Greenland was still partially ice-free “recently” – and is now also sensitive to climate change

Northwest Greenland was free of ice 400,000 years ago – sooner than previously thought. When the amount of carbon dioxide in the atmosphere was relatively low, the ice caps melted, causing sea levels to rise by at least one and a half meters worldwide. who appears from research That’s Thursday Sciences Back.

“The classic picture was that Greenland always looked the same 1.1 million years ago,” says climatologist Rodrik van de Waal of Utrecht University. He did not participate in the investigation. But because of research after drilling the ice core, that picture has changed in the past 10 years. This study provides direct evidence and now shows that no significant changes in climate are needed to melt the ice caps in Greenland.”

Hundreds of nuclear bombs

Researchers at the University of Vermont have gained access to a special ice core: it was drilled by the US military in the 1960s. It was part of the secret.Ice Worm Project, with the United States attempting to store hundreds of nuclear bombs in tunnels under Greenland during the Cold War. That failed, because the tunnels were unstable.

Scientists were initially interested in the ice cores, but interest waned as the ice cores became newer and deeper. After a few moves, the monsters fell into oblivion, until they were rediscovered in 2018 when dug up in freezers at the University of Copenhagen. Research groups around the world soon sprang up to study them using modern technology. Because not only the ice itself was stored, but also the sediments under the ice caps.

US researchers have now measured “luminescence signals” in the sediments. Minerals that have been stacked under ice for thousands of years absorb many free electrons over time. When the minerals are exposed to sunlight again, they lose those molecules again. With the new measurement methods, it was possible to determine when the sediments were last exposed to sunlight: about four hundred thousand years ago.

For thousands of years, less ice has been added to the cap than has gone away

Our study provides the first direct evidence that northwest Greenland was ice-free at that time. This allowed us to model what smaller size the entire ice sheet should be,” says Paul Berman, a professor of geomorphology at Vermont and lead author of the study.

At the time of the melt, during the interglacial ice age, the climate was hardly warmer than it is today, and carbon dioxide was₂The content in the atmosphere was much lower. The ice caps were out of balance, as they are now: ice formation due to precipitation was slower than melting. Because this situation persisted for 30,000 years, much of Greenland’s caps melted. This contributed to a one and a half meter rise in sea level, by at least six meters in that period. Berman: “If we continue to emit carbon, Greenland’s ice will melt as it did four hundred thousand years ago.”

A better understanding of changes in the Greenland ice sheet is urgently needed, according to van de Waal, “because the prospects for Greenland are not very good.” However, this study does not provide an immediate answer for how quickly the ice sheet will melt in the future, he says. “But the fact that fairly subtle climate changes could seem to be enough to make Greenland ice-free is worrying given the massive changes we’re seeing now.”