A CHUNK OF ice the size of lower Manhattan—four miles wide, a mile across, and half a mile thick—broke off of the Helheim Glacier in Greenland and tumbled into the sea a few weeks ago.
When ice that was previously sitting on land, like this piece of the glacier, falls into the ocean and melts, the ocean gets a little fuller. In other words, sea levels rise.
This particular chunk of glacier—about 9 billion tonnes of ice, enough to give every American more than 600 10-pound bags of ice—won't have a noticeable effect on the waves that lap at the beaches in Sydney, Cape Cod, or Honolulu. But when you add up this plus all the other pieces that slough off from both Greenland and West Antarctica each year, the effect adds up: about a millimeter a year, or a few inches over the past 25 years. And the ice sheets shed faster and faster each year.
Where’s the Ice?
Ice sheets, like those in Greenland and Antarctica, lock up about two percent of all the water that exists on the world’s surface (most of the rest, unsurprisingly, is in the ocean). Greenland spits about 245 billion tonnes of ice into the ocean each year—more when it's warmer and a little less during cool years. Antarctica currently dumps about 90 billion tonnes each year, but that number is very likely to increase fast in coming decades.
Most ice in both Greenland and Antarctica spills out into the ocean from just a few spots—so understanding the physics at work at these spots, like the towering ice wall at the bottom of Helheim Glacier, helps scientists understand how and why, exactly, the glaciers lose their ice. And they use that information to figure out how much more ice might be lost in the future.
David Holland, an NYU oceanographer who was perched in a prime viewing spot when the glacier calved, explains that the physics that control both big calving events like this one, or even bigger ones (in 2010, another glacier in Greenland lost a piece about 100 square miles in area), are very similar. From events like these, they can “learn how big things break,” he says, which will tell them how the ice will behave in the future—when the climate is even warmer.
This event in itself isn’t necessarily a harbinger of climate doom. “Calving happens,” says Kristin Poinar, a glaciologist from the University of Buffalo. “Ice isn't a good building material—you could never build a skyscraper out of it because it collapses under its own weight if it's more than 90 meters tall.” And at the very edge of the Helheim Glacier, the wall of ice is about 70 meters (about 230 feet) tall. So pieces break off as a natural part of the glacier mass balance cycle that would happen with or without climate change.
The Great Crack-Up
Denise Holland, the field manager for NYU's Environmental Fluid Dynamics Laboratory, captured the break-up via time-lapse photography on June 22. She and her colleagues had gone to Helheim Glacier, one of the “big 3” glaciers in Greenland where lots of ice flows from land to sea, to study just this kind of crack-up.
Holland and her colleagues set up camp on the side of the rocky fjord that cups the glacier, right where the ice spills off land and meets the sea. They had arrived a few hours earlier, but Holland sets up her camera as soon as she arrives at any new camp, just in case something important happens.
And in the gloaming Greenlandic twilight, at 11:30PM, she heard some loud crackling. “It's a very strange thing to explain,” she says. “It sounded like explosions, that reverberate from one side of the fjord to the other—not like normal ice cracking,” but something bigger, louder, and more dramatic.
She ran to her camera and turned it on. And over the next 35 minutes, she and her colleagues watched in awe as giant ice blocks broke away.
And what they saw, says Holland, was a dramatic encapsulation of how complex the calving process can be. “You see these flat tabular icebergs come off, and pinnacle icebergs come off, some toe first coming up from the bottom, and others slump over and fall into the ocean,” she says.
Understanding the details of how the ice sheets slough off their glaciers is key to understanding how quickly they'll shrink, explains David Holland, an oceanographer at NYU who was also perched in a prime viewing spot for the ice show.
“When you're looking at sea-level rise, the place that matters is West Antarctica,” he says. But it's hard to get down to Antarctica—so the team set up camp in Greenland. “The way to learn about what will happen in West Antarctica is to look at what's happening with the glaciers in Greenland—where things are smaller and happening more rapidly. It's really a window into how sea-level change will happen in the future.”