Antarctic ice shelf Larsen C risks collapsing due to atmospheric rivers

A new study published on Thursday shows that these “rivers in the sky” – which dump rain and snow when they land – also cause extreme temperatures, surface melting, sea ice dissolution and large ocean swells, which destabilize the ice shelves of the Antarctic Peninsula, a long , slender mountain range pointing north to the tip of South America.

These conditions were observed during the collapse of two of the peninsula’s ice shelves – Larsen A and B – in the summers of 1995 and 2002 respectively. And now that the climate crisis is expected to warm the Earth further, the largest remaining ice shelf, Larsen C, is also in danger. total collapse, the study says.

The authors of the study, published in the journal Nature Communications Earth & Environment, used algorithms, climate models and satellite observations to determine that 60% of the peninsula’s calving events – where an iceberg breaks off an ice shelf or glacier – were triggered by atmospheric rivers between 2000 and 2020.

There are many ways in which these ice shelves can destabilize. For Larsen A, B and C, there have been signs of foehn winds – hot, dry air flowing down a mountain after cool, humid air had risen on the other side. These can cause sudden and dramatic changes in temperatures, and in Antarctica it causes ice melting. It can have contagious effects, including breaking ice shelves – the part of a land-based ice sheet that protrudes beyond seawater.

Melting sea ice also exposes the ice shelves to ocean swells, which can cause further destabilization.

“What our study found was that all of these different aspects are actually caused by atmospheric rivers, especially the intense ones,” one of the study’s lead authors, Jonathan Wille of the Universit√© Grenoble Alpes in France, told CNN.

“And we found that almost all the really extreme temperature events that happen on the Antarctic Peninsula happen with atmospheric rivers.”

What it means for sea level

A collapse of Larsen C would mean bad news for sea levels around the planet.

Ice shelves that break off and can cause sea level rise, but they do not add a large volume – this is because they are already floating in the water. But ice shelves play a crucial role in preventing much larger sea level rises.

“Ice shelves prevent the glaciers that are on land behind them from flowing into the ocean,” Wille said. “And when those shelves disappear, there’s nothing holding back those glaciers. Their velocity increases and begins to float into the ocean. And that then contributes directly to sea level rise.”

Scientists do not yet know what connection there may be between atmospheric rivers and climate change, but the recent heat wave and conditions in Antarctica at the time were so extreme that experts are beginning to assume that the crisis could play a role. It only becomes really clearer if a similar event happens again in the future.

“The question is whether atmospheric rivers will happen more often 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 will,” she said, adding that different atmospheric analyzes yielded different results. “However, it is likely that the atmosphere will play an increasing role in the breakage of the ice shelf by weakening them through surface melting.”

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

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

Atmospheric flood of moisture will trigger storms and tornadoes this week

John Turner, a meteorologist at the British Antarctic Survey who was also not involved in the study, said most of the instability of an ice shelf was due to basal melting – it is melting that happens from the bottom – and warned against putting too much emphasis on whether the role of atmospheric rivers. The study, published in Nature, found no link between atmospheric rivers and basalt melting.

“You have to be careful – you get extremes for other reasons that do not have a river. Sometimes you just get strong northerly direction, which will generally give you a lot of snow and high temperatures, which may not be classified as a river,” he told CNN.

Turner, however, agrees that the wind that atmospheric rivers bring may have been “nailed into the coffin on some of these ice shelves.”

To put into perspective what an ice loss in Antarctica could mean for the world, Turner explained that there are 60 meters – nearly 200 feet – of potential sea level rise if the entire continent’s ice melts. West Antarctica, the wider region around the peninsula, represents a rise of 6 meters (20 feet), which in itself would engulf entire islands and be catastrophic for millions of people living on the coasts and beyond.

Most of the world’s ice melting and sea level rise so far can be attributed to the melting of Greenland’s inland ice in the Arctic.

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