Starved Greenland ice to raise global sea levels by 'unavoidable' 27cm

Zombie ice from the massive Greenland ice sheet will eventually raise global sea level by at least 27 centimetres or 10 inches on its own but with an uneven impact that could be devastating for certain coastal areas.

Zombie or doomed ice is ice that is still attached to thicker areas of ice, but is no longer getting fed by those larger glaciers. That's because the parent glaciers are getting less replenishing snow. 

The doomed ice is melting from climate change, said the co-author of a study released on Monday William Colgan.

“It’s dead ice. It’s just going to melt and disappear from the ice sheet,” Colgan, who is a glaciologist at the Geological Survey of Denmark and Greenland, said in an interview. 

“This ice has been consigned to the ocean, regardless of what climate (emissions) scenario we take now.”

Study lead author Jason Box, a glaciologist at the Greenland survey, said it is “more like one foot in the grave.”

The unavoidable 27 centimetres in the study is more than twice as much sea level rise as scientists had previously expected from the melting of Greenland’s ice sheet. The study in the journal Nature Climate Change said it could reach as much as 78 centimetres (30 inches). 

By contrast, last year’s Intergovernmental Panel on Climate Change report projected a range of 6 to 13 centimetres (2 to 5 inches) for likely sea level rise from Greenland ice melt by the year 2100.

READ MORE: Billionaires turn to reap benefits from melting glaciers

Starving ice

What scientists did for the study was look at the ice in balance. 

In perfect equilibrium, snowfall in the mountains in Greenland flows down and recharges and thickens the sides of glaciers, balancing out what’s melting on the edges. But in the last few decades there’s less replenishment and more melting, creating imbalance. 

Study authors looked at the ratio of what’s being added to what’s being lost and calculated that 3.3 percent of Greenland’s total ice volume will melt no matter what happens with the world cutting carbon pollution, Colgan said.

“I think starving would be a good phrase,” for what’s happening to the ice, Colgan said.

One of the study authors said that more than 110 trillion metric tonnes of ice is already doomed to melt from 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 11 metres (37 feet) deep.

This is the first time scientists calculated a minimum ice loss  — and accompanying sea level rise — for Greenland, one of Earth’s two massive ice sheets that are slowly shrinking because of climate change from burning coal, oil and natural gas. 

Although 27 centimetres doesn't sound like much, that's a global average. 

Some coastal areas will be hit with more, and high tides and storms on top of that could be even worse, so this much sea level rise “will have huge societal, economic and environmental impacts,” said Ellyn Enderlin, a geosciences professor at Boise State University.

Timing of committed melting

Colgan responded that the team doesn’t know how long it will take for all the doomed 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 this is actually all a best case scenario. 

The year 2012 (and to a different degree 2019 ) was a huge melt year, when the equilibrium between adding and subtracting ice was most out of balance. If Earth starts to undergo more years like 2012, Greenland melt could trigger 78 centimetres (30 inches) of sea level rise, he said. Those two years seem extreme now, 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.”

READ MORE: Greenland ice sheet shrinks by record amount - climate study