A 47-year satellite vigil over the planet's polar regions has produced a sobering ledger: Greenland and Antarctica have together shed roughly 12.5 trillion tons (11.3 trillion metric tons) of ice since 1979. Spread across the continental United States, that much frozen water would form a sheet 5 feet (1.5 meters) deep.
The accounting comes from a major scientific report published Wednesday in the journal Scientific Data. It was produced by an international collaboration of polar researchers led by the European Space Agency, and its central message is that a warming world is speeding the loss of the planet's two largest ice sheets — with consequences that will be felt far from the poles.
A dozen trillion tons, tallied from orbit
To measure how much ice the sheets have surrendered, the team combined observations from European and NASA satellites, tracking changes in ice volume rather than leaning on any single instrument. The result is a long-term record spanning nearly half a century.
Translated into liquid, the disappearance is almost impossible to picture: nearly 3 quadrillion gallons (11.3 quadrillion liters) of water. That influx has pushed global sea levels up by about an inch (3.1 centimeters) since 1979, according to the report — a rise that stacks on top of other climate-related factors also lifting ocean heights.
Huge in tons, modest in inches
The study's numbers are, in the authors' framing, both staggering and deceptive. Trillions of tons of ice sound like an unfathomable quantity, and they are. An inch of sea level rise sounds trivial, and it is not. That mismatch is precisely the point the researchers want to convey: a small-sounding average hides an enormous volume of water and very real consequences at the shoreline.
The five-foot continental comparison is one way to make the total tangible. The sea level figure is another — and, the authors argue, the more consequential one for planning purposes.
The ocean is doing most of the melting
One of the report's most consequential findings concerns the mechanism behind the melt. Roughly five-sixths of the ice loss is not driven by hotter air, but by warmer ocean water attacking the ice sheets from below and along their sides.
That distinction matters. Where glaciers meet the sea, relatively mild water can undercut and thin the ice from beneath, while the glaciers themselves keep flowing outward into the ocean. Air temperatures still play a role, but the study identifies the sea as the dominant force stripping mass from Greenland and Antarctica.
"The ice sheets are melting away fast," said co-author Eric Rignot, an ice scientist at the University of California, Irvine. He warned that the polar regions are being melted and that sea level is rising worldwide, deepening the vulnerability of coastal regions.
Every centimeter of sea level has a price
For coastal planners, the abstract figure of an inch becomes concrete when it is converted into people. Ines Otosaka, the study's lead author and an ice scientist at Northumbria University in England, said that for every third of an inch — one centimeter — of sea level rise, another 2 to 3 million people are flooded at least once a year.
Otosaka illustrated the pace of change with a single glacier: Jakobshavn in Greenland, which is now retreating by as much as 164 feet (50 meters) a day.
Extending the record back to 1979
The length of the new record is itself a step forward. In earlier phases, the collaboration relied on European satellite data and could only examine ice sheet melt from the 1990s onward. By folding in NASA satellite observations, the scientists were able to reconstruct ice sheet volumes in Antarctica as far back as 1979 and to push the Greenland series further into the past as well.
That longer view captures decades of change that shorter records would miss, and it lets researchers separate a persistent trend from ordinary year-to-year variability.
Why the findings matter
- Acceleration: The data indicate that a warming planet is speeding the melt of both major ice sheets, not merely nudging it.
- An underestimated driver: Because most of the loss traces to warm ocean water at the ice margins, monitoring and modeling must treat ocean conditions as carefully as air temperatures.
- Compounding sea level rise: The inch of rise attributed to ice sheet melt sits atop other climate-driven contributions to ocean height, so total exposure for coastal areas is larger than this study alone implies.
- Human stakes: Each additional centimeter of sea level translates into millions more people facing at least annual flooding.
What to watch next
Rignot's warning frames the study's broader implication: the polar regions are losing mass quickly, and the resulting increase in sea level will amplify the exposure of coastal regions worldwide. The researchers' hope is that a record stretching back to 1979 — anchored in satellite measurements of ice volume rather than short-term snapshots — gives policymakers and scientists a firmer baseline for understanding where the ice sheets are heading.
For now, the ledger is unambiguous. In 47 years, more than 12 trillion tons of ice have left Greenland and Antarctica — enough to cover the continental United States in five feet of ice, and enough to lift the world's oceans about an inch.
This article is based on reporting by Phys.org. Read the original article.
Originally published on phys.org
