WASHINGTON: A mile-thick ice sheet in Greenland vanished around 416,000 years ago during a period of moderate natural warming, driving global sea rise to levels that would spell catastrophe for coastal regions today, a study said on Thursday.

The results overturn a long-held view that the world’s largest island was an impregnable fortress of ice over the past 2.5 million years, and instead show it will be far more vulnerable to human-caused climate change than previously thought. “If we want to understand the future, we need to understand the past,” University of Vermont scientist Paul Bierman, who co-led the paper published in Science, said.

The research relied on an ice core extracted 4,560 feet under the surface of Northwest Greenland by scientists at Camp Century, a secretive US military base that operated in the 1960s. This 12-foot long tube of soil and rock was lost in a freezer only to be rediscovered in 2017.

Scientists were stunned to learn it contained not just sediment but leaves and moss — irrefutable evidence of an ice-free landscape, perhaps covered by an ancient forest that woolly mammoths would have roamed.

Though researchers were deprived for decades of access to the precious sample, Bierman said in some ways it was “providential,”. Key among the methods is “luminescence dating,” which allowed scientists to determine the last time that sediment buried beneath the Earth’s surface was exposed to light.

“As sediment is buried beneath the surface, background radiation from soil fills in the little holes or imperfections in minerals like quartz or feldspar, and builds up what we call a luminescence signal over time,” co-author Drew Christ said.

Published in Dawn, July 21st, 2023