Satellite images show the Antarctic ice shelf is crumbling faster than previously thought

By Steve Gorman

LOS ANGELES (Reuters) – Antarctica’s coastal glaciers are shedding icebergs faster than nature can replenish the crumbling ice, doubling previous estimates of losses from the world’s largest ice sheet in the past 25 years. , a satellite analysis showed on Wednesday.

The first study of its kind, led by researchers at NASA’s Jet Propulsion Laboratory (JPL) near Los Angeles and published in the journal Nature, raises new concerns about how quickly climate change is weakening floating ice from Antarctica and accelerating the rise in global sea levels.

The key finding of the study was that the net loss of Antarctic ice from coastal glacial chunks “breaking off” into the ocean is almost as great as the net amount of ice that scientists already knew was being lost due to the thinning caused by melting ice shelves. from below by warming seas.

Together, thinning and calving have reduced the mass of Antarctica’s ice shelves by 12 billion tons since 1997, double the previous estimate, the analysis concluded.

The net loss of the continent’s ice sheet from calving alone in the last quarter century spans nearly 37,000 square kilometers (14,300 square miles), an area nearly the size of Switzerland, according to JPL scientist Chad Greene, lead author of the study. study.

“Antarctica is falling apart,” Greene said in a NASA announcement about the findings. “And when ice shelves shrink and weaken, the continent’s massive glaciers tend to accelerate and increase the rate of global sea level rise.”

The consequences could be huge. Antarctica has 88% of the sea level potential of all the world’s ice, she said.

Ice shelves, permanent floating sheets of frozen freshwater attached to the land, take thousands of years to form and act as buttresses holding back glaciers that would otherwise slide easily into the ocean, causing the rise of the seas.

When ice shelves are stable, the natural long-term cycle of calving and regrowth keeps their size fairly constant.

However, in recent decades, warming oceans have weakened the shelves from below, a phenomenon previously documented by satellite altimeters that measure the changing height of the ice and show average losses of 149 million tons a year between 2002 and 2020. according to NASA.

IMAGES FROM SPACE

For their analysis, Greene’s team synthesized satellite images of visible, thermal and infrared wavelengths, and radar to map glacial flow and calving since 1997 more accurately than ever before for 30,000 miles (50,000 km) of the coastline. Antarctica.

Measured losses from calving so far outstripped replenishment of the natural ice shelf that the researchers found it unlikely that Antarctica could return to pre-2000 glacial levels by the end of this century.

Accelerated glacial calving, like ice thinning, was most pronounced in West Antarctica, an area most affected by warming ocean currents. But even in East Antarctica, a region whose ice shelves were long considered less vulnerable, “we’re seeing more loss than gain,” Greene said.

One East Antarctic calving event that took the world by surprise was the collapse and disintegration of the huge Conger-Glenzer ice shelf in March, possibly a sign of further weakening to come, Greene said.

Eric Wolff, Royal Society Research Professor at the University of Cambridge, pointed to the study’s analysis of how the East Antarctic Ice Sheet behaved during past warm periods and models of what may happen in the future. .

“The good news is that if we maintain the 2 degrees of global warming promised by the Paris agreement, sea level rise from the East Antarctic Ice Sheet should be modest,” Wolff wrote in a commentary on the study. from JPL.

However, if greenhouse gas emissions are not reduced, they risk contributing “many meters of sea level rise in the coming centuries,” he said.

(Reporting by Steve Gorman in Los Angeles; Editing by Tom Hogue)

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