Greenland and Antarctica lost 12 trillion tons of ice in 47 years

NYU student researchers sit on top of a rock overlooking the Helheim glacier in Greenland (2019) [AP Photo]

About 12.5 trillion tons (11.3 trillion metric tons) of ice from glaciers in Greenland and Antarctica have melted since 1979, which is enough frozen water to stack ice five feet deep across the continental United States, 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 University of California, Irvine. “We are melting the polar regions, sea level is rising worldwide and will exacerbate the vulnerability of coastal regions.”

Huge numbers for ice melt, people flooded

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

All that melted ice turned into nearly 3 quadrillion gallons of water (11.3 quadrillion liters), which pushed global sea levels up about an inch (3.1 centimeters) since 1979, on top of other climate factors raising ocean heights, the report said.

An inch may not sound like much, but for every third of an inch (or centimeter) of sea level rise, another 2 to 3 million people get 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 now retreating up to 164 feet (50 meters) 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.

The melting is accelerating

“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. “And that’s quite clear that there’s a link to climate change.”

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

“That’s something to be concerned about as it shows that 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 back up.

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.”

Worrying about a collapse scenario

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’s 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 now as a society smart enough to know the future, but not prudent enough to act upon the knowledge.” SETH BORENSTEIN, AP Science Writer, MDT/AP