Satellite images show the Antarctic ice shelf crumbling faster than 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 over the past 25 years, a satellite analysis showed on Wednesday.

The first-of-its-kind study, led by scientists 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 Antarctica’s floating ice shelves and accelerating the rise of global sea levels.

The study’s key finding was that the net loss of Antarctic ice from pieces of coastal ice that “calve” into the ocean is almost as great as the net amount of ice that scientists already knew was being lost due to thinning caused by melting of the ice shelves from below by warming oceans.

Combined, thinning and calving have reduced the mass of the Antarctic ice shelf by 12 trillion tonnes since 1997, double previous estimates, the analysis concluded.

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

“Antarctica is crumbling at the edges,” Greene said in a NASA announcement about the findings. “And as the ice shelves shrink and weaken, the continent’s massive glaciers tend to speed up and speed up global sea-level rise.”

The consequences can be enormous. Antarctica has 88% of the sea level potential of all the world’s ice, he said.

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

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

In recent decades, however, warming oceans have weakened the shelves from below, a phenomenon previously documented by satellite altimeters that measure the ice’s changing height and show a loss of an average of 149 million tons a year from 2002 to 2020, according to NASA.

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For their analysis, Greene’s team synthesized satellite images from visible, thermal-infrared and radar wavelengths to map glacier flow and calving since 1997 more precisely than ever over 50,000 km of the Antarctic coastline.

Losses measured from calving outpaced natural ice shelf replenishment so much that scientists found it unlikely that Antarctica could return to pre-2000 glaciation levels by the end of this century.

The accelerated calving, like the thinning of ice, was most pronounced in West Antarctica, an area hit harder by warm ocean currents. But even in East Antarctica, a region whose ice shelves were long considered less vulnerable, “we’re seeing more losses than gains,” Greene said.

One calving event in East Antarctica that surprised the world was the collapse and breakup of the massive Conger-Glenzer ice shelf in March, possibly a sign of a larger weakening to come, Greene said.

Eric Wolff, a Royal Society research professor at the University of Cambridge, pointed to the study’s analysis of how the East Antarctic ice sheet behaved during warm periods from the past and models for what might happen in the future.

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

Failure to curb greenhouse gas emissions, however, risks contributing to “many meters of sea level rise over the next few centuries,” he said.

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

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