Melting glacier sea level rise 'could be 200% worse than expected'
Scientists could have been underestimating the melting of the Greenland ice sheet by 200% meaning that sea levels could rise quicker than previously anticipated, according to a study.
New research on how the ‘grounding line’ – where an ice sheet transitions from being grounded to floating – works hints that glaciers could melt far faster than expected.
Researchers working on the Petermann Glacier in northwest Greenland found that the grounding line moves and enables warm water to reach under the glacier.
The new study shows that warm ocean water intrudes beneath the ice through preexisting subglacial channels, with the highest melt rates occurring at the grounding zone.
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Researchers at the University of California, Irvine (UCI) and NASA's Jet Propulsion Laboratory said their findings could mean that the climate community has been vastly underestimating the magnitude of future sea level rise caused by polar ice deterioration.
Using satellite radar data from three European missions, the UCI/NASA team learned that Petermann Glacier's grounding line shifts substantially during tidal cycles, allowing warm seawater to intrude and melt ice at an accelerated rate.
The results are published in the Proceedings of the National Academy of Sciences.
Lead author Enrico Ciraci, UCI assistant specialist in Earth system science and NASA postdoctoral fellow said, "Petermann's grounding line could be more accurately described as a grounding zone, because it migrates between 2 and 6 kilometers (1.2 miles to 3.7 miles) as tides come in and out.
This is an order of magnitude larger than expected for grounding lines on a rigid bed."
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The researchers found that as Petermann Glacier's grounding line retreated nearly 2.5 miles between 2016 and 2022.
Warm water carved a 670 ft cavity in the underside of the glacier, and that abscess remained there for all of 2022.
"These ice-ocean interactions make the glaciers more sensitive to ocean warming," said senior co-author Eric Rignot, UCI professor of Earth system science and NASA JPL research scientist.
"These dynamics are not included in models, and if we were to include them, it would increase projections of sea level rise by up to 200% – not just for Petermann but for all glaciers ending in the ocean, which is most of northern Greenland and all of Antarctica."
The Greenland ice sheet has lost billions of tons of ice to the ocean in the past few decades, the PNAS paper stresses, with most of the loss caused by warming of subsurface ocean waters, a product of Earth's changing climate.
Exposure to ocean water melts the ice vigorously at the glacier front and erodes resistance to the movement of glaciers over the ground, causing the ice to slide more quickly to the sea.
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