For decades, the Perito Moreno Glacier in Argentina has looked like an outlier as so many of the world’s other great ice masses melt and waste away.
The glacier’s snout — its mighty leading edge — lengthened and shortened, but not by much, at least by glacial standards. Its surface didn’t thin greatly. In fact, it may have even gotten a little thicker.
All that seems to be changing. The Perito Moreno has been thinning at a sharply accelerated rate since 2019, scientists reported on Thursday. And if the thinning doesn’t slow, it could kick-start a series of changes that might cause the ice to shrink even faster.
“Everything that we can see and know lets us believe that irreversible and large-scale glacier retreat is imminent,” said Moritz Koch, a doctoral student in geography and geosciences at Friedrich-Alexander University of Erlangen-Nuremberg in Germany.
If Mr. Koch and his colleagues’ predictions, published Thursday in the journal Communications Earth & Environment, are borne out, they imply a momentous change of fortune for one of the world’s most beloved glaciers. The Perito Moreno is the centerpiece of Los Glaciares National Park, a UNESCO World Heritage site visited by hundreds of thousands of people every year.
The glacier, a river of craggy ice nearly 20 miles long, pours out of the cloud-swathed southern Andes like a mirage. Tourists gather at its side to watch huge chunks of bluish ice peel off and plunge, with a thunderous splash, into the lake at the glacier’s edge.
Scientists believe a quirk of geography has kept the Perito Moreno from shedding too much mass as the Andes region warms. Because of the shape of the valley in which the glacier sits, the high-elevation area where snow falls and ice forms is large compared with the area lower down, where the ice melts. In other words, ice that’s been lost has historically been amply replenished.
Something else might be holding the glacier steady as well: a ridge of bedrock beneath the ice that pins it in place. But before now, scientists knew little about the size of the ridge and how it interacted with the glacier.
That is why Mr. Koch ended up in a helicopter a few years ago, dangling a 750-pound radar rig above the Perito Moreno’s surface.
By blasting electromagnetic waves into the ice, the radar measured the glacier’s thickness. But its surface is too crevassed to walk or drive on, so Mr. Koch and his colleagues needed to find a helicopter and a willing pilot. They waited weeks for a day that wasn’t too windy. Then they hit the skies.
Mr. Koch felt tense, he said, as he guided the pilot back and forth over the glacier. A year of work had gone into the flight. The success of his team’s project was riding on collecting the data accurately. “It takes a while until you enjoy the flight,” he said.
It took Mr. Koch almost another year to process the data they gathered. What he found astonished him.
His radar soundings showed that the bedrock ridge jutted deeply into the ice at the front of the glacier. This implies that once the ice becomes thin enough, it could be at risk of detaching from the ridge. Without the bedrock to hold it in place, the ice could start to float in the water of the lake, making it even more vulnerable to thinning or breaking apart.
Using satellite measurements of the height of the glacier’s surface, Mr. Koch and his colleagues found that the thinning started speeding up in 2019. What caused this abrupt acceleration is still unclear.
Bethan Davies, a professor of glaciology at Newcastle University in England, advised caution in declaring anything irreversible.
“Often glaciers will grow again, if we make it colder and snowier enough,” said Dr. Davies, who wasn’t involved in Mr. Koch’s study. To do that, though, nations would first need to stop warming the planet by adding carbon dioxide to the atmosphere, Dr. Davies said.
Apart from the Perito Moreno, another prominent glacier once seemed to be resisting a watery, vanishing fate: For half a century, scientists watched the gargantuan Taku Glacier, northeast of Juneau, Alaska, thicken and advance as other ice around it dwindled.
Then, in 2018, following a summer of record heat in Alaska, the Taku began to retreat, joining the tens of thousands of glaciers that the warming climate is pushing toward oblivion.
Raymond Zhong reports on climate and environmental issues for The Times.
The post A Famously Stable Glacier in Argentina Suddenly Looks Anything But appeared first on New York Times.
