When somebody says something is happening at a “glacial pace”, they usually mean “as slow as a glacier.” In other words, really, really slow. But, the ice under eight of Antarctica’s largest glaciers is melting really, really fast—five times faster than it should. That piece of alarming news comes from a study published April 2 in the scientific journal Nature GeoScience (https://www.nature.com/articles/s41561-018-0082-z).
You’ve probably seen videos of enormous chunks of ice breaking off glaciers and slamming into the sea. That is still happening, but scientists have discovered that much of the real action in the Antarctic is out of sight, hundreds of feet inland, and under water so deep that even remote submersibles can’t get there.
Here’s the bottom line, according to the study: climate change is warming the Southern Ocean’s waters, causing the floating Antarctic Ice Shelf to melt from its undersea base upward. The scientists believe that the entire ice sheet—the largest in the world—might crack and collapse completely within 100 years. This would cause sea levels around the globe to rise about 10 feet, flooding low-lying islands and coastal areas.
Climate scientist Hannes Konrad, of the University of Leeds in England, is the study’s lead author. “Our study provides clear evidence that retreat is happening across the ice sheet due to ocean melting at its base,” he wrote. “This retreat has had a huge impact on inland glaciers, because releasing them from the sea bed removes friction, causing them to speed up and contribute to global sea level rise.”
Konrad and his colleagues at the university’s Center for Polar Observation and Modelling used satellite imagery and buoyancy equations to figure this out. They’ve calculated that the submerged ice is retreating across approximately 10,000 miles of Antarctica’s coastline; that’s about ⅓ of the continent’s perimeter.
The scientists zeroed in on a geographic feature called “grounding lines”; these are vertical lines projected up from submerged points where glacier ice connects with solid ocean bedrock. On one side of a grounding line, the ice sheet sits right on the ocean floor; on the other, the ice sticks out like a shelf, and can float more than half a mile above the sea floor. As a melting glacier’s grounding line retreats inland, the faster-moving inland ice collides with the attached ice shelf and eventually breaks off into the sea.
Grounding line retreat is normal, but its present pace is highly abnormal, especially in western Antarctica, according to the study. Typically, these glaciers recede about 82 feet a year, but the scientists discovered that some of them are now zipping along at 600 feet per year. The result, so far, is this: between 2010 and 2016, 565 square miles of submerged Antarctic ice melted—an area that’s about the size of the City of London, England. To be clear, the accelerated melting seems to be confined to the western side of the continent, for reasons unknown.