Greenland was ice-free. Scientists worry it could be again

For a period about a million years ago Greenland wasn’t covered in ice. Researchers say the discovery suggests it’s possible the ice sheet could go away again.

Before now, scientists didn’t know whether Greenland’s ice sheet was so stable that it would just weather any climate changes, or if there were ever a period in which Greenland was, if not verdant, at least a bit rocky.

“We shouldn’t count on that ice sheet never melting again.”

A new analysis of rock samples suggests it was largely ice-free, perhaps for as long as 250,000 years.

Scientists were able to determine this because the bare rock during that time was exposed to cosmic rays in the atmosphere, says Marc Caffee, professor of physics and astronomy at Purdue University.

“We now have pretty conclusive evidence that for a time that ice wasn’t there,” Caffee says. “That’s big. That’s new. It’s probably not much different in temperature now than it was then, so we shouldn’t count on that ice sheet never melting again.”

Oceans could rise 20 feet

The Greenland ice sheet is the second largest ice cube on the planet, after the Antarctic ice sheet. If the Greenland ice sheet were to melt—if it is even possible for the ice sheet to melt—then it’s also possible that the planet’s oceans might rapidly rise five or six meters, or more than twenty feet, and wreak havoc on coastal cities worldwide.

Extent of surface melt over Greenland’s ice sheet
Extent of surface melt over Greenland’s ice sheet on July 8 (left) and July 12 (right). Measurements from three satellites showed that on July 8, about 40 percent of the ice sheet had undergone thawing at or near the surface. In just a few days, the melting had dramatically accelerated and an estimated 97 percent of the ice sheet surface had thawed by July 12. In the image, the areas classified as “probable melt” (light pink) correspond to those sites where at least one satellite detected surface melting. The areas classified as “melt” (dark pink) correspond to sites where two or three satellites detected surface melting. The satellites are measuring different physical properties at different scales and are passing over Greenland at different times. As a whole, they provide a picture of an extreme melt event about which scientists are very confident. (Credit: Nicolo E. DiGirolamo, SSAI/NASA GSFC, and Jesse Allen, NASA Earth Observatory)

Caffee’s lab made the discovery by looking at rock samples that were recovered from beneath nearly two miles of ice in 1993. The researchers used a gas-filled magnet attached to a particle accelerator that is sensitive enough to detect the beryllium-10 and aluminum-26 atomic isotopes. These isotopes had been created by the cosmic rays striking the rock and had been hiding beneath the ice for more than a million years.

They report the results in Nature. Joerg Schaefer, a paleoclimatologist at Columbia University and the paper’s lead author, says it’s possible the Greenland ice sheet could go away again.

“Unfortunately, this makes the Greenland ice sheet look highly unstable,” says Schaefer. “With human-induced warming now well underway, loss of the Greenland ice has roughly doubled since the 1990s; during the last four years by some estimates, it shed more than a trillion tons [of ice].”

Coauthors are from Penn State University; the University of California-Berkeley; the University at Buffalo; and the US Army Cold Regions Research and Engineering Laboratory.

Source: Purdue University