Greenland and Antarctica lose 12.5 trillion tons of ice since 1979, study finds
A major scientific assessment finds the polar ice sheets have shed 12.5 trillion tons of ice since 1979, raising sea levels by about an inch.
The Greenland and Antarctic ice sheets have lost roughly 12.5 trillion tons (11.3 trillion metric tons) of ice since 1979, enough frozen water to cover the continental United States in a layer five feet deep, according to a new international study published in the journal Scientific Data.
The melted ice has added about an inch (3.1 centimetres) to global sea levels over the period, on top of other climate-related factors driving ocean heights upward. The assessment, led by the European Space Agency and involving polar scientists from multiple institutions, combined NASA satellite records with European data to extend the measurement of ice sheet volumes back to 1979 for Antarctica and 1972 for Greenland.
Researchers found that the two ice sheets were relatively stable through the 1970s, 1980s and into the 1990s, before melt began and then accelerated sharply during the 2010s. Inès Otosaka, an ice scientist at Northumbria University who led the study, said satellite observations show a clear trend of increasing mass loss decade by decade, particularly in the ice discharged into the ocean, and that the link to climate change is evident as warming air and ocean temperatures drive the losses.
The study attributes the bulk of the melt to dynamic processes rather than rising air temperatures alone. About 84 per cent of the combined ice loss from Greenland and Antarctica comes from increased ice discharge into the oceans, caused by warmer waters eroding the ice sheets from below and at their margins, while surface processes account for the remaining 16 per cent. The authors said this is the first time that proportion has been quantified.
Co-author Eric Rignot, an ice scientist at the University of California Irvine, said the ice sheets are melting away fast and that the loss of polar ice is raising sea levels worldwide, increasing the vulnerability of coastal regions.
The consequences for coastal populations are significant even if the total rise appears modest. Otosaka noted that for every centimetre of sea level rise, another two to three million people face the risk of annual coastal flooding. She also pointed to Greenland's Jakobshavn glacier, which is now retreating by as much as 164 feet (50 metres) a day.
The study notes that the rate of acceleration appeared to pause between 2020 and 2023, but the authors attribute this to short-term weather variations rather than a change in the long-term trend. Otosaka said that although the study used data up to 2023, more recent measurements show the accelerating trend has resumed.
Much of Antarctica's apparent stability stems from record snowfall in East Antarctica, which offset rapid melting in the less stable West Antarctic Ice Sheet. The authors warn that the dynamic processes driving most of the loss are abrupt and active, and are the kind that can trigger runaway tipping points. Co-author Andrew Shepherd, also of Northumbria University, said the changes are tracking decades behind global warming, meaning they can be expected to continue for decades even if planetary heating is halted.