Researchers studying the Petermann Glacier, one of Greenland’s biggest, have discovered a troubling melting trend that, if occurring elsewhere, could mean current estimates of sea-level rise due to shrinking glaciers should be doubled, reports the team in a new study, published this month in Proceedings of the National Academy of Sciences.
As increasingly warmer seawater moves in and out with the tides, it has carved a 670-foot cavity underneath Petermann’s ice—roughly the size of two Statues of Liberty stacked on top of each other. At the grounding line—the spot where the part of the glacier on land meets the part that floats—water is seeping beneath the ice for more than a mile inland, multiple times a day, speeding up melt.
“The sea water actually goes much farther beneath the grounded ice [than previously thought]—kilometres, not hundreds of meters,” senior author Eric Rignot, an Earth system scientist at the University of California, Irvine, and a NASA research scientist, tells the Associated Press’ Seth Borenstein. “And that water is full of heat and able to melt the glaciers vigorously. And it’s kind of the most sensitive part of the glacier.”
In the study, glaciologists used satellite data to track the Petermann Glacier’s measurements and changes over several years. By documenting the ice’s height and how the glacier responds to tides, the team predicted what was happening at the difficult-to-observe grounding line. They discovered the massive cavity beneath the glacier, where melting has accelerated—in the last three years, the rate of melt was 50 percent higher than it was from 2016 to 2019.
If that rapid pace of melting is happening elsewhere in Greenland and along the Antarctic ice sheet, that means global predictions for sea-level rise so far have captured just the tip of the iceberg.
“These ice-ocean interactions make the glaciers more sensitive to ocean warming,” says Rignot in a statement. “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 percent—not just for Petermann but for all glaciers ending in the ocean, which is most of northern Greenland and all of Antarctica.”
As human-caused climate change heats the planet and melts ice, a vicious cycle emerges: Warming waters eat away at glaciers, which contributes to sea levels rising higher; this brings glaciers into more contact with the ocean, which leads to even more melting. Already, “the Greenland ice sheet has lost billions of tons of ice to the oceans in the last few decades,” which has increased sea levels by 0.5 inches since the early 1970s, the researchers write.
Andreas Muenchow, an oceanographer at the University of Delaware who studies Petermann Glacier but was not involved in the new paper, tells the Washington Post’s Chris Mooney that it will take much more time and research to widely apply the model used in this study. “The very high melt rates are real, but they are estimated over very small areas.”
“My main takeaway is that models need to be improved,” Muenchow says to the Post. “The study provides a sharper focus for what processes we need to study near floating glaciers in Greenland or Antarctica, if we want to project rising sea level into the future using models.”
Sea-level rise is already impacting coastal communities all over the world—and data show it is accelerating. Waters along United States coastlines are on track to rise up to one foot by 2050, according to a study last year. Greenland’s melting ice is the largest single source contributing to sea-level rise, per NASA.