature jumps on the planet. Its west coast is one of the fastest warming places on Earth, with average annual temperatures rising 2.5 degrees Celsius in the last five decades.

Ice shelves are floating extensions of the much larger, grounded ice sheet, and they’re made of freshwater that originally fell down as snow. Because they’re already floating, their breaking apart shouldn’t contribute to sea level rise—unless, of course, they were holding ice back from crashing into the water. Unfortunately, that’s exactly the case: “If this vast ice shelf... were to collapse, it would allow the tributary glaciers behind it to flow faster into the sea,” British Antarctic Survey’s Paul Holland says in a news release.

For years, researchers weren’t sure if the thinning came from the surface of Larsen C or from beneath it. When Holland and colleagues combined satellite data with eight radar surveys spanning 1998 through 2012, they discovered that the ice shelf had lost four meters (13 feet) of ice in that time, and the surface was about a meter (3 feet) lower.

“What’s exciting about this study is we now know that two different processes are causing Larsen C to thin and become less stable,” Holland explains. “Air is being lost from the top layer of snow (called the firn), which is becoming more compacted—probably because of increased melting by a warmer atmosphere. We know also that Larsen C is losing ice, probably from warmer ocean currents or changing ice flow.”

Larsen A collapsed in 1995, and Larsen B collapsed in 2002. Larsen C is about 10 times bigger than B, stretching across 50,000 square kilometers (19,300 square miles)—that’s slightly smaller than Scotland or West Virginia. Based on the crack that’s forming, the ice shelf may retreat back further than researchers previously thought. It also appears to be detaching from a small island called Bawden Ice Rise on its northern edge.

“When Larsen A and B were lost, the glaciers behind them accelerated and they are now contributing a significant fraction of the sea-level rise from the whole of Antarctica,” says David Vaughan of the British Antarctic Survey. “Larsen C is bigger and if it were to be lost in the next few decades then it would actually add to the projections of sea-level rise by 2100.” Around the world, that rise will be something in excess of 50 centimeters higher than today’s levels.

Images: Adam Clark (top) & Pete Bucktrout (middle), British Antarctic Survey