The formation of a giant iceberg could spell the beginning of the end for Larsen C.

By Bob Berwyn

Ice meets the sea along the coast of the Antarctic Peninsula. (Photo: Bob Berwyn)

Larsen C, the last big ice shelf along the shore of the Antarctic Peninsula, is getting ready to shed an iceberg bigger than Rhode Island. It’s just the latest sign that the continent’s frozen fringes are crumbling. The 5,000-square kilometer (1,930 mile) slab of ice is separating along a crack that’s growing several miles.

“It’s primed to go within the next few weeks, because of the speed at which the crack is accelerating,” says Hamish Pritchard, an ice dynamics and paleoclimate expert with the British Antarctic Survey. The ice scientists stationed at nearby Rothera Research Station are making day trips to the crack and using radar data to measure the calving event in real time.

“The calving of this large iceberg could be the first step of the collapse of Larsen C ice shelf, which would result in the disintegration of a huge area of ice into a number of icebergs and smaller fragments,” the BAS said Friday in a news release.

Ice shelves are essentially floating extensions of land-based glaciers. When the giant floating slabs of ice break apart and retreat from the shore, the glaciers speed up, melt in the ocean, and raise global sea level. That’s bad news for tens of millions of people who live along low-lying coastlines in warmer parts of the world—places like Amsterdam, New York, Miami, Bangladesh, and Dhaka.

In the 1990s and early 2000s, the Antarctic Peninsula warmed much faster than the global average, says Ted Scambos, lead scientist for the Boulder-based National Snow and Ice Data Center.

“The Peninsula has an interesting history. In 1995, the Larsen A ice shelf disintegrated during a warm summer. It was covered with melt water that seeps down and fractures the ice. In 2002, a larger area, Larsen B, broke apart. That was fairly spectacular and kicked off a lot more interest,” says Scambos, who is heading to Antarctica this month.

“Big icebergs breaking off is one of the first indications of instability in shelves.���

“What we found out around the time of the Larsen B disintegration is that the glaciers accelerated tremendously,” Scambos says. “That unloads ice that’s on the continent. And that does contribute to sea level rise, so all eyes have turned to the remaining ice in this area.”

Once the iceberg has calved the big question is whether the entire ice sheet may collapse. This is something that BAS teams have been monitoring and why glaciologists were deployed to work on Larsen C in the past few weeks. BAS scientists have been working in the area for 40 years, mapping the Larsen C ice shelf via dogsled in the early years. Those measurements, Pritchard says, show that climate change has definitely thinned the ice shelf in the past few decades.

Larsen C is much larger than the others in the region, with many small- and medium-size glaciers flowing into it. The potential for the break-up to affect sea level rise is part of the reason scientists are watching it closely. The observations also provide clues for how other, even bigger ice shelves may respond as the climate continues to warm.

“Big icebergs breaking off is one of the first indications of instability in shelves. There have other Larsen C calving events, but none this big. It’s an area that had previously not retreated,” Scambos says. Along with the BAS radar data, more aerial surveys could help foretell the fate of the ice shelf.

Along the Antarctic Peninsula, which juts up toward South America, the ice shelves are mostly melting because of surface warming. In other parts of Antarctica, warm ocean currents are melting the ice shelves from below, starting a process that could melt enough ice to raise global sea level by several feet by 2100.

And everything the scientists have observed so far points to a change that is driven by a warming planet, Scambos says.

“That implies that what we’re seeing is going to continue. I don’t see how it won’t, because everything we’re doing is turning up the volume on this, and that means we’re on track to see some significant level of sea level rise from West Antarctica,” he adds. “The question is, do we want to do something about the greenhouse gas force that is causing this? We have to plan on a century of more changes from a warming planet — what pace of change are we willing to accept? People say, well, it’s inevitable, but there are different levels of inevitable — one is losing most of Florida in a couple of centuries.”