Satellites show Earth lost nearly 12-trillion tonnes of ice from Greenland, Antarctica in 47 years

About 11.3-trillion tonnes of ice from glaciers in Greenland and Antarctica have melted since 1979, which is enough frozen water to stack ice 1.5m deep across the continental US, according to a major scientific report.

A warming Earth is accelerating the melting of the planet’s two major ice sheets, with five-sixths of the melt not coming from hotter air, but from warmer waters eating away at the ice sheets from below and the sides, with glaciers flowing into the oceans, according to a study in Wednesday’s journal Scientific Data. That’s bad news for future sea level rise, the study’s authors said.

“The ice sheets are melting away fast,” said study co-author Eric Rignot, an ice scientist at the University of California, Irvine. “We are melting the polar regions, sea level is rising worldwide and will exacerbate the vulnerability of coastal regions.”

The numbers behind the melt are mind-bogglingly huge and deceptively small.

All the melted ice turned into nearly 11.3-quadrillion litres of water, which pushed global sea levels up by about 3.1cm since 1979, on top of other climate factors raising ocean heights, the report said.

A few centimetres may not sound like much, but for every centimetre of sea level rise, another 2- to 3-million people are flooded at least once a year, said lead study author Ines Otosaka, an ice scientist at Northumbria University in England.

The Jakobshavn glacier in Greenland is retreating by up to 50m a day, Otosaka said.

The international collaboration of polar scientists, headed by the European Space Agency, had in the past only looked at ice sheet melt since the 1990s based on European satellite data. But by incorporating Nasa satellites, the scientists were able to chart ice sheet volumes in Antarctica back to 1979 and in Greenland back to 1972.

“There is a clear trend that the ice sheets are losing more mass and it has been increasing from decade to decade, especially if you look at the ice being discharged to the ocean,” Otosaka said. “That’s quite clear that there’s a link to climate change.”

It showed in the 1970s, 1980s and into the 1990s, the ice sheets were relatively stable, but then melting started happening and really kicked in during the 2010s, Otosaka said.

“That’s something to be concerned about as it shows the changes are tracking decades behind global warming, which means we can expect them to continue for decades more, even if we are able to stop heating the planet,” said study co-author Andrew Shepherd, also of Northumbria.

The accelerating numbers seemed to pause from 2020 to 2023, but the study’s authors said it more reflected short-term weather variations not long-term trends. Otosaka said the study stopped with 2023 data, but she’s looked at measurements since and found the accelerating trend has picked up again.

A lot of the stability in Antarctica was because east Antarctica had record snowfall, which compensated for the rapid melting in the less stable west Antarctic ice sheet, the authors said.

The three-year hiatus was “just a bump in the record”, Rignot said. “The long rise is climate and the threat is crystal clear.”

The biggest changes scientists saw are in what they call dynamic processes, which are more abrupt and active than the slow steady melting from the air, and that’s something prone to trigger runaway “tipping points”, Otosaka said.

New York University ice scientist David Holland said that is what concerns him “because most of the ice loss is dynamical and that is exactly what you would expect in an ice sheet instability collapse scenario”.

The international team used 45 independent surveys and 27 different satellites. “The use of relatively independent methods gives me greater confidence in the result,” said Holland, who wasn’t part of the study. “The upward trend is real.”

“The ‘wild cards’ of Antarctic mass loss continue to pose a challenge for human management of the planet, a clear and present danger, but many decades in the future,” said University of Colorado ice scientist Ted Scambos, who wasn’t part of the study. “We are as a society smart enough to know the future, but not prudent enough to act on the knowledge.”