An ice shelf in Antarctica, which partially collapsed in 2002, is quickly shrinking and could be gone within a decade.
A team led by Ala Khazendar of NASA's Jet Propulsion Laboratory (JPL), found the remnant of the Larsen B Ice Shelf is flowing faster than before, developing large cracks and becoming increasingly splintered. Two of the tributary glaciers that feed Larsen B also are flowing faster and thinning rapidly.
"These are warning signs that the remnant is disintegrating," said Khazendar, whose team's work on the health of the Larsen B remnant has been published online in the journal Earth and Planetary Science Letters.
"Although it's fascinating scientifically to have a front-row seat to watch the ice shelf becoming unstable and breaking up, it's bad news for our planet," he said. "This ice shelf has existed for at least 10,000 years, and soon it will be gone."
The ice loss in Antarctica is among the clearest signs yet that global warming is already having a devastating impact on the planet. Most scientists blame the rising greenhouse gas emissions and subsequent rise in temperatures on unchecked burning of fossil fuels like oil and coal.
The Antarctic Peninsula is one of the fastest warming regions on Earth, with a temperature rise of 2.5 degrees C over the last 50 years. Along with Larsen B's troubles, scientists from the British Antarctic Survey earlier this week concluded another ice shelf - Larsen C - was melting from above and below, indicating it is being hit by warming surface and ocean temperatures.
Losing these ice shelves could have a cascading effect, since scientists see them as gatekeepers in this frigid region. Without them, glacial ice enters the ocean faster and accelerates the pace of global sea level rise. A study also out this week concluded rates of sea level rise were increasing, mostly due to melting ice in Greenland and West Antarctica.
Khazendar's team used data on ice surface elevations and bedrock depths from instrumented aircraft participating in NASA's Operation IceBridge, a multiyear airborne survey campaign that provides unprecedented documentation annually of Antarctica's glaciers, ice shelves and ice sheets. Data on flow speeds came from spaceborne synthetic aperture radars operating since 1997.
Located on the coast of the Antarctic Peninsula, the Larsen B remnant is about 625 square miles (1,600 square kilometers) in area and about 1,640 feet (500 meters) thick at its thickest point. Its three major tributary glaciers are fed by their own tributaries farther inland.
The estimate of the ice shelf's life span was based on predictions that a huge, widening rift has formed near the ice shelf's grounding line and will eventually crack all the way across. The free-floating remnant would then shatter into hundreds of icebergs that would drift away.
"What is really surprising about Larsen B is how quickly the changes are taking place," Khazendar said. "Change has been relentless."
The remnant's main tributary glaciers are named Leppard, Flask and Starbuck -- the latter two after characters in the novel Moby Dick. The new study finds that Leppard and Flask have thinned by 65 to 72 feet and accelerated considerably in the intervening years. The fastest-moving part of Flask Glacier had accelerated 36 percent by 2012 to a flow speed of 2,300 feet (700 meters) a year -- comparable to a car accelerating from 55 to 75 mph.
"This study of the Antarctic Peninsula glaciers provides insights about how ice shelves farther south, which hold much more land ice, will react to a warming climate," said JPL glaciologist Eric Rignot, a co-author of the paper.