When temperatures in Antarctica rose to 38C above normal in March, an ice shelf the size of Los Angeles collapsed. Scientists don’t know what role extreme temperatures may have played in the event, but the heat has invaded what’s known as an atmospheric river, a long column of moisture that carries warm air and water vapor from the tropics to other parts of the planet.
A new study published Thursday shows that these “flying rivers” — which dump rain and snow when they hit the mainland — are also causing extreme temperatures, surface melt, sea ice disintegration and large ocean waves that are destabilizing. ice shelves on the Antarctic Peninsula, a long, thin mountain range that points north to the tip of South America.
These conditions were observed during the collapse of two ice shelves on the peninsula — Larsen A and B — in the summers of 1995 and 2002, respectively. And now, as the climate crisis is projected to further warm the Earth, the largest remaining ice shelf, Larsen C, is also at risk of 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 peninsula calving events – where an iceberg breaks through an ice shelf or glacier – were triggered by rivers. atmospheric conditions between 2000 and 2020.
There are many ways these ice shelves can destabilize. For Larsen A, B, and C, there is evidence of foehn winds—warm, dry air that descends a mountain after cold, moist air has risen on the other side. This can cause sudden and dramatic changes in temperatures and, in Antarctica, cause ice to melt. This can have indirect effects, including fractures in ice shelves – the portion of a layer of land ice that juts out into ocean water.
Melting sea ice also exposes ice shelves to ocean swell, 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, from Université Grenoble Alpes, France, told CNN.
“And we found that almost all of the really extreme temperature events that happen on the Antarctic Peninsula happen with atmospheric rivers.”
What does it mean for sea level
A collapse of Larsen C would spell bad news for sea levels around the planet.
Ice shelves break up and can cause sea levels to rise, but they don’t add a huge volume – that’s because they’re already floating in the water. But ice shelves play a critical role in preventing a much larger rise in sea levels.
“Ice shelves prevent glaciers that are on land behind them from flowing into the ocean,” Wille said. “And when those platforms disappear, there’s nothing stopping those glaciers. Its speed increases and it begins to flow into the ocean. And that directly contributes to sea level rise.”
Scientists still don’t know what link 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 starting to assume the crisis may be playing a role. This will only really become clearer if a similar event happens again in the future.
Satellite imagery of an atmospheric river over Antarctica on January 25, 2008, which scientists say triggered the disintegration of ice on the Larsen A and Larsen B platforms.
“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 observation and polar modeling at University College London.
“I think it’s too early to say yes,” she said, adding that different atmospheric analyzes were giving different results. “However, the atmosphere is likely to play an increasing role in breaking up ice shelves, weakening them through surface melt.”
While the future frequency of atmospheric rivers may be unknown, Wille believes that, at the very least, they will become more intense, and that could be enough to cause further destabilization.
“It’s kind of simple – as the atmosphere gets warmer, it’s able to hold more moisture, and since an atmospheric river is essentially transporting moisture, that means there’s going to be more moisture that can be transported to Antarctica,” he said. he.
John Turner, a meteorologist with the British Antarctic Survey who was also not involved in the study, said most of the instability of an ice shelf is due to basal melt – which is the melting that happens from the bottom – and cautioned against placing much emphasis on the role of atmospheric rivers. The study published in Nature did not find a link between atmospheric rivers and basal melt.
“You have to be careful—you have extremes for reasons other than having a river. Sometimes you just have strong winds from the north, which usually give you a lot of snow and high temperatures, which might not be classified as a river,” he told CNN.
Turner agrees, however, that the wind that atmospheric rivers bring may be “the nail in the coffin of some of these ice shelves.”
To put into perspective what a loss of ice in Antarctica could mean for the world, Turner explained that there is 60 meters – nearly 200 feet – of potential sea level rise if the ice across the entire continent melts. West Antarctica, the widest region around the peninsula, represents 6 meters of elevation, which alone would engulf entire islands and be catastrophic for millions of people living on the coasts and beyond.
Most of the world’s ice melt and sea level rise so far can be attributed to the melting of the Greenland ice sheet in the Arctic.
Source: CNN Brasil
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