Scientists: More Antarctic Ice Shelves Are at Risk

Scientists, still shaken by last week's news that a Rhode Island-sized ice shelf had splintered and sloughed into the sea, warn that more ice break-ups probably lie ahead.

"We just saw how a small amount of warming that doesn't seem like a big deal can cause billions of tons of ice to fragment and disappear," said Ted Scambos, a glaciologist at the National Snow and Ice Data Center. "Now we know there's potential for break-ups to happen rapidly."

The collapse of Antarctica's Larsen B ice shelf led to the disintegration of about 720 billion tons of ice in a 35-day period. In 1995, the northernmost section of the Larsen shelf on the Antarctica Peninsula, known as Larsen A, broke off in a similarly dramatic fashion. Now Scambos is concerned the last remaining and largest section of the shelf, Larsen C, could be next to go.

"Larsen C is the next area to watch," he said, explaining that the Antarctic Peninsula "sticks out like a thumb" in the water and so is more affected by climate change.

Cracking Points

Research has shown that increased temperatures have lengthened the melting season at the Antarctic Peninsula over the past five decades. The warming causes pools of water to melt on the ice's surface during Austral summers and these pools exert pressure on existing cracks on the ice.

"It's like a pane of glass that's shattered and is waiting to be tapped," Scambos said. This mechanism is likely what caused Larsen A and B to crumble and it could soon have the same effect at Larsen C.

Meanwhile, Tim Naish, a New Zealand climate researcher, is focused on a potentially more catastrophic collapse at the continent's Ross Ice Shelf. This western shelf — Antarctica's largest — covers about 332,000 square miles or an area about the size of France. Since much of the shelf sits on the continental shelf and is not already floating, its collapse into the ocean could lead to a potential 15- to 20-foot rise in sea level.

A study released in January revealed the Ross Ice Shelf might have been thickening as several major ice streams increased their flow from the South Pole into the continent's outer ice wedge. But follow-up observations show this flow has slowed or even frozen to a halt in places.

Naish says that slowing could cause the shelf to thin, making it especially vulnerable to collapse.

To some degree iceberg shedding is a natural process in Antarctica. At the continent's center, the weight of piles of ice — in some places a mile thick — provide a constant push downward and outward. The constant nudging causes ice shelves to form at the continent's edges and to eventually break free into the ocean. In the spring of 2000, three major icebergs peeled off the Ross Ice Shelf.

Most researchers agreed the loss of those icebergs was part of a natural cycle. But scientists are only beginning to understand the coldest continent on Earth and what may be its natural ice shedding rate and what may be accelerated.

Continent Coming Into Focus

Until the mid-1990s, vast sections of Antarctica remained unmapped since the territory was too harsh for researchers to record in person. Now a joint project of NASA and the Canadian Space Agency has provided satellite radar maps of the terrain. The maps show a frozen continent that is much more active than researchers had realized.

Energetic ice streams on the continent "drain great volumes of ice — several cubic miles per year — into the sea," observes Kenneth Jezek of Ohio State University's Byrd Polar Research Center.

Scambos says ancient ice core samples, satellite images and last week's dramatically rapid loss of ice at the Larsen Ice Shelf all suggest the continent appears to be losing ice faster than normal.

"If people continue to have the presence we now have, I don't think anything will happen as it did centuries before," said Scambos.

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