Scientists have discovered evidence that Greenland previously melted 400,000 years ago during a moderate warming period — a melting that resulted in sea level rise of five feet or more.
This discovery, presented in a paper published in Science, counters what geologists had previously believed. "We had always assumed that the Greenland ice sheet formed about two and a half million years ago—and has just been there this whole time and that it's very stable," says study co-author Tammy Rittenour. "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."
The finding has implications for the future of Greenland — and the planet at large — as climate change continues to melt massive stores of ice around the globe. By providing evidence that the Greenland ice sheet has melted once before in response to warmer temperatures, the paper’s authors posit that we can expect similar results in the near future.
"Greenland's past, preserved in 12 feet of frozen soil, suggests a warm, wet, and largely ice-free future for planet Earth," says study co-author Paul Bierman.
The research team made their unique discovery by studying a twelve-foot-long tube of soil and rock with a dramatic past. During the cold war, a secret U.S. military base named Camp Century was stationed in northwestern Greenland, with the goal of building an extensive tunnel system in which they’d hide hundreds of nuclear missiles beneath the ice near the Soviet Union, while under the guise of a scientific research project. The military efforts of “Project Iceworm” failed, but the scientific research done as a cover for the operation produced the Camp Century ice core — twelve feet of sediment extracted from beneath more than a mile deep of ice.
And it gets weirder: in subsequent decades, the ice core was moved several times, eventually becoming lost and forgotten. Then, in 2017, the samples were accidentally rediscovered during a move. During a workshop in which scientists from around the globe conducted initial analyses of the rediscovered samples, Bierman described them as potentially being “the key, the Rosetta Stone” that helps researchers understand Greenland’s geologic past.
Following the workshop, an international team got to work conducting in-depth analyses of the samples. Rittenour’s lab at Utah State University examined the “luminescence signal” which reveals the last time that sediments were exposed to the sun. Bierman’s lab at University of Vermont narrowed down these results by analyzing the isotopes found in pieces of quartz from within the core.
The fragile nature of Greenland’s ice sheet has drastic implications for people around the globe. "If we melt just portions of the Greenland ice sheet, the sea level rises dramatically," says Rittenour. "Forward modeling the rates of melt, and the response to high carbon dioxide, we are looking at meters of sea level rise, probably tens of meters.”
Bierman adds on, "Four-hundred-thousand years ago, there were no cities on the coast.”
Sources: Science; Phys.org; University of Vermont
