Here’s what you’ll learn when you read this story:

• Sea level rise is an immediate threat caused by climate change and driven in large part by melting glaciers and ice sheets.
• A new study found that hidden channels beneath ice sheets could trap warm water and accelerate the ice’s deterioration, leading to instability that causes land ice in Antarctica to flow into the ocean.
• These small-scale warming processes need to be included in future models to form a more accurate picture of how sea-level rise will impact the world in coming decades.

Understanding sea level rise is complicated. A team of scientists working with the UN’s Intergovernmental Panel on Climate Change (IPCC) makes its best estimates using the most up-to-date understanding of glacier and ice shelf dynamics, but as past studies have shown, these features are being pushed to a point never before witnessed. As a result, understanding the behavior of these complicated natural systems is far from simple.

Take, for example, the Fimbulisen Ice Shelf. Located in East Antarctica, this ice shelf is (thankfully) in an especially cold part of the frozen continent, making it less vulnerable than the Thwaites Glacier—also known as the “doomsday glacier”—in warmer West Antarctica. But scientists from the iC3 Polar Research Hub in Tromsø, Norway, have discovered hidden mechanisms beneath the Fimbulisen Ice Shelf that could radically alter our sea level rise timeline. The results of their study were published in the journal Nature Communications.

“We found that the shape of the ice shelf underside is not just a passive feature,” Tore Hatterman, lead author of the study from iC3, said in a press statement. “It can actively trap ocean heat in exactly the places where extra melting matters most.”

Underneath the Fimbulisen Ice Shelf, small channels can create circulation systems that keep warm water trapped against the glacier itself. This can increase the melting rate of the glacier by an order of magnitude, while also leading to other instabilities that leave the ice shelf more vulnerable than scientists originally expected.

Exploring the underside of a glacier is far from easy. In early 2024, an underwater research project by the University of Gothenburg suffered a huge setback when its AUV submersible “Ran” disappeared beneath the icy depths of Thwaites Glacier. In the current study, scientists used a detailed map of the underside of the Fimbulisen Ice Shelf coupled with advanced modeling of the ocean cavity that lies beneath it. They then compared two ice-shelf-underside conditions—smooth or channeled—in both cooler and warmer water conditions, which gave them a good idea of how the channels impact temperature and water mixing.

“We observed beneath the Fimbulisen Ice Shelf that even small amounts of warmer water can substantially increase melting within the channels,” Hatterman said in a press statement. “As a result, the channels can grow and, in the worst case, weaken the stability of the entire ice shelf.”

If these channels do indeed grow in size and weaken the overall structure, they may eventually cause the ice shelf to fail and allow land ice to flow into the ocean. In 2023, National Oceanic and Atmospheric Administration (NOAA) scientist Nicole Schlegel explained why such an outcome could be disastrous.

“Thousands of meters of ice sit on land,” Schlegel said in a NASA press statement. “If the ice shelves are thinned or changed, then that decreases their ability to hold back the ice that’s on the land. More interior ice comes into the ocean, it speeds up, then you have a contribution to sea level rise.”

Future models will have to include what the researchers call “small-scale melting processes” that can end up having very large consequences. If not, humanity could end up forging ahead without knowing just how great the threat truly is.