Greenland’s rapidly melting ice sheet will eventually raise global sea levels by at least 27 centimeters — more than twice as much as previously predicted — according to a study published Monday.
That’s because of something that could be called zombie ice cream. That’s doomed ice that, while still clinging to thicker areas of ice, is no longer replenished by parent glaciers that now receive less snow. Without replenishment, climate change will melt the doomed ice and inevitably raise the seas, said study co-author William Colgan, a glaciologist with the Geological Survey of Denmark and Greenland.
‘It’s dead ice. It’s just going to melt and disappear from the ice sheet,” Colgan said in an interview. “This ice has been sent to the ocean no matter what climate (emissions) scenario we take now.”
Study lead author Jason Box, a glaciologist with the Greenland survey, said it’s “more like a foot in the grave.”
The unavoidable ten centimeters in the study is more than twice the sea level rise scientists previously expected from the melting of the Greenland ice sheet. The study in the journal Nature Climate Change said it could grow as high as 30 inches (78 centimeters). By contrast, last year’s report from the Intergovernmental Panel on Climate Change predicted a range of 2 to 5 inches (6 to 13 centimeters) for likely sea level rise from the melting of the Greenland ice by the year 2100.
What scientists did for the study was look at the ice in balance. In perfect balance, snowfall in the mountains of Greenland flows down and charges and thickens the sides of glaciers, balancing melting at the edges. But in recent decades, there has been less replenishment and more melting, creating imbalances. Study authors looked at the ratio of what is added to what is lost and calculated that 3.3% of Greenland’s total ice volume will melt, no matter what happens if the world reduces carbon pollution, Colgan said.
“I think starving would be a good term,” for what’s happening to the ice, Colgan said.
One of the study’s authors said more than 120 trillion tons (110 trillion metric tons) of ice are already doomed to melt due to the warming ice sheet’s inability to replenish its edges. When that ice melts into water, if it were concentrated only over the United States, it would be 37 feet (11 meters) deep.
The numbers are a global average for sea level rise, but some places further from Greenland would get more and places closer, like the US East Coast, would get less. While 10.6 inches may not sound like much, this would be more than high tides and storms, making them worse, so that much sea level rise “will have huge social, economic and environmental consequences,” said Ellyn Enderlin, a professor of geosciences. at Boise State University, which was not part of the study.
“This is a really big loss and will adversely affect coastlines around the world,” said NYU’s David Holland, who has just returned from Greenland but is not part of the study.
This is the first time scientists have calculated minimal ice loss — and associated sea level rise — for Greenland, one of Earth’s two massive ice sheets that are slowly shrinking. as a result of climate change from the burning of coal, oil and natural gas. Scientists used an accepted technique for calculating the minimum recorded ice loss, the technique used on mountain glaciers for the entire giant frozen island.
Richard Alley, a Pennsylvania State University glaciologist, who was not part of the study but said it made sense, said the committed melting and sea-level rise is like an ice cube put in a cup of hot tea in a warm room.
“You have committed massive loss of the ice,” Alley said in an email. “In the same way, most mountain glaciers and the rims of Greenland would continue to lose mass if temperatures stabilized at modern levels, because they were put in warmer air, just like your ice cube was put in warmer tea.”
Time is the key unknown here and a bit of a problem with the study, said two outside ice scientists, Leigh Stearns of the University of Kansas and Sophie Nowicki of the University at Buffalo. The researchers in the study said they couldn’t estimate the timing of the committed melting, but in the last sentence they call it “within this century,” without backing it up, Stearns said.
Colgan replied that the team doesn’t know how long it will take for all the doomed ice to melt, but with an informed guess, it would probably be by the end of this century, or at least by 2150.
Colgan said this is actually all a best case scenario. The year 2012 (and to a different extent 2019 ) was a huge melting year, when the balance between adding and subtracting ice was most out of balance. If Earth begins to undergo more years like 2012, Greenland’s melting could lead to 30 inches (78 centimeters) of sea level rise, he said. Those two years now seem extreme, but years that look normal now would have been extreme 50 years ago, he said.
“That’s how climate change works,” Colgan said. “Today’s outliers become tomorrow’s averages.”
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