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Thwaites Glacier. Credit: NASA/James Youngle
New findings from the University of Michigan reveal that the world’s largest ice sheet may be less at risk of sudden collapse than previously expected.
The study, published in the journal Science, involved simulating the demise of the Thwaites Glacier in West Antarctica, one of the largest and most stable glaciers in the world. The researchers modeled the collapse of different heights of ice cliffs – near-vertical formations that occur when glaciers and ice shelves meet the ocean. They find that instability does not always lead to rapid disintegration.
“What we found is that over long periods of time, the ice behaves like a viscous liquid, sort of like a pancake spread in a frying pan,” said Jeremy Pacis, associate professor of climate and space sciences and engineering at MM University. “So the ice is spreading and reducing faster than it can fail and that can stabilize the avalanche. But if the thin ice can’t fast enough, that is when you have the potential for rapid glacier collapse.”
The researchers combined ice collapse and ice flow variables for the first time, and found that ice expansion and loosening, as well as support from trapped ice chunks, may mitigate the effects of fracture-induced sea ice shelf instability.
The new findings add a nuance to an earlier theory called sea ice shelf instability, which suggested that if an ice shelf’s height reached a certain threshold, it could suddenly disintegrate under its own weight in a chain reaction of ice fractures. The Thwaites Glacier in Antarctica—sometimes referred to as the “Doomsday Glacier”—is approaching this threshold and could contribute about 3 feet to sea level rise in the event of a complete collapse. At 74,000 square miles, roughly the size of Florida, it is particularly vulnerable to climate and ocean changes.
The research team also found that icebergs that crack and fall away from the main glacier in a process known as “iceberg birth” may actually prevent rather than contribute to a catastrophic meltdown. If lumps of ice get stuck to outcrops on the ocean floor, they can exert reverse pressure on the glacier to help stabilize it.
Pacis notes that even if the glacier does not collapse catastrophically, exposing a towering cliff could lead to a retreat of a few kilometers per year — equal to the length of about 20 football fields — making a significant contribution to future sea-level rise.
How fast is sea level rising?
Credit: University of Michigan
While Thwaites and other glaciers are clearly melting, the speed of their demise is of great interest to coastal regions as they develop strategies for adaptation and building resilience. But forecasting glacier retreat is a very complex business, as they are influenced by the interaction of myriad factors – the stress and strain of billions of tons of moving ice, changing air and water temperatures and the effects of liquid water flow. On the ice, to name a few.
As a result, predictions of Thwaites glacier collapse range from a few decades to several centuries. Pacis says the new study is an important step toward producing accurate and actionable predictions.
“There is no doubt that the sea level is rising and that it will continue in the coming decades,” Basis said. “But I think this study offers hope that we’re not close to a complete meltdown – and that there are measures that can mitigate and stabilize things. And we still have a chance to change things by making decisions about things like energy emissions – methane and carbon dioxide.”
The fate of the Antarctic and Greenland ice sheets
In addition to Pacis, the graduate student research assistant research team includes Brandon Berg, Anna Crawford and Doug Penn from the University of St Andrews.
Crawford says the study results will also be useful in predicting the fate of glaciers and other ice formations in the Arctic and Antarctica.
“These important insights will guide future research into the retreat of the Thwaites Glacier and other large glaciers in the West Antarctic Ice Sheet that are vulnerable to retreat by ice shelf collapse and sea ice slope instability,” she said. “It highlights conditions that facilitate retreat, shows the potential for station re-stabilization and shows how sea ice can actually halt the collapse process.”
The research team is already working to improve their models further by incorporating additional variables that influence glacier retreat, including how individual glacier shapes affect their stability and the interaction between glacial ice and the surrounding liquid ocean, says Pacis.
“The ocean is always there, kind of tickling the ice in a very complex way, and we’ve only known for a decade or two how important it is,” he said. “But we’re starting to understand that it’s driving a lot of the changes we’re seeing, and I think that’s going to be the next big frontier in our research.”
The rocky path to accurate sea level predictions More information: JN Bassis et al, Transition to sea ice shelf instability controlled by ice thickness and velocity gradients, Science (2021). DOI: 10.1126 / science.abf6271 Submitted by University of Michigan
Quote: ‘Doomsday Glacier’ May Be More Stable Than Initially Expected (2021, June 18) Retrieved June 18, 2021 from https://phys.org/news/2021-06-doomsday-glacier-stable. html
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