Apr 11, 2017

Scientists just uncovered some troubling news about Greenland’s most enormous glacier

Jakobshavn Glacier
Chris Mooney
Washington Post
The calving front of Jakobshavn glacier. Photo: NASA’s Digital Mapping System team
The calving front of Jakobshavn glacier. Photo: NASA’s Digital Mapping System team

Jakobshavn glacier, responsible for feeding flotillas of icebergs into the Ilulissat icefjord — and possibly for unleashing the iceberg that sank the Titanic — is an enormous outlet for the larger Greenland ice sheet, which itself contains enough ice to raise seas by more than 20 feet.

Of that ice, more than 6 percent flows toward the ocean through Jakobshavn, which has raced inland since the 1990s, pouring ever more of its mass into the seas — a change that scientists believe has been caused by warming ocean temperatures. If all of the ice that flows through this region were to melt, it would raise global sea levels by nearly two feet. Just from 2000 to 2011, the ice loss through Jakobshavn alone caused the global sea level to rise by a millimeter.

The U.S. east coast in particular is already a “hot spot” for sea level rise, with rates in many areas exceeding the current global average of a little over 3 millimeters per year.

But until now, researchers have not been sure how far Jakobshavn’s ice extends below sea level — or how much deeper it gets further inland. That’s crucial because Jakobshavn is undergoing a dangerous “marine ice sheet instability,” in which oceanfront glaciers that grow deeper further inland are prone to unstoppable retreat down what scientists call a “retrograde” slope.

That’s where the new science comes in: Researchers who flew over Jakobshavn in a helicopter toting a gravimeter, used to detect the gravitational pull of the ice and deduce its mass, say they’ve found the glacier extends even deeper below sea level than previously realized, a configuration that sets the stage for further retreat.

“The way the bed looks, sort of makes it more prone to continuous retreat for decades to come,” said one of the study’s authors, Eric Rignot, a researcher with NASA’s Jet Propulsion Laboratory and the University of California-Irvine.