The major rift in the Larsen C ice shelf pictured in November 2016.
 

John Sonntag/NASA

Delaware-sized iceberg splits from Antarctica

Climate change has a new poster child: a massive iceberg the size of Delawareone of the largest ever recordedthat early this week calved off Larsen C, the largest remaining ice shelf off the Antarctic Peninsula, scientists announced today. Although researchers cannot explicitly connect the calving event to warming air or water, those monitoring the event are now concerned that the entire shelf, after shedding more than 12% of its area, could follow the fate of its more northern peers, Larsens A and B, which collapsed entirely in 1995 and 2002, respectively.

The calving occurred sometime between Monday and today, said researchers from the MIDAS Project, a team of U.K. researchers who have been assiduously monitoring the ice shelf for several years. They’ve watched as the previously stable Larsen C thinned and developed cracks. In 2013, one crack in particular managed to slash through the shelf's “suture zones,” irregularly patterned regions, formed by inflows of ice from land, that tend to prevent rifts from traveling through them. This past year, the zigs and zags of the rift accelerated rapidly. “We have been anticipating this event for months, and have been surprised how long it took for the rift to break through the final few kilometers of ice,” said Adrian Luckman, a glaciologist at Swansea University in the United Kingdom and the project’s lead investigator.

It’s the glaciological equivalent of reality TV.

Daniel McGrath, University of Colorado

It’s far from certain that Larsen C will collapse in the wake of this loss. The stresses from birthing the iceberg could contribute to a collapse, or the newly exposed face of the shelf could be more susceptible to calving. It will be particularly important to watch whether a number of dormant cracks, all currently stalled by suture zones, are revived by the collapse, says Chris Borstad, a glaciologist at the University Centre in Svalbard, Norway. “If any of these begins to grow, they could be much more problematic to the stability of the shelf.” It’s also possible, other researchers say, that the new iceberg may constitute “passive” ice that Larsen C can shed without further loss, and the shelf may remain stable, begin adding new ice, and persist for decades.

But if the shelf does disappear, it would remove a buttress that has prevented land-grounded glaciers from sliding into Antarctic waters. Losing that barrier and unleashing the glaciers would on its own raise global sea levels by a few millimeters, scientists say—nearly equaling the rise the world typically sees each year because of climate change.

As the Larsen C crack progressed this past year, it has received a vast amount of press attention. “It’s the glaciological equivalent of reality TV,” says Daniel McGrath, a glaciologist at the University of Colorado in Boulder.

Off the shelf

An iceberg the size of Delaware has broken off the Larsen C Ice Shelf.

Credits: (Graphic) J. You/Science; (Data) Project MIDAS

The attention also exposed a debate among glaciologists about how climate change affected the iceberg’s development. The dynamics of calving are complex, and no causal link has been established between warming air and water and the expansion of the crack: Did they change the ice’s internal stress? Did they weaken the suture zone? Did they not influence it at all? It’s hard to say. But it’s no stretch to say the calving is part of a larger trend driven by human-caused climate change, Borstad says. “Even if we cannot say for certain whether a single crack and a single iceberg are related to climate change, we should expect that an ice shelf subjected to warming and thinning would retreat and eventually collapse.”

Whenever Larsen C does collapse, be it soon or decades from now, the new iceberg serves as a sign that the instability of the ice sheets is progressing south toward the body of Antarctica, where vast stores of land-bound water—meters, not millimeters of sea level rise—are similarly buttressed by ice shelves. “As climate warming advances farther south,” added Eric Rignot, a glaciologist at the University of California, Irvine, in a statement, “it will affect larger and larger ice shelves that currently hold back bigger and bigger glaciers, so their collapse will contribute more to sea level rise.”

It's there that the future of sea level rise, and cities across the world, will play out.

*Correction, 13 July, 4 p.m.: An earlier caption misstated the date of the image.