A secret ice core taken from Greenland in the 1960s has revealed that Earth’s ice sheets are less stable and more vulnerable to melting than previously believed.
Greenland’s ice sheet is 3.2 km (2 miles) deep and more than three times the size of France. Scientists are interested in this because its meltwater would raise sea levels by 7 metres (23 feet), putting coastal areas in jeopardy around the world.
Until now, the global scientific community believed Greenland’s ice had been there for around 2.5 million years. “Maybe the edges melted, or with more snowfall, it got a bit fatter — but it doesn’t go away, and it doesn’t dramatically melt back. But this paper shows that it did,” said Tammy Rittenour, study co-author from Utah State.
Indeed, the team, comprising scientists from the Universities of Vermont, Utah State, and fourteen other establishments, has shown the ice sheet melted approximately 416,000 years ago, give or take 38,000 years, enough to allow plant matter in and elemental changes to occur.
It’s really the first bulletproof evidence that much of the Greenland ice sheet vanished when it got warm.
Paul Bierman, the research team’s co-leader from University of Vermont
In the 1960s, Camp Century in northwest Greenland saw a Cold War mission in which the US Army drilled down through 1,390 metres (4560 feet) to extract a twelve-foot-long tube of soil and rock. The block of icy sediment lay forgotten in a freezer for decades. Rediscovered in 2017, studies have now revealed it contains evidence of a landscape free of ice, such as boreal forest.
Thanks to advanced luminescence technology and isotope analysis of rare chemical elements, the researchers calculated that the melting took place in a period called the Marine Isotope Stage 11, around 424,000 to 374,000 years ago. This is concerning because it shows that the ice sheet is far less permanent or stable than previously thought.
The team puts the sea-level rise at the time at between 1.5 and 6 metres (five and 20 feet). Temperatures during the era were similar to or only slightly warmer than those today. Nowadays, the ice sheets’ new-found instability could cause flooding and mass migration on a planetary scale.
Tammy Rittenour, co-author from Utah State, notes that melting today would likely be exacerbated by human-driven climate change, affecting millions of people. “If we melt just portions of the Greenland ice sheet, the sea level rises dramatically,” she said. Among the places at risk she listed: “New York City, Boston, Miami, and Amsterdam. Look at India and Africa — most global population centers are near sea level.”
