A powerful atmospheric river could cause the collapse of the largest ice cap in Antarctica

Watch an Antarctic ice sheet disintegrate 0:51 (CNN) — When temperatures in Antarctica soared to 100 degrees above normal in March, a wobbly ice shelf the size of Los Angeles collapsed. . Scientists don’t know what role extreme temperatures played in the event, but the heat rushed through 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 Earth. the earth. A new study published Thursday shows that these “rivers in the sky,” which dump rain and snow when they make landfall, also cause extreme temperatures, melting of the surface, the disintegration of sea ice and large ocean swells that destabilize the platforms of ice of the Antarctic Peninsula, a long, narrow 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 academic journal Nature Communications Earth & Environment, used algorithms, climate models and satellite observations to determine that 60% of calving events on the peninsula (when an iceberg breaks off an ice shelf or a glacier) were caused by atmospheric rivers between 2000 and 2020. An image of the Larsen B Ice Shelf on the Antarctic Peninsula in 2000, before its collapse in 2002. These ice shelves can become destabilized in many ways. In the case of Larsen A, B, and C, there is evidence of foehn winds, which refers to warm, dry air moving down a mountain after cool, moist air has risen up the other side. This can cause sudden and severe changes in temperatures, and in Antarctica, it causes the ice to melt. This can have indirect effects, such as the fracturing of ice shelves, the part of a land ice sheet that protrudes above ocean water. Melting sea ice also exposes ice shelves to ocean surge, which can cause further destabilization. “What our study found was that all these different aspects are actually caused by atmospheric rivers, especially the intense ones,” Jonathan Wille of Grenoble Alpes University, France, one of the study’s lead authors, told CNN. “And we found that almost all of the really extreme temperature events that happen on the Antarctic Peninsula occur with atmospheric rivers.” What it means for sea levels A collapse of Larsen C would spell bad news for sea levels across the planet. Ice caps break off and can cause sea level rise, but they don’t add a lot of volume, because they’re already floating on the water. However, they play a critical role in preventing a much larger rise in sea level. “The ice caps prevent the glaciers that are on the mainland behind them from flowing into the ocean,” explains Wille. “And when these shelves disappear, there’s nothing to hold those glaciers back. Their speed increases and they start flowing out into the ocean. And that directly contributes to sea level rise.” Scientists still don’t know what relationship 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 hypothesize that the crisis could be playing a role. This will only really become clear if a similar event is repeated in the future. Satellite images of an atmospheric river over Antarctica on January 25, 2008, which scientists say triggered the breakup of ice in the Larsen A and Larsen B ice caps. “The question is whether atmospheric rivers will occur more frequently as change the climate,” Julienne Stroeve told CNN. Stroeve, who was not involved in Thursday’s study, is a professor of polar observing and modeling at University College London. “I think it’s too early to say that she will,” she said, adding that different atmospheric analyzes were giving different results. “However, the atmosphere is likely to play an increasingly important role in breaking up ice caps by weakening them through surface melting.” Although the future frequency of atmospheric rivers may be unknown, Wille believes that they will, at a minimum, become more intense, and that could be enough to cause further destabilization. “It’s pretty straightforward: as the atmosphere warms, it’s able to hold more moisture, and since an atmospheric river is essentially transporting moisture, that means there will be more moisture that can be transported to Antarctica,” she said. John Turner, a meteorologist with the British Antarctic Survey who was also not involved in the study, said that most of the instability of an ice cap is due to basal melting, that is, melting from the bottom, and cautioned that the role of atmospheric rivers should not be overemphasized. The study published in Nature found no relationship between atmospheric rivers and basal melting. The Larsen C Ice Shelf on October 31, 2017, after a massive iceberg broke off of it. “You have to be careful: extremes occur for reasons other than a river [atmosférico]. Sometimes you just get strong northerly winds, which usually produce a lot of snow and high temperatures, which may not be classified as a river,” he told CNN. However, Turner agrees that the wind they bring atmospheric rivers may be “the nail in the coffin for some of these ice shelves.”To put into perspective what a loss of ice from Antarctica could mean for the world, Turner explained that there is 60 meters of potential sea level rise of the sea if all the ice on the continent melted West Antarctica, the wider region surrounding the peninsula, represents an increase of 6 meters, which would swallow entire islands in the first place and be catastrophic for millions of people living in the coasts and beyond Most of the global melting and sea level rise so far can be attributed to the melting of the Greenland ice sheet in the Arctic.