Satellite images show Antarctic ice shelves collapsing faster than thought

LOS ANGELES, Aug 10 (Reuters) – Glaciers off Antarctica’s coast are shedding faster than nature is replenishing the collapsing ice, satellite analysis showed on Wednesday, pushing estimates of the world’s largest ice sheet loss over the past 25 years. doubled.

Led by researchers at NASA’s Jet Propulsion Laboratory (JPL) near Los Angeles and published in the journal Nature, the first-of-its-kind study has sparked new understanding of how climate change is rapidly weakening Antarctica’s floating ice shelves and accelerating their rise. worry. Global sea level.

The study’s main finding is that the net loss of Antarctic ice from the “disintegration” of coastal glaciers into the ocean due to thinning due to melting ice shelves is almost as large as the net loss of ice that scientists already know from below through the warming ocean .

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Thinning and disintegration have reduced the mass of Antarctica’s ice shelves by 12 trillion tons since 1997, double previous estimates, the analysis concluded.

In the past 25 years alone, the net loss of the continent’s ice sheet has spanned nearly 37,000 square kilometers (14,300 square miles), nearly the size of Switzerland, said lead author of the study, Jet Propulsion Laboratory scientist Chad Green. .

“Antarctica is collapsing,” Green said in the findings released by NASA. “As ice shelves shrink and weaken, the continent’s huge glaciers tend to accelerate and accelerate the rate of global sea level rise.”

The consequences could be huge. Antarctica holds 88% of the sea level potential of all ice sheets in the world, he said.

Ice shelves are permanently floating sheets of frozen freshwater attached to land that take thousands of years to form and act like support glaciers that hold back glaciers that would otherwise easily slip into the ocean, causing sea level rise.

When the ice shelf is stable, the long-term natural cycle of calving and regrowth keeps its size fairly constant.

In recent decades, however, warming oceans have weakened ice shelves from below, a phenomenon previously recorded by satellite altimeters, which measure changes in the height of the ice, and show that from 2002 to 2020, the average 149 million tons are lost every year.

images from space

For the analysis, Greene’s team synthesized satellite imagery from visible, thermal infrared and radar wavelengths to map more than 30,000 miles (50,000 kilometers) of Antarctic coastline since 1997 more accurately than ever before.

The losses measured by calving have so far outpaced natural ice shelf replenishment that researchers found that Antarctica is unlikely to return to pre-2000 glacial levels by the end of the century.

Accelerated glacier collapse, like ice thinning, is most pronounced in West Antarctica, a region hit harder by warming ocean currents. But even in East Antarctica, an area of ​​the ice shelf long considered less vulnerable, “we’re seeing more losses than gains,” Green said.

One East Antarctic calving event that took the world by surprise, Green said, was the collapse and disintegration of the massive Conger-Glenzer Ice Shelf in March, which could be a sign of greater weakening in the future.

Eric Wolff, a research professor at the Royal Society at the University of Cambridge, said the study analysed models of how the East Antarctic ice sheet has behaved during past warm periods and what might happen in the future.

“The good news is that sea level rise from the East Antarctic ice sheet should be modest if we maintain the 2 degrees of global warming promised by the Paris Agreement,” Wolf wrote in a commentary to the JPL study.

However, failure to curb greenhouse gas emissions could lead to “several meters of sea level rise over the next few centuries,” he said.

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Reporting by Steve Gorman in Los Angeles; Editing by Tom Hogg

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