www.news.nationalgeographic.com By Warren Cornwall 4 Dec 2014
Melting Antarctic glaciers that are large enough to raise worldwide sea level by more than a meter are dropping a Mount Everest’s worth of ice into the sea every two years, according to a study released this week.
A second study, published Thursday in the journalScience, helps explain the accelerating ice melt: Warm ocean water is melting the floating ice shelves that hold back the glaciers.
The two new pieces of research come as officials of the World Meteorological Organization announcedWednesday that 2014 is on track to be the warmest year on record.
Scientists have long worried that the West Antarctic ice sheet is a place where climate change might tip toward catastrophe. The ice sheet holds enough water to raise sea level by 16 feet (5 meters). The region along the Amundsen Sea is the sheet’s soft underbelly, where the ice is most vulnerable. (See “Rising Seas” in National Geographic magazine.)
Earlier this year, researchers at the University of California, Irvine and NASA’s Jet Propulsion Laboratory reported that the glaciers flowing into the Amundsen Sea—notably the Pine Island and Thwaites Glaciers—were already doomed to collapse, and at the current rate of melting would be gone in 200 years. A study released Tuesday by members of the same team, published in Geophysical Research Letters, confirms those troubling measurements with ones made by other researchers using a total of four different techniques.
The study shows that ice loss from the Amundsen Sea glaciers has accelerated sharply over the past two decades. Between 2003 and 2011 it averaged an eye-popping 102 billion metric tons every year. Mount Everest—rocks, ice, and all—weighs approximately 161 billion metric tons. (See also West Antarctica Glaciers Collapsing, Adding to Sea-Level Rise.)
The decline is driven less by melting on the surface or changes in snowfall, and more by a speeding up of the glaciers’ journey to the ocean, the scientists concluded. In some cases, glaciers reached speeds of more than a third of a mile in a year as they approached the Amundsen Sea, where they either merge into a floating ice shelf, or fall into the water and become icebergs.
The momentum behind this moving ice means the glacier loss is unlikely to stop any time soon, said University of California, Irvine geophysicist Isabella Velicogna, one of the authors of the new study. Velicogna likened the process to a ball at the top of a hill. “Once you give the first push, the ball just keeps rolling,” she said. Click here to read more.