Extreme melt reduced Greenland ice sheet storage, according to a study

The vast melting of Greenland's ice sheet caused by unusually high temperatures in 2012 had a lasting impact on its ability to absorb and store future meltwater, new research showed Tuesday.

Authors of the research said it was evidence of how one-off or rare weather events could have a lasting impact on Earth's frozen spaces and a knock-on effect on global sea levels.

In summer 2012, much of the Arctic sweltered in a rare heatwave that saw blue lakes glimmering across Greenland's previously frozen ice sheet.

Using advanced modelling techniques, a team of researchers in the US reanalysed radar data collected by flights from NASA's Operation IceBridge between 2012-2017 to interpret melting near the surface of the ice sheet.

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Ice sheet regions that haven't undergone extreme melting can store meltwater throughout their upper 50 metres or so, preventing it from flowing into the ocean.

But the team found that the melting in 2012 had refrozen into a layer of slick ice, creating slippery conditions that can speed up its movement and send chunks into the ocean.

In some parts of the Greenland Ice Sheet, the team found that the melt layer had reduced its storage capacity to just five metres.

"When you have these extreme, one-off melt years, it's not just adding more to Greenland's contribution to sea-level rise in that year," said lead study author Riley Culberg, from Stanford University.

"It's also creating these persistent structural changes in the ice sheet itself."

The Greenland Ice Sheet has experienced five record-breaking melt seasons since 2000, most recently in 2019.

Satellite data from 2021 showed that in the course of just a few July days, as much as 97 percent of the ice sheet surface had thawed.

And with the poles warming significantly faster than the rest of the planet, more extreme and regular hot weather over the Arctic is set to increase Greenland melt events.

"Normally we'd say the ice sheet would just shrug off weather -- ice sheets tend to be big, calm, slow things," said Dustin Schroeder, assistant professor of geophysics at Stanford's School of Earth, Energy and Environmental Sciences.

"This really is one of the first cases where you can say, shockingly in some ways, these slow, calm ice sheets care a lot about a single extreme event in a particularly warm year."

The Greenland Ice Sheet contains enough frozen water to raise global sea levels around six metres, and along with the vast ice shelves of Antarctica is among the most complex elements to factor into climate models.

Authors of the study, published in the journal Nature Communications, could contain lessons applicable to Antarctica as the continent experiences hotter temperatures.

"The melt event in 2012 is impacting the way the ice sheet responds to surface melt even now," said Culberg.

"These structural changes mean the way the ice sheet responds to surface melting is going to be impacted longer term."