Every year, Greenland sheds more than 250 gigatons of ice – enough to fill the entire state of Texas with over a foot of water. Despite being one-tenth the size of Antarctica, Greenland’s ice sheet is now the single largest contributor to sea-level rise. Even more worrisome, a string of recent studies suggest Greenland’s meltdown is accelerating – troubling news for millions of people living in coastal areas.
Only a tiny fraction of Greenland’s ice was predicted to be released this century, resulting in about 12cm (5in) of sea level rise, according to the latest Intergovernmental Panel on Climate Change report. Because the ice sheet sits on bedrock, Greenland’s thaw was expected to be slow and steady (unlike Antarctica’s ice shelves, which are vulnerable to warmer water below). In the last few years, however, Greenland’s melt has been anything but slow. And scientists aren’t entirely sure why.
Warmer temperatures are a factor, of course. Greenland is about 2C (3.6F) warmer now than just a few decades ago. But that alone doesn’t explain it, at least not fully. “It’s not something that’s predicted in any coupled climate-ice sheet model,” said Jonathan Bamber, a researcher with the University of Bristol who uses remote sensing to track the movement of ice sheets. “None of them reproduce that dramatic acceleration in mass loss that we’re seeing.”
This summer, glaciologists are working across Greenland to figure out why the big ice sheet, which holds more than 6m (20ft)’s worth of sea level rise, is unraveling so quickly. At the East Greenland Ice-Core Project (EGRIP) camp, for example, scientists are sending a giant drill through a mile of snow and ice. Like the rings of a tree, the extracted core can reveal the history of the ice sheet and the climate itself, dating back tens of thousands of years.
It’s the second season of drilling at EGRIP and researchers don’t expect to hit bedrock until the end of next summer. When complete, it will be the sixth such ice core collected from Greenland, and the first to be drilled through an ice stream, which funnels water beneath the ice sheet, pulling with it giant chunks of ice into the ocean.
“It is not well understood right now how the ice is moving and it’s not well incorporated into models,” said Anders Svensson, EGRIP’s operations manager and a geophysicist with the Niels Bohr Institute at the University of Copenhagen, speaking from Greenland on a satellite phone.
Unlike previous drill cores, which were taken near the middle of the ice sheet where the ice layers are the most stable, the EGRIP site is constantly moving. Even the camp itself – a maze of outbuildings and snow trenches, and a rudimentary airstrip – is sliding toward the sea at a rate of about 50m (160ft) a year. That makes drilling challenging, said Svensson.
“But that’s really the main point of being here: to understand the ice dynamics much better,” he said. “It’s been a demand from modelers that we go somewhere where there’s more action and where the ice is actually moving.” The ice core samples will be studied under a microscope to determine how much movement occurred during past warming periods – and how quickly the ice stream might destabilize in the future.
Across the island, in what’s known as the Dark Ice Area of southwest Greenland, researchers are exploring a different cause of melt. The team led by the University of Bristol is looking at how microscopic organic growth on the ice can decrease the surface’s albedo, or reflectivity. “We want to characterize how important that is and how it might change in the future,” said Bamber, who is not part of the field expedition.
The rate of surface melt has been steadily increasing across Greenland since around 1995, but spiked during particularly hot summers in 2010 and 2012, when NASA satellites observed the thaw of nearly the entire surface of the ice sheet. The pulse of meltwater released was so massive it triggered slow-motion waves through the ice sheet, lurching glaciers toward the ocean.
The real worry now, Bamber said, is that as temperatures rise, Greenland’s ice could become even more conducive to biological growth, setting off a dangerous feedback loop by darkening the surface and absorbing more heat. “The thing about Greenland is you’ve got a big area that’s melting already, and as the planet warms that melt is just going to go up and up.”
But could Greenland’s ice – a holdover from the last major ice age – ever disappear entirely? Prior to last year, the answer would have been a cautious “not likely.” A study published in the journal Nature last December, however, suggests that Greenland was nearly ice-free in the not-too-distant part – and that it could happen again.
“It’s not good news,” admits the paper’s lead author, Joerg Schaefer, a paleoclimatologist with the Lamont-Doherty Earth Observatory and a professor at Columbia University.
Researchers analyzed bedrock samples collected from the bottom of an ice core nearly 3km (2 miles) deep that was drilled near the center of Greenland in 1993. Using a new laboratory technique, they found evidence that 1 million years ago the bedrock was bombarded by cosmic rays for an extended time frame. The rays would have been blocked had there been significant ice on top.
“It tells us that the Greenland ice sheet was gone for substantial periods in the very recent geological past,” Schafer explained. That means Greenland’s ice is much less stable than previously thought, which does not bode well for the future, he said.
That same technique will now be applied to other rock samples from across Greenland to reconstruct the pattern and timing of ice retreat during previous melts. It could provide critical information for understanding what lies ahead and for potentially setting up an early warning system.
But the science needs to catch up quickly, Schaefer said. If Greenland’s melt happens sooner than expected, the impacts could be catastrophic. “We have to understand this better and we have to understand this fast,” he said. “We can’t wait another 50 years.”