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.
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