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 released Monday.
Zombie ice 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 receive less replenishing snow. Meanwhile, the doomed ice sheets are melting from climate change, said study co-author William Colgan, a glaciologist at the Geological Survey of Denmark and Greenland.
“It’s dead ice. It will just melt and disappear from the ice sheet,” Colgan said in an interview. “That ice has been sent to the ocean regardless of the climate (emissions) scenario we’re going with now.”
The study’s lead author Jason Box, a glaciologist at the Greenland Survey, said “it’s more like one foot in the grave.”
The inevitable ten inches in the study is more than twice as much sea level rise as scientists 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 cm). In contrast, last year’s report by the Intergovernmental Panel on Climate Change predicted a range of 2 to 5 inches (6 to 13 centimeters) of possible sea-level rise from melting Greenland ice by the year 2100.
What the scientists did for the study was look at the ice in equilibrium. In perfect balance, snowfall in the Greenland mountains 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 melting, creating an imbalance. The study authors looked at the ratio of what is being added to what is being lost and estimated that 3.3 percent of Greenland’s total ice volume will melt no matter what happens with the reduction in carbon pollution, Colgan said.
“I think hunger would be a good phrase,” for what’s happening on the ice, Colgan said.
One of the study’s authors said more than 120 trillion tons (110 trillion metric tons) of ice is already doomed to melt because of the warming ice sheet’s inability to replenish its edges. When this ice melts into water, if it were concentrated in the United States alone, it would be 37 feet (11 meters) deep.
This is the first time scientists have estimated a minimal loss of ice — and accompanying sea level rise — for Greenland, one of Earth’s two vast ice sheets slowly shrinking due to climate change from burning coal , oil and natural gas. The scientists used an accepted technique to calculate the minimum ice loss, the one used in mountain glaciers for the entire giant frozen island.
Glaciologist Richard Alley of Pennsylvania State University, who was not involved in the study but said it made sense, said melting and rising sea levels are like an ice cube placed in a cup of hot tea in a warm room.
“You have committed ice mass loss,” Alley said in an email. “In the same way 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, like your ice cube went into warmer tea.” .
While 10 inches doesn’t sound like much, that’s a global average. Some coastal areas will be hit harder, and high tides and storm surges could be even worse, so this big sea-level rise “will have huge social, economic and environmental impacts,” said Ellyn Enderlin, professor of geosciences at Boise. State University.
Timing is the key unknown here and a small 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 frozen melt, but in the last sentence they say, “within this century,” without backing it up, 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 by 2150.
Colgan said that’s actually the best case scenario. The year 2012 (and to a different extent 2019 ) was a massive melt year, when the balance between adding and removing ice was very out of balance. If Earth starts to experience more years like 2012, melting Greenland could cause sea levels to rise by 30 inches (78 centimeters), he said. Those two years seem extreme now, but years that seem normal now would have been extreme 50 years ago, he said.
“That’s how climate change works,” Colgan said. “Today’s extremes become tomorrow’s averages.”
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