Meltdown

An illustrated guide to our collapsing Antarctic glaciers

May 16, 2014
Obsession
The Sea
May 16, 2014

Structurally critical glaciers from the West Antarctic ice sheet are disappearing way faster than we realized, two teams of scientists recently reported.

Their papers—one from NASA and the University of California, Irvine, the other from the University of Washington—both say there’s nothing we can do to stop it.

Here’s how the glaciers in question will collapse.

Tap image to zoom
(NASA.gov)

Topography

The West Antarctic ice sheet is located about 1,000 km (600 miles) southeast of Argentina’s southern tip. The bulk of it sits in a bowl-shaped bed of underwater land. But not all of it. Gravity’s pull yanks a steady flow of the glacial ice loose from the land, forming what’s called an “ice shelf.” This floating extension of the glacier extends into the sea, and as it builds up, actually helps hold back the mass of ice still standing on the land behind it.

Tap image to zoom
This cross-section shows the undersea massif beneath the West Antarctic ice shelf. Pink=areas uncovered by ice; teal=ice shelf; blue=ice sheet, with shades representing 1,000m gradations of thickness.(Screenshot from presentation: "Recent Changes in Greenland & Antarctica," Joughin & Poinar)

Warming seas

Warming seas thin the ice shelf, lightening its load so that it’s even more buoyant. This is a natural phenomenon; Antarctic winds whip up naturally warmer water from the ocean’s depths, lapping away at the ice shelf as a roughly equal amount of snowfall replaces what’s melted.

Tap image to zoom
(Screenshot from presentation: "Recent Changes in Greenland & Antarctica," Joughin & Poinar)

Thinning, floating and melting

But scientists think that rising sea temperatures are now eroding the ice shelf faster than the snow can rebuild it. Intensifying southern sea wind forces—likely a product of climate change—also exacerbate ice erosion (pdf, p.1,141). The lighter the ice shelf becomes, the more of it starts floating, exposing more ice to water. That process pushes the “grounding line”—the point where the ice separates from land and begins to float—further inland.

Tap image to zoom
(Jet Propulsion Laboratory, California Institute of Technology)

As the “grounding line” retreats, the “ice shelf” supports less and less of the frozen mass behind it, causing more and more of that ice to flow into the sea.

Tap image to zoom
From 1996 to 2011, Smith Glacier’s “grounding line” retreated 35 km.(Screengrab from NASA/GSFC/SVS)

Over the hump

Thanks to the under-sea topography on which the West Antarctic ice shelf sits, this process is about to get a whole lot faster. That’s because the water is eating away at the ice quite close to the lip of a bowl-shaped undersea basin. Once the water gets over that hump, more ice will be exposed to it, kicking the whole melting process into a higher gear. “All of our simulations show it will retreat at less than a millimeter of sea level rise per year for a couple of hundred years, and then, boom, it just starts to really go,” says Ian Joughin, professor at the University of Washington and co-author of that team’s paper.

Tap image to zoom
What happens when the a glacier’s “grounding line” retreats past the edge of the sea valley.(Created from presentation: "Recent Changes in Greenland & Antarctica," Joughin & Poinar)

Inevitable, but not necessarily soon

Don’t ditch beachfront real estate just yet; it’ll be at least two centuries before the actual collapse of the West Antarctic glaciers scientists are studying. (And it may be as long as 1,000 years.) But when they do go, the repercussions will be real. Scientists say the collapse of six vulnerable glaciers could boost global sea levels by 4 feet (1.2 meters). Their disappearance will also destabilize the rest of the West Antarctic ice sheet. And if that collapses, scientists say sea levels will surge between 11 and 16 feet, enough to engulf chunks of the Netherlands, Vietnam, Bangladesh and the southern United States, to name just a few places.

Tap image to zoom
Areas that would be inundated if sea levels rose around 5 meters marked in yellow.(Image generated by University of Arizona, Department of Geosciences digital elevation model)

Top News

Powered by WordPress.com VIP