August 12, 2022 STEVE GORMAN
Los Angeles, USA Reuters
Antarctica’s coastal glaciers are shedding icebergs faster than nature can replenish the melting ice, doubling previous estimates of losses from the world’s largest ice sheet over the past 25 years, a satellite analysis.
The first-of-its-kind study, led by researchers at NASA’s Jet Propulsion Laboratory near Los Angeles and published in the journal Nature, raises new concerns about how quickly climate change is weakening the floating ice shelves of Antarctica and accelerating global sea level rise. .
An aerial view of the 60-meter-high front of the cracked Getz Ice Shelf, Antarctica, in this undated handout image. PHOTO: NASA/Handout via Reuters.
The study’s key finding was that the net loss of Antarctic ice from pieces of coastal glaciers that “break 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 the melting of the ice shelves. from below due to the warming of the seas.
Together, thinning and calving have reduced the mass of the Antarctic ice shelves by 12 trillion tons since 1997, double the previous estimate, the analysis concluded.
The net loss of the continent’s ice sheet over the past quarter-century alone spans nearly 37,000 square kilometers, an area nearly the size of Switzerland, according to JPL scientist Chad Greene, lead author of the study.
“Antarctica is collapsing at its edges,” Greene said in a NASA announcement about the findings. “And when the ice shelves shrink and weaken, the continent’s massive glaciers tend to accelerate and increase the rate of global sea level rise.”
The consequences can be huge. 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 slide easily into the ocean, causing the seas to rise.
When ice shelves are stable, the long-term natural cycle of calving and regrowth keeps their size fairly constant.
In recent decades, however, warming oceans have weakened the shelves from below, a phenomenon previously documented by satellite altimeters that measured the changing height of the ice and showed losses averaging 149 million tons per year since from 2002 to 2020, according to NASA.
Space imagery For their analysis, Greene’s team synthesized satellite imagery from visible, thermal infrared and radar wavelengths to more precisely map glacial flow and calving since 1997 than ever more than 50,000 kilometers of Antarctic coast.
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Losses measured from calving outstripped the replenishment of the natural ice shelf so much that researchers found it unlikely that Antarctica could return to pre-2000 glacier levels by the end of this century.
Accelerated glaciation, like thinning ice, 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 losses than gains,” Greene said.
One event from East Antarctica that shocked the world was the collapse and disintegration of the massive Conger-Glenzer ice shelf in March, possibly a sign of greater weakening, 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 the that may happen in the future.
“The good news is that if we keep to the two degrees of global warming promised by the Paris Agreement, sea level rise due to the East Antarctic Ice Sheet should be modest,” he wrote Wolff in a commentary on the JPL study.
However, if greenhouse gas emissions are not curbed, it risks contributing to “many meters of sea level rise over the next few centuries,” he said.