The original version of this story appeared in Quanta Magazine.
In 2014, NASA made a significant announcement about the West Antarctic Ice Sheet, suggesting it had begun an irreversible retreat. Glaciers on the sheet’s perimeter, which are over 2 kilometers thick, were losing ice faster than snowfall could replenish them. This development raises the critical question of not if the ice sheet will vanish, but rather when. Its disappearance could cause a sea level rise exceeding a meter, affecting areas currently home to 230 million people. Should the entire ice sheet collapse, global coastlines would be dramatically altered, with sea levels potentially rising by an additional 5 meters.
Initially, scientists projected that the glaciers would retreat over several centuries. However, a pivotal study published in Nature in 2016 suggested that collapsing ice cliffs might accelerate this process significantly. This led the Intergovernmental Panel on Climate Change (IPCC) to consider a daunting worst-case scenario: by the year 2100, melting Antarctic and Greenland ice, along with mountain glaciers and seawater expansion, could elevate global sea levels by over 2 meters. If greenhouse gas emissions continue unchecked, projections indicate a potential rise of 15 meters by 2300.
The prospect of a rapid retreat remains contentious among scientists, creating uncertainty about the timeline for the glaciers’ disappearance. If the retreat spans centuries, adaptation may be feasible. Conversely, a swift destabilization could challenge our current ability to respond, especially in major cities like New York, New Orleans, Miami, and Houston, which may not be prepared for such changes.
“We’ve definitely not ruled this out,” remarked Karen Alley, a glaciologist from the University of Manitoba. Her research supports the possibility of the runaway process, yet she cautions, “I’m not ready to say it’s going to happen soon. I’m also not going to say it can’t happen, either.”
Coastal living has thrived during an unusual period of low sea levels, but the oceans are set to rise again. Understanding how ice sheets retreat will be crucial for predicting the future of ports, homes, and the billions living along coastlines.
Grounded by the Sea
Back in 1978, John Mercer, a glaciologist at Ohio State University known for his unconventional fieldwork methods, was one of the first to foresee the threat of global warming to the West Antarctic Ice Sheet. His theory focused on the sheet’s precarious relationship with the sea.
West Antarctica, larger than both Alaska and Texas combined, is separated from East Antarctica by the Transantarctic Mountains, whose peaks are buried under ice. Unlike East Antarctica and Greenland, where ice rests on land above water, West Antarctica’s ice sheet is settled in a depression below sea level, making it especially prone to collapse as seawater laps at its edges.
The massive ice sheet spreads outward under its own weight through glaciers, which don’t stop at the coast but extend over the sea as floating ice shelves. These colossal, floating plates are hundreds of meters thick and act like rafts, supported by underwater formations. They help hold the glaciers back from an inevitable gravitational pull toward the sea.
Original Story at www.wired.com