How Water Is Cracking Up Antarctica

Mark Fahnestock of the University of Maryland studied two decades of satellite images of the area and found a key correlation between "ponds" of melted ice and the breakup of the Larsen Ice Shelf. The ice broke up the most during years with a lot of melting.

In 1995, when a 775-square-mile chunk of the ice shelf broke off during a violent storm, the "melt season" lasted 80 days, which was 20 days longer than normal, Fahnestock found.

So what appears to be happening is that rising summertime temperatures cause surface ice to melt, flooding cracks and wedging apart the ice. All it takes is a storm, or a nudge from a drifting chunk of ice, to break off a piece.

Hemming in the Continent

The loss of the Larsen shelf in itself is not all that important, unless you happen to be aboard a ship that has to dodge icebergs in the area, but the finding holds profound implications for the rest of Antarctica.

Researchers at Pennsylvania State University, for example, have shown that the huge shelves of floating ice along Antarctica's coast serve a very useful purpose. In effect, they hold back the glaciers on the mainland, providing a "braking system" that keeps the glaciers from sliding into the sea.

That hasn't been much of a problem along the peninsula, because the glaciers there are wedged in mountain valleys and even with the loss of the braking system, it's hard for them to move very fast. And they are smaller glaciers, at least for Antarctica, so their contribution to sea level rise would be inconsequential, Scambos says.

Not too far away, however, is the Ross Ice Shelf, a humongous chunk of ice that holds back giant glaciers that rest on mud. If the Ross were to disintegrate, those glaciers could slide into the sea, although that could take several decades.

Scientists estimate that if the landlocked ice in just the Western Hemisphere of Antarctica were to be released into the ocean, the seas would rise about 15 feet around the world.

What are the chances of that happening?

Drip by Drip

If the Ross experiences a summertime warming trend over the next 50 years equal to the warming of the Larsen over the last half century, it could also disintegrate. And, Scambos says, we're talking a couple of degrees, not a heat wave.

Of course, that might not happen. No one knows yet exactly how much warmer Antarctica is likely to get over the next few decades. But one thing is clear. It's changing.

"There's something fundamentally different about climate now than over the last several centuries," Scambos says. "The Larsen Ice Shelf had been there for several centuries," and it broke up almost overnight, geologically speaking.

And other areas of Antarctica "are closer than we thought to undergoing the same thing," he adds.

Lee Dye’s column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.

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