How Concerned Should We Be About This Massive Crack in Antarctica?

The Larsen C crack, photographed from the air on Nov. 10, 2016. John Sonntag/NASA The Larsen C crack, photographed from the air on Nov. 10, 2016. John Sonntag/NASA
The Larsen C crack, photographed from the air on Nov. 10, 2016. John Sonntag/NASA

Forget about Donald Trump's latest Twitter feud for a moment. A vastly bigger rift has developed down near the bottom of the world, in western Antarctica's Larsen C ice shelf — the fourth largest on the frozen continent.

Scientists from Great Britain's MIDAS Project have been monitoring recent acceleration in the growth of a giant crack in the ice. It stretches more than 70 miles (112.7 kilometers) and is more than 300 feet (91.4 meters) wide and a third of a mile (half a kilometer) deep. They say the crack now only has about 12 miles (19.3 kilometers) more to go before it reaches the shelf's edge and fractures the ice. When that happens, the ice shelf will lose about 10 percent of its area, and a 1,930-square-mile (5,000-square-meter) iceberg — bigger than the state of Rhode Island — will break off and drift into the Southern Ocean.

MIDAS project leader Adrian Luckman, a professor at Swansea University, expects the calving most likely will occur in the next few months. He writes in an email interview that prediction is based upon the rate at which the crack is widening, plus "the fact that there is now only 20 kilometers (12 miles) of ice left to break through."

What does this all mean for the rest of the planet? Unfortunately, it's hard to say.

According to the British Antarctic Survey, which works with MIDAS, scientists don't really know whether the crack in Larsen C has anything to do with climate change, although there is some evidence that the ice shelf has become thinner because of it.

"I doubt it will ever be possible to link this rift to climate change," says Luckman. "What we CAN say is that ice-shelves seem in general to be responding to a warmer climate. For Larsen C, all I would say is that climate warming (ocean or atmosphere) cannot be directly linked to the rift, but probably won't have hindered its growth."

It's normal for cracks to form in ice shelves and calve to produce icebergs, as part of a cyclical process in which the shelves, fed by glaciers and ice streams from the continent's interior, gradually advance, break and then slowly regenerate.

"Calving from all Antarctic ice shelves occurs periodically," H. Jay Zwally, a senior research scientist at NASA, explains via email. "Some calving is in small icebergs and less frequently is in large tabular icebergs as the one about to calve from Larsen C. This calving occurs to balance the continuous flow of ice into the shelves over the grounding line — i.e. the ground ice sheet on upstream side and floating ice shelf on the ocean-ward side."  

He notes that such calving "occurs at decadal intervals without climate change to make it happen."

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The crack in the Larsen C ice shelf has grown at a surprisingly rapid pace recently.
John Sonntag/NASA

Larsen C's crack has grown with unusual speed — 18 miles (29 kilometers) in the past month alone — and to some, that's a sign of potential trouble ahead. As NASA's Earth Observatory website notes, big calving events led to the sudden near-total disintegration of Larsen B, an ice shelf that broke up and collapsed in the course of a single month in 2002. Back in 2015, MIDAS scientists published a paper in which they concluded that Larsen C faced a "significant risk" of becoming unstable.

Luckman says the calving will remove a "'passive' part of the ice shelf" —one that doesn't contribute  to holding back the glaciers — "so it may be quite benign," he says. "However, the remaining shelf will no longer have this buffer of passive ice, and very little passive ice will be left, so it will be more vulnerable and therefore less stable and at considerable risk of further calving down the line, a timescale on which we would not like to speculate."

According to Scientific American, if Larsen C did break up, as the Larsen B shelf did before it, one scenario is that Antarctic glaciers no longer restrained by the ice shelf would speed their flow of ice into the ocean. In a hypothetical scenario in which all the ice that Larsen C holds back was released, that potentially could cause global sea levels to rise by as much as 4 inches (10.2 centimeters), according to BBC News.

But not everyone thinks that is likely to happen. In this 2016 study published in Nature Climate Change, European scientists concluded even calving of a vast iceberg from Larsen C "will be unlikely to produce much dynamic change."

Ted Scambos, a senior research scientist for the National Snow and Ice Data Center, who is headed to Antarctica to study the crack, told the Associated Press that the calving wouldn't trigger a quick disintegration of the ice shelf.

Similarly, NASA's Zwally doesn't see the crack in Larsen C as cause for immediate alarm. "There is a risk of the ice shelf collapse," he says. "But the calving of this large iceberg is not a sign that collapse is imminent."