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West Antarctic Ice Sheet collapse may be unavoidable, study finds

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West Antarctic Ice Sheet collapse may be unavoidable, study finds

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The most comprehensive effort yet to predict how global warming will affect the West Antarctic Ice Sheet has found there is little humanity can do to stop its ice shelves from melting, which could collapse the sheet and raise sea levels by several feet in the coming centuries.

The report, published Monday in the journal Nature Climate Communications, is a full-throated warning that one of the worst sea-level rise scenarios scientists have cautioned about since the 1970s is most likely in progress and that little can be done to stop it. 

The study is the first attempt to model the uncertain atmosphere and ocean processes that could doom the ice shelves, and it doesn’t factor all of the variables that could play a role in melting. Key questions remain unanswered, including how much melt our emissions to date will cause and how fast it is expected to happen.    

“It appears we may have lost control of the west Antarctic ice shelf melting over the 21st century,” said Kaitlin Naughten, an ocean modeler with the British Antarctic Survey, who is the lead author of the new study. “West Antarctic ice shelf melting is one impact of climate change that we’re probably just going to have to adapt to, and that very likely means some amount of sea level rise we cannot avoid. Coastal communities will either have to build around or be abandoned.”

Coastal communities will either have to build around or be abandoned.

Kaitlin Naughten, an ocean modeler with the British Antarctic Survey

The West Antarctic Ice Sheet, near the southern tip of South America, is considered by scientists to be one of the most important potential contributors to sea level rise because of climate change. The marine ice sheet sits on bedrock below sea level, contains glaciers that flow toward the sea and is surrounded by floating ice shelves. 

Outside researchers said the study represented an important advance in understanding the stresses a warming ocean will put on this critical ice sheet. 

“There’s uncertainty in what the ice sheet will do, and there’s uncertainty in what climate it will feel,” said Eric Steig, the chair of the Department of Earth and Space at the University of Washington, who was not involved in the study. “It’s a really important paper because it’s the first to take a comprehensive view of the uncertainties in the climate part of the story.” 

The study doesn’t make specific sea level rise predictions, but outside researchers have estimated in the past that the total collapse of the West Antarctic ice sheet could contribute about 10 feet to overall sea level rise. 

The melt process would likely take several centuries, Steig said. Other processes are contributing to sea level rise, including the melting of Greenland’s ice sheet, the loss of mountain glaciers and the expansion of ocean water due to warming. Researchers are scrambling to understand these complicated ice sheet dynamics and whether there are critical thresholds for runaway melt.  

Without adaptation, 10 feet of sea level rise would likely submerge much of Miami and South Florida, make Baton Rouge, Louisiana, oceanfront property and inundate the Brooklyn neighborhood of Red Hook in New York City, according to National Oceanic and Atmospheric Administration maps that give rough estimates of sea level changes.

The United Nations Intergovernmental Panel on Climate Change (IPCC) in its 2021 report estimated that the sea level would rise  0.9 to 3.3 feet (0.28 to 1.01 meters), but said those numbers didn’t factor uncertain ice sheet processes like the ones being studied in this new paper. Naughten said her findings suggest those estimates are too low. 

“I would personally double any number IPCC has. They’re fairly conservative,” said David Schneider, a polar scientist and climate modeler at the University of Colorado in Boulder, who was not involved in the new study. “I’d put an upper bound of 2 meters, at least, with a lot of uncertainty.”

The new study suggests that changes to ocean circulation caused by global warming allow more warm water to eat away at the ice shelves in the Amundsen Sea, accelerating melting. The ice shelves buttress glaciers within the West Antarctic Ice Sheet. Those glaciers would likely see “irreversible retreat” — collapsing the ice sheet, the study says. 

The scientists modeled how the system would respond in several climate scenarios, including the most aggressive emission reductions world leaders are considering. Nothing made a substantive difference over the next several decades.

Even if humans stopped all fossil fuel use today and shut off the faucet of greenhouse gas emissions, “it wouldn’t be an on-off switch” for the ice shelves, said Catherine Walker, a glaciologist at the Woods Hole Oceanographic Institute, a nonprofit research organization in Massachusetts, who studies Antarctica and was not involved in the study. “The processes already in motion would carry the current setting through over several decades.”

The study is the most comprehensive modeling of future ocean conditions and how they will stress the ice sheet, but it’s a single model that should be replicated and expanded upon, experts say. The model doesn’t factor all the complexities of the melt out, including changes to snowfall or how the ice sheet’s geometry will change as it melts. 

“This is a first effort, and there’s a lot of stuff that’s unknown and that they’ve left out,” Steig, of the University of Washington, said. 

Steig said he would bet — based on his own research and from following other Antarctic scientists’ work for decades — that it will take hundreds or thousands of years for the effects of global warming to collapse the West Antarctic Ice Sheet. 

“Things are not looking great for Antarctica,” Steig said. But, this new study, which Steig said was novel, based on solid science and reputable, doesn’t give him more confidence in that bet. “It gives me the same level of uncertainty I already had.” 

The next step for this line of research is to combine these findings with a detailed ice sheet model to see how it cracks and evolves. 

“An extra piece to this puzzle is: How does the ice melt?” said Walker, of Woods Hole. “That’s a giant question and drives some of the largest uncertainties of sea level rise.”

This modeling research is also limited by a relatively short history of observational data  from satellites, field science or weather stations that could help guide the model to a more accurate result. Incorporating more information about past climates could help researchers piece together what ice previously existed. 

Peter Neff, a glaciologist, climate scientist and assistant research professor at the University of Minnesota who was not involved in the study, said its findings are “constrained” because there hasn’t been enough on-the-ice science near the Amundsen Sea Coast, which is known for its foul weather and remote location. 

Neff is traveling to an area near West Antarctica’s Thwaites Glacier — sometimes called the Doomsday Glacier — this January to collect the first modern climate-focused ice core from the Amundsen Sea coast area. Ice cores are long cylinders of ice drilled out of the surface. The internal chemistry of different layers of the ice can be analyzed to tell what climate conditions were like in the past. 

“We want things to be grounded by observations,” Neff said, to prove the model can accurately represent the past and predict the future. 

Scientists will go about gathering new data, reducing the uncertainty and providing a clear view of what’s to come with sea level rise. All of the researchers agreed: Much higher seas are coming and policymakers must prepare now. 

“If we can plan ahead to reduce human suffering and save human lives, that’s better than closing our eyes when the ocean is on our doorstep,” Naughten, the study’s lead author, said. 

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