One of the authors said more than 110 trillion metric tonnes of ice were 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 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 resulting from burning coal, oil and natural gas. Scientists used an accepted technique for calculating minimum committed ice loss, the one used on mountain glaciers for the entire giant frozen island.

Pennsylvania State University glaciologist Richard Alley, who wasn’t part of the study but said it made sense, said the committed melting and sea level rise were like an ice cube put in a cup of hot tea in a warm room.

“You have committed mass loss from the ice,” Alley said in an email. “In the same way most of the world’s mountain glaciers and the edges of Greenland would continue losing mass if temperatures were stabilised at modern levels because they have been put into warmer air just as your ice cube was put in warmer tea.”

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Although 27cm don’t sound like much, that’s a global average. Some coastal areas would 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.

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 of Buffalo. The researchers in the study said they couldn’t estimate the timing of the committed melting, yet in the last sentence they mention, “within this century” without supporting it, Stearns said.

Colgan responded that the team didn’t know how long it would 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 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.