Larsen B ice shelf breaks off from Antarctic Peninsula.

• Author: Larson, Vanessa
• Position: Environmental Intelligence

Over a five-week period ending in March, an ice shelf 200 meters thick and bigger than Luxembourg broke off from the Antarctic Peninsula and fragmented, releasing approximately 720 million tons of floating ice into the Weddell Sea. Scientists estimate that the Larsen B ice shelf was at least 400 years old and may have even existed since the end of the last ice age 12,000 years ago.

The smaller, neighboring Larsen A shelf broke off in 1995, and scientists at the British Antarctic Survey predicted then that Larsen B would also eventually collapse. But the scale and speed of its breakup was "unprecedented," according to Ted Scambos, a glaciologist at the U.S.-based National Snow and Ice Data Center. The center called the demise of the Larsen B shelf "the largest single event in a 30- year series of ice shelf retreats in the peninsula."

Scambos and his colleagues theorize that the melted water collecting on the surface of ice shelves drains into cracks and causes fracturing, which can lead eventually to...