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The rapid collapses of two ice shelves on the Antarctic Peninsula over the past quarter century were likely triggered by the arrival of huge plumes of warm, moisture-laden air that created extreme conditions and destabilized the ice, researchers said on Thursday.

Before the rupture of the Larsen A shelf in 1995 and the Larsen B shelf in 2002, landfall of these clouds, called atmospheric rivers, took place from the Pacific Ocean. Over a few days, they produced extremely hot temperatures, which caused the ice to break up causing surface melting and reduced sea ice cover, allowing ocean swell to stretch and further weaken the ice shelves.

“We define atmospheric rivers as a mechanism that can create extreme conditions on the ice shelves of the Antarctic Peninsula and potentially lead to its destabilization,” said Jonathan Wille, a climatologist and meteorologist at the Université Grenoble Alpes in France. work describing research In the journal Communications Earth and Environment.

Although there has been no subsidence on the peninsula since 2002, Dr. Wille and colleagues found that atmospheric rivers triggered 13 of 21 major iceberg calving events from 2000 to 2020.

Dr. The larger Larsen C shelf, which is still largely intact and is the fourth largest ice shelf in Antarctica with an area of ​​approximately 17,000 square miles, could eventually meet the same fate as A and B, Wille said.

“The only reason the melt hasn’t been significant so far is because it’s farther south than the others, and therefore colder,” he said. But as the world continues to warm, atmospheric rivers are expected to become denser. “Larsen C will now be at risk from the same processes,” he said.

Kyle R. Clem, a researcher at Victoria University of Wellington in New Zealand who was not involved in the study, said the study shows that other parts of Antarctica that are not warming as quickly as the peninsula may ultimately be susceptible as well. The mechanism the researchers documented is largely due to warming where the atmospheric river originates.

Dr. “The amount of heat and moisture carried by atmospheric rivers is higher than it would be without global warming,” Clem said. “So the air mass hitting Antarctica is much, much hotter. And these are episodes of extreme events that led to the ice shelf collapsing.”

“You can get this anywhere in Antarctica,” he said.

Shelves are tongues of floating ice that hold most of the ice that covers Antarctica to a depth of about 3 miles. When a shelf collapses, the flow of this land ice into the ocean accelerates, increasing the rate of sea level rise.

While the Antarctic Peninsula ice sheet is relatively small (if it all melted, seas would rise less than a meter), collapse of ice shelves elsewhere on the continent could cause sea level to rise much more over the centuries.

Last month, A small ice shelf collapsed in East AntarcticaIt is considered the most stable part of the continent. An intense atmospheric river had come to the area in the previous days. It did record high temperatures, but researchers aren’t yet sure what role, if any, role it played in breaking up the shelf.

Atmospheric rivers occur when a large region of constant high pressure air encounters a low pressure storm system. A narrow stream of moist air flows from the junction of the two.

In a typical Southern Hemisphere summer, the peninsula receives one to five of these events, the researchers said. They only looked at those with the highest volume of water vapor.

If a river is dense enough, it can cause several days of surface melting of the ice shelf. As the melt water flows into the crevices, it refreezes, widening and widening the cracks. Eventually, such repeated hydrofracturing, called the process, can cause the ice shelf to break apart.

Atmospheric river can also speed up the process by melting sea ice or by associated winds pushing the sea ice away from the shelf. This allows the ocean waves to shake the ice shelf and accentuate it even more.

Some large ice shelves in West Antarctica are thinning as warm ocean water melts from below. Regardless of long-term warming and thinning trends, this article raises the important point that very brief weather events can push. An ice shelf past the tipping point.”