Antarctica‘s coastal glaciers are shedding glaciers 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. A first-of-its-kind study 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 Antarctica’s floating ice shelves and accelerating global sea level rise.
A key finding of the study was that the net of Antarctic ice from pieces of coastal glaciers 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 ice shelves. by warming seas from below. Thinning and calving combined have reduced the weight of 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 by calving alone over the past quarter-century covers nearly 37,000 km2 (14,300 square miles), an area nearly the size of Switzerland, said JPL scientist Chad Greene, lead author of the study. “Antarctica is crumbling at the edges,” Greene said in NASA’s announcement of the findings. “And as 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. According to him, Antarctica has 88% of the sea level potential of all the world’s ice.
Ice shelves, permanent floating layers of frozen freshwater attached to land, take thousands of years to form and act as fulcrums holding back glaciers that would otherwise easily slide into the ocean and cause seas to rise. When ice shelves are stable, the long-term natural cycle of calving and regrowth keeps their size relatively constant. But in recent decades, warming oceans have weakened the shelves from below, a phenomenon previously documented by satellite altimeters measuring the changing height of the ice, and show losses averaging 149 million tons a year from 2002 to 2020, according to NASA.
For their analysis, Greene’s team synthesized satellite images from visible, thermal, infrared and radar wavelengths to map glacial flow and calving since 1997 more precisely than ever before along more than 50,000 km of the Antarctic coastline. Losses, as measured by calving, have so far outstripped the replenishment of the natural ice shelf that researchers have determined that Antarctica is unlikely to return to pre-glacial 2000 levels by the end of this century. Accelerated calving of glaciers, similar to thinning ice, has been most pronounced in West Antarctica, an area affected by warming ocean currents.
But even in East Antarctica, a region whose ice shelves have long been 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, a possible sign of more 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 warm periods in the past and models of what might happen in the future. The good news is that if we keep to the 2 degrees of global warming promised by the Paris Agreement, sea level rise due to the East Antarctic Ice Sheet should be moderate,” Wolff wrote in a commentary on the JPL study. however, greenhouse gas emissions would risk contributing “many meters to sea level rise over the next few centuries,” he said.
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