Antarctic ice shelf Larsen C is at risk of collapse due to atmospheric rivers

A new study published on Thursday shows that the “river in the sky” – those that pour rain and snow as they make landfall – also cause extreme heat, surface melt, sea ice disintegration and large ocean waves that are destabilizing the ice shelves on the Southern Peninsula The Pole, a long, spiky chain of mountains toward the northern tip of South America.

These conditions were observed during the collapse of two ice shelves on the peninsula – Larsen A and B – in the summer of 1995 and 2002 respectively. And now, as the climate crisis is projected to unfold. warming the Earth even further, the largest remaining ice shelf, Larsen C, is also at risk of total collapse, the study said.

The authors of the study, published in Nature Magazine Earth & Environment Communicationused algorithms, climate models and satellite observations to determine that 60% of peninsular spawning events – where an iceberg breaks off an ice shelf or glacier – are triggered by rivers in the atmosphere between 2000 and 2020.

There are many ways these ice sheets can be destabilizing. For Larsen A, B, and C, there was evidence of foehn winds – warm, dry air that swept down a mountain after cool, moist air had already ascended the other side. These can cause sudden and drastic temperature changes, and in Antarctica, it causes the ice to melt. That can have dramatic effects, including fracturing ice shelves – the part of land ice that sticks out above ocean water.

Melting sea ice also causes ice shelves to swell, which can add to the instability.

One of the study’s lead authors, Jonathan Wille from the University of Grenoble Alpes in France, told CNN: “What our study found is that all these different aspects are actually caused by the atmospheric rivers, especially those caused by high intensity.

“And we found that almost all of the really extreme temperature events happen in the Antarctic Peninsula, which happens with atmospheric rivers.”

What it means for sea level

The collapse of Larsen C will spell bad news for sea levels around the planet.

Ice shelves break off and can cause sea levels to rise, but they don’t add much mass – that’s because they’re already floating in the water. But ice shelves play an important role in preventing a much larger rise in sea levels.

“Ice shelves prevent land-based glaciers from flowing into the ocean,” said Wille. “And when these prices go away, there’s nothing that can stop those glaciers. Their velocity increases and starts to flow into the ocean. And that then directly contributes to sea level rise. .”

Scientists still don’t know if there is a link between atmospheric rivers and climate change, but the recent heatwave and conditions in Antarctica at the time were so extreme that experts began hypothesized that the crisis might play a role. That will only really become clearer if a similar event occurs again in the future.

Satellite image from an atmospheric river over Antarctica on January 25, 2008, which scientists believe triggered the breakup of ice in the Larsen A and Larsen B shelves.

“The question is whether atmospheric rivers are occurring more frequently as the climate changes,” Julienne Stroeve told CNN. Stroeve, who was not involved in Thursday’s study, is a professor of polar observation and modeling at University College London.

“I think it’s too early to say it’s going to happen,” she said, adding that different atmospheric analyzes are giving different results. “However, it is likely that the atmosphere will play an increasing role in the breaking of ice shelves by weakening them due to surface melting.”

While the frequency of future atmospheric rivers may be unknown, Wille believes they will at least become more intense, and that could be enough to cause more instability.

“It’s pretty simple – as the atmosphere gets warmer, it can hold more moisture, and since an atmospheric river is essentially transporting moisture, that means,” he said. there will be more moisture that can be transported to Antarctica.

Atmospheric moist river will cause storms and tornadoes this week

John Turner, a meteorologist at the British Antarctic Survey who was also not involved in the study, says that much of the ice shelf instability is due to fundamental melting – that is, the melting of the ice shelf. runoff occurs from the bottom – and cautions against overemphasizing the role rivers play in the atmosphere. The study, published in the journal Nature, found no link between atmospheric rivers and underlying melting.

“You have to be careful – you can get extremes for other reasons without rivers. Sometimes you just get strong northerly winds, which will usually bring you lots of snow and high temperatures, which may not be classified. is the river,” he told CNN.

However, Turner agrees that the winds brought by atmospheric rivers could be “the nail in the coffin of some of these ice shelves.”

To give perspective on what the loss of Antarctica’s ice could mean for the world, Turner explained that there is a potential for sea level rise of 60 meters – almost 200 feet if the entire continent were to melt. . West Antarctica, the larger area around the peninsula, is 6 meters (20 feet) high, which in itself would swallow entire islands and be a disaster for millions of people living on the coasts and beyond. again.

Much of the world’s ice melt and sea level rise to date can be attributed to the melting of the Greenland ice sheet in the Arctic.

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