In 1959, The United States began building a real-life replica of The Empire Strikes Back’s frozen Echo Base. Camp Century was supposed to test snow tunneling technologies in northwest Greenland, not far from the north pole, for scientific study.

In reality, the US was exercising its military strength and may have been considering Project Iceworm, a plan to conceal 600 nuclear missiles in thousands of kilometers of snow tunnels across northern Greenland, near the former Soviet Union. The island’s huge ice sheet, however, had other plans for Camp Century—ice changes and flows, making this an unsuitable location for storing nukes or running the nuclear reactor that powered the camp.

Iceworm never materialized, and the United States closed Camp Century in 1966, leaving the tunnels to crumble. However, before everyone evacuated, researchers managed to unearth some serious scientific dirt by drilling a 4,550-foot-deep core under the ice sheet. They bore another 12 feet after hitting soil, bringing up a block of frozen sand, nasty ice, cobbles, and mud. In the 1970s, the military transferred the ice core from its own freezers to the University of Buffalo. The core ended up in Denmark in the 1990s, where it was maintained frozen, providing scientists with priceless insight into prior ice ages.

Nobody worried about the sediment until it was rediscovered in cookie jars in a University of Copenhagen freezer in 2018. An international team of experts has now examined that sediment and produced a significant scientific discovery.

“In that frozen sediment are leaf fossils and little bits of bugs and twigs and mosses that tell us in the past there was a tundra ecosystem living where today there’s almost a mile of ice,” says Paul Bierman, a geoscientist at the University of Vermont and coauthor of a new paper describing the discovery published in the journal Science. “The ice sheet is delicate. It has the ability to vanish, and it has done so. We now have a date for that.”

Previously, geologists believed that Greenland froze about 2.5 million years ago and has remained that way ever since. Bierman and his colleagues discovered in 2021 that it had been ice-free for millions of years. They’ve now dated the tundra environment preserved in the Camp Century core to 416,000 years ago, implying that northwestern Greenland couldn’t have been frozen at the time.

Scientists also know that global temperatures at the period were equivalent to or slightly warmer than they are now. However, atmospheric concentrations of planet-warming carbon dioxide were at 280 parts per million at the time, compared to today’s 422 parts per million—a figure that continues to rise. Because humans have substantially and swiftly warmed the climate, we have surpassed the circumstances that previously caused widespread melting of Greenland’s ice sheet and gave rise to the tundra habitat. “It’s a forewarning,” says Tammy Rittenour, a geoscientist at Utah State University and coauthor of the new paper. “This is possible under much lower CO2 conditions than we currently have.”

That melting might be really dangerous. According to the latest study, the Greenland ice melt 400,000 years ago produced at least 5 feet of sea level increase, but maybe as much as 20 feet. “These findings raise additional concerns that we may be dangerously close to the threshold for the collapse of the Greenland ice sheet and massive additional sea level rise of a meter or more,” says Michael Mann, a climate scientist at the University of Pennsylvania who was not involved in the research. Even with the possibility of an additional 20 feet of global sea level rise, less than a foot of global sea level increase is already producing major flooding and storm surge problems for coastal cities.

If Greenland melts again, it might reach a point of no return, driving rising sea levels inexorably. When an ice sheet melts, the darker ground underlying it absorbs more of the sun’s radiation, raising local temperatures and promoting more melting.

“If too much mass is lost and the elevation of the surface drops significantly, the resulting warming of the surface makes regrowth of the ice sheet more difficult,” says Richard B. Alley, a geoscientist at Pennsylvania State University who was not involved in the research. “The new paper adds to the growing body of evidence that even moderate sustained warming will cause significant melting in Greenland, forcing sea-level rise.”

More research is needed to determine how the Greenland ice sheet may decline in the future. Temperatures 400,000 years ago were similar to today’s, but the natural warming that caused Greenland’s melting occurred gradually. Humans have rapidly and severely warmed the earth since preindustrial times, and anthropogenic CO2 will remain in the atmosphere for thousands of years until a large-scale removal method is developed. We can also lower the temperature. Mann believes that if we reduce emissions, Greenland’s ice sheet will remain stable.

A contemporary Greenland tundra landscape JOSHUA BROWN TAKES THE PHOTO
So, how did this research team determine that northwest Greenland had no ice sheets 400,000 years ago? The silt from the Camp Century core was rich in organic material, but it was far too old to study using carbon dating, which can only go back 50,000 years. “We took little twigs and leaves and immediately sent them off for radiocarbon dating, and they came back ‘radiocarbon dead,'” Rittenour explains. “There were no traces of radioactive carbon left in the sample.”

Rittenour instead used light, specifically the luminescence of feldspar particles buried in the sediment. Over time, free electrons accumulate in minerals, resulting in a “luminescence signal.” Sunlight effectively cancels out this signal, but once these minerals were buried behind thousands of feet of ice, the sun’s rays could no longer reach them, and the electron accumulation resumed. Rittenour used infrared light to examine inside the Camp Century samples in a lab darkroom. “We can use one wavelength of light and measure the luminescence coming off at a different wavelength,” Rittenour explains. “The more luminescence produced by an older sample, the more luminescence it produces.” This allowed them to calculate how long it had been since the feldspar in the sediment had been exposed to sunlight.

In addition, Bierman examined the stone quartz in the samples for rare isotopes of beryllium and aluminum at the University of Vermont. “They form when cosmic rays, these extremely high-energy particles, crash into Earth from outside the solar system.” “And every now and then, they’ll smack an element in the quartz grain,” Bierman explains. “We can tell how long something has been buried away from those cosmic rays by looking at the ratio of those two isotopes.” The findings indicated that this debris had been lying on the landscape for less than 16,000 years.

Scientists are racing to dig additional ice cores in Greenland in order to collect more soil. Although the Camp Century core provides a foundation for modeling that can be used to make estimates, more cores will allow them to better determine how much of the island’s ice had vanished and how quickly—and what that might portend for the ice sheet’s present demise. “We now have definitive evidence that the Greenland ice sheet disappears when the climate warms,” adds Bierman. “And we’ve only just started warming the climate.”

“We use the past to try to understand the future and the present,” Bierman says. “And that makes the future a little scary.” Not that we should run from it, but it strikes me as a call to action.”


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