Zombie ice from the massive Greenland Ice Sheet will eventually raise global sea levels by at least 10 inches (27 centimeters) on its own, according to a study published Monday.
Zombie or doomed ice is ice that is still attached to thicker areas of ice, but is no longer fed by these larger glaciers. This is because the parent glaciers are receiving less snow. Meanwhile, the doomed ice is melting because of climate change, 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. “That ice has been sent into the ocean, regardless of the climate (emissions) scenario we do now.”
Lead study author Jason Box, a Greenland survey glaciologist, said it’s “more like a foot in the grave”.
The study’s inevitable ten inches is more than double the sea level rise scientists had previously expected from the melting of the Greenland ice sheet. The study in the journal Nature Climate Change said it could reach up to 30 inches (78 centimeters). By contrast, last year’s Intergovernmental Panel on Climate Change report projected a range of 2 to 5 inches (6 to 13 centimeters) for likely sea level rise from melting ice of Greenland in 2100.
What the scientists did for the study was look at ice at equilibrium. In perfect balance, snowfall in the mountains of Greenland flows down and recharges and thickens the sides of the glaciers, balancing what melts at the edges. But in recent decades there has been less replenishment and more fusion, creating an imbalance. The study authors analyzed the ratio of what is added to what is lost and calculated that 3.3% of the total volume of Greenland ice will melt, regardless of what happens with the reduction of carbon pollution in the world, Colgan said.
“I think starving would be a good phrase,” Colgan said.
One of the study’s authors said that more than 120 trillion tons (110 trillion metric tons) of ice is already doomed to melt due to the inability of the warming ice sheet to replenish its edges. When that ice melts into water, if concentrated in the United States alone, it would be 11 meters deep.
This is the first time scientists have calculated a minimum ice loss, and accompanying sea level rise, for Greenland, one of Earth’s two massive ice sheets that are slowly shrinking to cause of climate change from the burning of coal, oil and natural gas. The scientists used an accepted technique to calculate the minimum committed ice loss, the one used on mountain glaciers for the entire giant ice island.
Glaciologist Richard Alley of Pennsylvania State University, who was not part of the study but said it made sense, said the compromised melting and sea level rise is like an ice cube put in a cup of hot tea in a warm room.
“You have committed a massive loss of ice,” Alley said in an email. “Similarly, most of the world’s mountain glaciers and the edges of Greenland would continue to lose mass if temperatures stabilized at modern levels because they have been put into warmer air in the same way that your cube of ice was put into a hotter tea.”
While 10 inches doesn’t sound like much, that’s an overall average. Some coastal areas will be hit harder, and high tides and storm surges could be even worse, so this sea level rise “will have huge social, economic and environmental impacts,” said Ellyn Enderlin, professor of geosciences. in Boise. State University
Time is the key unknown here and somewhat 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 study’s researchers said they could not estimate the timing of the proposed merger, but in the last sentence they mention “within this century,” without supporting it, Stearns said.
Colgan replied that the team doesn’t know how long it will take for all of the damned ice to melt, but making an educated guess, it would probably be by the end of this century or at least 2150.
Colgan said all of this is actually a best-case scenario. 2012 (and to varying degrees 2019) was a year of enormous melting, when the balance between adding and subtracting ice was most unbalanced. If Earth begins to experience more years like 2012, the melting of Greenland ice could lead to 30 inches (78 centimeters) of sea level rise, he said. Those two years seem extreme now, but the years that seem 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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