Climate

Antarctic glacier saw the fastest retreat in modern history; it could spell trouble for sea levels, report finds    

Hektoria Glacier terminus in February 2024 during field work. The glacier continues to calve giant icebergs into the sea.

 

An Antarctic glacier shrunk by nearly 50% in just two months, the fastest retreat recorded in modern history, according to a new study — and the way it retreated could have big implications for global sea level rise.

The Hektoria Glacier, roughly the size of Philadelphia, is on the Antarctic Peninsula, a spindly chain of mountains sticking off the continent like a thumb pointing toward South America. It is one of the fastest warming regions on Earth.

Grounded glaciers like Hektoria, which rest on the seabed and don't float, generally retreat no more than a few hundred meters a year. But between November and December 2022, Hektoria retreated by 5 miles, according to the study published Monday in the journal Nature Geoscience. "This is astonishing; the rate of retreat is just crazy," said Ted Scambos, a study author and senior research scientist for the Earth Science and Observation Center at the University of Colorado Boulder.

Understanding more about why this happened is vital; if larger glaciers retreat at similar rates, it could have “catastrophic implications for sea level rise,” the authors wrote in a statement accompanying the report. Antarctica holds enough ice to raise global sea level by around 190 feet.

Hektoria's near demise was discovered by chance. Researchers had been surveying the bay where it's located for a separate study. They were keeping a close eye on the area's “fast ice” — sea ice fastened to land that doesn't move with the wind or tides — believing it was about to break off and float out to sea.

As Naomi Ochwat, a study co-author and postdoctoral associate at the University of Colorado Boulder, pored over the data, she noticed Hektoria had lost an enormous amount of ice over a very short period. “I realized that, OK, something special is going on here,” Ochwat told CNN. She and her co-authors started to dig into what was happening, looking at satellite images and data from flyovers. They identified several steps that led to Hektoria's rapid retreat. In 2011, the bay filled with fast ice, stabilizing the glaciers around it, allowing them to advance into the bay and form thick, floating ice tongues. In 2022, this fast ice broke out of the bay, destabilizing the glaciers, causing them to lose their ice tongues and retreat.

The reason Hektoria fell apart much faster than its neighboring glaciers is due to what lies beneath it, the scientists found.

Hektoria rests on an ice plain, where sliding ice glides over flat sediment on the seabed. Ice plains can prompt fast retreat because as the glacier thins, the ice starts to rise up and water pushes underneath into its crevasses, exerting pressure and causing large slabs to break off — in a process called calving As one iceberg calves, it exposes the glacier behind it to the same pressures and calving happens again. Scambos likens the process to “dominoes toppling backwards, their feet slipping out from under them, one after the other.”

This kind of ice plain melting has happened before. Models show that between about 15,000 and 19,000 years ago, during a period of warming that ended the last Ice Age, glaciers with ice plains retreated hundreds of meters a day. But “we hadn't seen it play out live before, certainly not at this rate,” Ochwat said.

Hektoria's retreat was heavily influenced by climate change, she added. The loss of sea ice in the ocean next to Hektoria, believed to have been driven by ocean warmth, allowed wave swells to reach the fast ice and break it up, leaving the glacier exposed to ocean forces.

As climate change accelerates, “we are likely to see more reductions of sea ice in this region,” said Bethan Davies, a glacial geologist at Newcastle University who was not involved in the study. This could result in other glaciers losing the sea ice that currently buttresses them, she told CNN. Hektoria is a relatively small glacier by Antarctic standards, and its partial demise won't cost the planet much in terms of sea level rise, Scambos said. However, “it’s a smaller cousin to some truly gigantic — I mean size of the island of Britain — glaciers in Antarctica that could conceivably go through the same process, as this whole evolution of the ice sheets on Earth evolves with global warming,” he added.

The next stage is to better establish which areas in Antarctica are vulnerable to the same process. If a huge glacier were to disintegrate quickly, “it means that we might have a step change in sea level rise,” Ochwat said.

Rob Larter, a marine geophysicist at the British Antarctic Survey, who was not involved in the research, said the new findings “raise the bar on our understanding of how fast Antarctic glaciers may retreat.”

These glaciers, especially the cavities beneath their ice shelves and tongues, are some of the most inaccessible environments on Earth, CNN has told, but knowing more about them is crucial to better project how they'll respond to climate change. The research raises fears that ice loss from Antarctica, which contributes to sea-level rise, “could occur more rapidly than projected,” he said.

It's yet another sign humanity still has a lot to learn about this vast, isolated continent. “We're in a position where we're still uncovering processes that we didn't know about,” Ochwat said.