Earth's Ice Sheets Lost 12.5 Trillion Tons Since 1979

A major Scientific Data study finds Greenland and Antarctica lost 12.5 trillion tons of ice since 1979, driven mostly by warming ocean water.

The melt turned into nearly 3 quadrillion gallons of water and pushed global sea levels up about an inch (3.1 centimeters) on top of other climate factors. The study, led by Northumbria University ice scientist Inès Otosaka and co-authored by UC Irvine's Eric Rignot, was published Wednesday in the journal Scientific Data.

The surprising core of the study is that five-sixths of the melt — about 84% — did not come from hotter air melting ice at the surface. Instead, warmer ocean water is eating away at the ice sheets from below and the sides as glaciers flow faster into the sea. La Crosse Tribune reports that Otosaka said 84% of the ice lost came from glaciers flowing more quickly into the ocean, showing the long-term trend is driven by the ice sheets' response to a warming ocean. The Jakobshavn glacier in Greenland is now retreating up to 164 feet a day, Otosaka said.

The international team, part of the Ice Sheet Mass Balance Inter-comparison Exercise, used 27 different satellite missions and 45 independent surveys — the longest satellite record of ice sheet change ever gathered. By incorporating NASA data alongside European satellites, the scientists extended the record back to 1979 for Antarctica and 1972 for Greenland, well before earlier studies that only reached the 1990s. La Crosse Tribune reports the pace of ice loss increased by a factor of four between the 1980s and 2010s, with about 60% of the loss from Greenland and 40% from Antarctica — even though Greenland is roughly one-eighth Antarctica's size. NYU ice scientist David Holland, who was not part of the study, said the use of relatively independent methods gives him greater confidence: "The upward trend is real."

An inch of sea level rise may sound small, but Otosaka said every additional centimeter of rise puts another 2 to 3 million people at risk of flooding at least once a year. La Crosse Tribune reports the ice sheets now account for about 25% of all sea level rise, and the total rise attributed to the two ice sheets puts another 6 to 9 million people at risk of coastal flooding and erosion globally. Otosaka said the findings have implications for coastal planning, arguing the world urgently needs plans to protect coastal communities from ice sheet melting. Rignot was blunter: "We are melting the polar regions; sea level is rising worldwide and will exacerbate the vulnerability of coastal regions."

Otosaka said she has examined measurements since the study's 2023 cutoff and found the accelerating trend has picked back up. Co-author Andrew Shepherd of Northumbria said the changes are tracking decades behind global warming, meaning ice loss can be expected to continue for decades more even if the planet stops heating. Because most of the loss is dynamic, abrupt processes prone to tipping points, Holland warned it is exactly what an ice sheet instability collapse scenario would look like. University of Colorado's Ted Scambos, uninvolved in the study, called Antarctic mass loss "a clear and present danger, but many decades in the future."