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Evidence from a 2,000-foot-long ice core reveals that the West Antarctic Ice Sheet shrank suddenly and dramatically about 8,000 years ago, according to new research — providing alarming insight into how quickly Antarctic ice can melt and cause sea levels to rise.

At the end of the last ice age, part of the ice sheet thinned by 450 meters (1,476 feet) in just 200 years — more than the Empire State Building — according to a study published Wednesday in the journal Nature Geoscience. .

According to the study authors, this is the first direct evidence showing such rapid ice loss anywhere in Antarctica.

While scientists knew the ice sheet was larger at the end of the last ice age than it is today, much less was known about exactly when that shrinkage occurred, said Eric Wolff, a glaciologist at the University of Cambridge in the United Kingdom and author of the study.

This study changes that, he told CNN. “We were able to tell exactly when it retreated, but we could also tell how quickly it retreated.”

It is now clear that the ice sheet retreated and thinned very quickly in the past, Wolff said, and the danger is that it could start again. “If he starts to back off, he will do so very quickly indeed,” he added.

This could have catastrophic consequences for global sea level rise. The West Antarctic Ice Sheet holds enough water to raise sea levels by about 5 meters — more than 16 feet — which would cause devastating flooding in coastal towns and cities around the world.

The study is “a great piece of detective work” on a larger portion of the Antarctic ice sheet, said Ted Scambos, a glaciologist at the University of Colorado Boulder.

Inside the drilling tent on the Ice Rise Skytrain, scientists prepare the drill for the next drop into the well. (University of Cambridge/British Antarctic Survey)

The key message is that “the amount of ice stored in Antarctica can change very quickly — at a rate that many coastal cities would struggle to cope with,” he told CNN.

Ice cores are a historical archive of the Earth’s atmosphere. Made up of layers of ice that formed as snow fell and compacted over millennia, they contain bubbles of ancient air and pollutants that provide a record of environmental change over millennia.

The ice core analyzed in the study was drilled from the Skytrain Ice Rise, which is located at the edge of the ice sheet, near the point where the ice begins to float and become part of the Ronne Ice Shelf.

Scientists obtained it in 2019 in a painstaking process that involved drilling continuously for 40 days, lifting a thin cylinder of ice a few meters at a time. The core was then cut into sections, packed in insulated boxes kept at minus 20 degrees Celsius and sent by plane to the UK and then by ship.

Once in the UK, scientists measured the water isotopes of the ice core, which provide information about the temperature in the past. Warmer temperatures indicate lower-lying ice — think of it like a mountain, Wolff said, the higher you go, the colder it gets.

They also measured the pressure of trapped air bubbles in the ice. Lower and thinner ice contains air bubbles with higher pressure.

It was a surprise when the data revealed how quickly the ice thinned at the end of the last ice age, Wolff said. “We actually spent a lot of time checking to see if we made a mistake with the analysis.”

The West Antarctic Ice Sheet is particularly vulnerable to climate change because the land is below sea level and is subsiding. When the warm water gets below, it can melt very quickly. “It can have a runaway process, and that apparently happened 8,000 years ago,” Wolff said.

Insulated boxes full of ice cores being loaded into the Twin Otter, Skytrain Ice Rise, Antarctica. (Eric Wolff)

What makes the findings so troubling, said Isobel Rowell, an ice core scientist at the British Antarctic Survey and co-author of the study, is that once this escape occurs, “we can do very little, if anything, to stop it,” she told CNN.

The key thing “is not to test it too far,” Wolff said, which means dealing with climate change. “We can still avoid those tipping points,” he said.

The new data will help improve the accuracy of the models scientists use to predict how the ice sheet will respond to future global warming, the report says.

David Thornalley, an ocean and climate scientist at University College London, said the study’s data were “staggering”. He noted that since the study looked at a period 8,000 years ago when climate conditions were different, the results are not a direct example of what might happen today. But he added that they could still offer “insight into the way ice sheets can collapse.”

The study comes as scientists continue to sound the alarm about what is happening to Earth’s most isolated continent.

For example, the Thwaites Glacier, also in West Antarctica, is melting rapidly. A 2022 study found that Thwaites – dubbed the Doomsday Glacier because of the catastrophic impact its collapse would have on sea level rise – is holding on “by its fingernails” as the planet warms.

This new study adds to those concerns, Scambos said. “(It) shows that the same processes that we’re seeing just now in areas like Thwaites Glacier were taking place earlier in similar areas of Antarctica, and in fact the rate of ice loss was on par with our worst fears of runaway ice. loss.”

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