Satellite imagery shows Antarctic sea ice is collapsing faster than expected
Antarctica’s coastal glaciers are shedding icebergs faster than nature can replenish crumbling ice, doubling previous estimates of losses from the world’s largest ice sheet in the past 25 years, a researcher revealed on Wednesday. satellite analysis.
The first-of-its-kind study, conducted 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 the platforms of floating ice of Antarctica and accelerating the rise of global sea levels.
The main conclusion of the study was that the net loss of Antarctic ice due to pieces of coastal glaciers “calving” into the ocean is almost as large as the net amount of ice that scientists already knew was lost due to thinning caused by melting ice shelves. from below by the warming of the seas.
Taken together, thinning and calving have reduced the mass of Antarctic ice shelves by 12 trillion tonnes since 1997, double the previous estimate, the analysis concluded.
The net loss of the continent’s ice sheet from calving alone over the past quarter-century spans almost 37,000 km2 (14,300 square miles), an area nearly the size of Switzerland, according to the scientist from the JPL 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 could be enormous. Antarctica holds 88% of the sea level potential of all ice in the world, he said.
Ice shelves, permanent floating sheets of frozen fresh water attached to land, take thousands of years to form and act as buttresses holding back glaciers that would otherwise slide easily into the ocean, causing rising seas.
When ice shelves are stable, the natural long-term 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 measuring changes in ice height and showing average losses of 149 million tonnes per year. from 2002 to 2020, according to NASA.
For their analysis, Greene’s team synthesized satellite imagery from visible, thermal infrared and radar wavelengths to map ice flow and calving since 1997 more accurately than ever over 30,000 miles (50,000 km) of Antarctic coastline.
Losses measured from calving have exceeded natural sea ice replenishment so much that the researchers found Antarctica unlikely to return to pre-2000 glacier levels by the end of this century.
Accelerated glacial calving, like ice thinning, has been most pronounced in West Antarctica, an area hardest hit by warming ocean currents. But even in East Antarctica, a region whose sea ice has long been considered less vulnerable, “we’re seeing more losses than gains,” Greene said.
An East Antarctic calving event that took the world by surprise was the collapse and disintegration of the massive Conger-Glenzer Ice Shelf in March, possibly a sign of a bigger weakening ahead, Greene said.
Eric Wolff, Royal Society Research Professor at the University of Cambridge, highlighted the study’s analysis of the behavior of the East Antarctic ice sheet during past warm periods and the patterns of what could 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 from the East Antarctic Ice Sheet is expected to be modest,” wrote Wolff in a comment on the JPL study.
Failure to reduce greenhouse gas emissions, however, would risk contributing “many meters to sea level rise over the next few centuries”, he said.