LONDON – The Greenland ice sheet, an expanse of frozen water about three times the size of Texas, is disappearing much faster than previously thought, according to new research, and the difference may already be affecting the distribution of heat around the world.

The mass of ice lost between 1985 and 2022 has been underestimated by as much as 20 per cent, or more than one trillion metric tonnes of ice. This is due to the overlooked impact of calving around Greenland’s perimeter, where the sheet’s glaciers meet the sea, scientists wrote in an article published on Jan 17 in Nature.

Using several public datasets, the research team combined more than 235,000 observations of glacial end points to create an “ice mask” showing the extent of the ice sheet every month from 1985 to 2022.

“The surprise was just the ubiquity of the signal,” said Dr Chad Greene, a glaciologist with Nasa’s Jet Propulsion Laboratory in Pasadena, California, and lead author of the study.

With the exception of “one minuscule little glacier” that grew modestly, Dr Greene said, “there has just been retreat everywhere we’ve looked. It’s on every corner of the island”.

The shrinking of Greenland’s ice sheet is already contributing to higher seas, but the melting studied by Dr Greene and his team likely had minimal impact because it occurred in deep fjords leading into the ocean, where the ice was already mostly underwater. However, as that part of the glaciers disappears, inland melting is likely to accelerate and will raise sea levels as that water flows into the ocean.

“What we’re seeing is that the clog in this bottleneck has been removed and, as a result, the glaciers all around Greenland have been able to speed up (the melting process),” he said. “You take the ice out of the fjord and glaciers speed up and start contributing to sea-level rise.”

Figuring out how much more ice is going to be lost, and how quickly, also depends on the sensitivity of various glaciers to climate change. The extent of the glaciers fluctuates seasonally, growing in winter and retreating in summer. Those that consistently changed the most are likely the most sensitive to environmental change and global warming, the scientists surmised.

“This finding is sort of laying a road map of where to look for which glaciers that are going to be potentially the biggest players over the next few decades in sea-level rise,” Dr Greene said.

Greenland’s ice sheet is retreating because of warmer global temperatures caused by the human combustion of fossil fuels. Prior to this study, the total mass loss from the sheet so far was estimated at about five trillion metric tonnes, according to Imbie, a collaboration of polar scientists. Were it all to melt, sea levels could rise more than 7m.

Meanwhile, the loss through calving – when icebergs break off the glacier and float out to sea – is already significant enough that it may be affecting ocean circulation and the distribution of heat energy around the globe, the study suggests. This could have particular importance for Atlantic Meridional Overturning Circulation, or Amoc.

Amoc can be described as a planetary conveyor belt of energy that circulates warm water from lower latitudes up to the North Atlantic and back again. In addition to warming much of Europe and Britain, that circulation carries nutrients with it that are key to sustaining ocean life.

The annual freeze of the surface of the Arctic Ocean is a driver of the conveyor belt. Ice cannot contain salt, and so as Arctic sea ice freezes, the salt is pushed out and sinks to the bottom of the sea. This denser salt water then flows south, which, in turn, pulls warm water north.

Scientists are divided as to whether Amoc is approaching a tipping point when even a relatively small amount of melting fresh water could disrupt the cycle. But it seems likely that a larger inflow could have an impact. 

“We found an extra thousand gigatons (of lost ice) and now, we’re saying to ocean modellers, ‘Put this in your models and see if it affects things’,” Dr Greene said.

That 1,000 gigatons (1 trillion tonnes) figure is significant and “much larger than I would have hypothesised”, said Dr Julienne Stroeve, chief science officer at Arctic Basecamp, a non-profit group of Arctic experts, and a professor of polar observation and modelling at University College London.

The impact that it may be having on ocean circulation warrants investigation, Dr Stroeve said.

“The only region of the planet that’s kind of cooling is actually off the south-eastern coast of Greenland, in the ocean, and that could be due to freshening of the ocean from more meltwater from Greenland.” 

Whether it is also contributing to larger changes in ocean circulation partly depends on where the fresh water ultimately ends up, as the icebergs float away from Greenland and melt and, more importantly, on the quantity of fresh water entering the ocean, she said.

Until now, scientists have believed that most ice loss in Greenland is caused by increased surface melting and run-off, not calving. 

“I do wonder now what the mass balance between calving and surface melt is, because many scientists have been saying that surface melt was more important,” said Dr Stroeve. “But this might change that story.” BLOOMBERG