Glaciers off the coast of Antarctica are shedding icebergs faster than nature can replenish the ice, doubling previous estimates of losses from the world’s largest ice shelf over the past 25 years, a satellite analysis showed this week.
The first study of its kind, led by researchers at NASA’s Jet Propulsion Laboratory (LPJ) near Los Angeles and published in the journal Nature, raises new concern about the speed at which climate change is weakening Earth’s floating ice shelves. Antarctica and accelerating the global rise in sea levels.
The main finding of the study was that the loss of chunks from Antarctica’s coastal glaciers that break off into the ocean is nearly equal to the amount of ice that scientists already knew is lost as the lower ice shelves thin out as the sea warms and the melt.
Together, thinning and loosening have reduced the mass of Antarctica’s ice shelves by 12 trillion tonnes since 1997, double the previous estimate, the analysis concluded.
The net loss of the continent’s ice sheet through shedding alone over the past quarter century covers an area of ​​approximately 37,000 square kilometers, about the size of Switzerland, according to LPJ scientist Chad Greene, the study’s lead author.
“Antarctica is crumbling at its edges,” Greene said in a NASA announcement about the findings. “And when ice shelves shrink and weaken, the continent’s massive glaciers tend to accelerate melting and increase the rate of global sea level rise.”
The consequences can be enormous. Antarctica contains 88% of the potential sea level of all the world’s ice, he said.
Ice shelves, permanent floating layers of frozen freshwater tethered to land, take thousands of years to form and act as foothills holding glaciers that would otherwise slide easily into the ocean, causing the seas to rise.
When ice shelves are stable, the natural long-term cycle of shedding and regrowth keeps their size fairly constant.
In recent decades, however, warming oceans have weakened the shelves beneath, a phenomenon previously documented by satellite altimeters that measure the change in ice height and show losses averaging 149 million tonnes a year from 2002 to 2020, according to the NASA.
images from space
For this analysis, Greene’s team synthesized satellite imagery of visible wavelengths, thermal infrared, and radar to map glacial flow and detachment since 1997 with greater accuracy than ever before over 50,000 kilometers off the Antarctic coast.
Measured losses have outstripped the natural replenishment of ice shelves to such an extent that researchers found it unlikely that Antarctica will be able to recover pre-2000 glacier levels by the end of this century.
Accelerated glacial detachment, as well as ice thinning, was most pronounced in West Antarctica, the area hardest hit by warming ocean currents. But even in East Antarctica, a region whose ice shelves were considered less vulnerable, “we’re seeing more losses than gains,” Greene said.
One detachment event in East Antarctica that took the world by surprise was the collapse and disintegration of the massive Conger-Glenzer ice shelf in March, possibly a sign of further weakening in the future, Greene said.
Eric Wolff, a research professor at the Royal Society at the University of Cambridge, pointed to the study’s analysis of how the East Antarctic ice sheet behaved in past warm periods and models of what might happen in the future.
“The good news is that if we maintain the 2 degrees of global warming that the Paris Agreement promises, sea level rise due to the East Antarctic ice shelf should be modest,” Wolff wrote in a commentary on the study by LPJ.
If we fail to limit greenhouse gas emissions, however, there could be “many meters of sea level rise in the next few centuries,” he said.
Translated by Luiz Roberto M. Gonçalves
