Climate Change Melts Antarctic Ice Shelves: USGS

Deborah Zabarenko, PlanetArk 23 Feb 10;

WASHINGTON - Climate change is melting the floating ice shelves along the Antarctic Peninsula, giving scientists a preview of what could happen if other ice shelves around the southern continent disappear, the U.S. Geological Survey (USGS) said on Monday.

The ice has retreated so far from the land mass that Charcot Island, which has long been connected to the peninsula by an ice bridge, emerged as a real island again last year, a USGS scientist said.

"This is the first time since people have been observing the area, since the 1800s, that that ice shelf has not hitched together Charcot Island and the peninsula," scientist Jane Ferrigno said in a telephone interview.

The Antarctic Peninsula extends further northward than the rest of the roughly circular ice-covered continent, and it is warmer than the rest of Antarctica. But even in the peninsula's coldest, southern part, ice shelves are vanishing.

Research by the USGS was the first to show that every ice front on the southern section of the peninsula has been retreating from 1947 to 2009, with the most dramatic changes since 1990.

A study of the phenomenon by the USGS in collaboration with the British Antarctic Survey and assistance from the Scott Polar Research Institute and Germany's Bundesamt fur Kartographie and Geodasie was posted at pubs.usgs.gov/imap/i-2600-c/ in February; a statement was released on Monday.

ICE SHELVES ACT AS GLACIER DAMS

Ice shelves act as dams to keep land-based glaciers from flowing unimpeded into the sea; when ice shelves melt, glaciers can move more quickly into ocean waters.

If all the land-based ice in Antarctica melted, scientists have estimated sea levels worldwide could rise from 213 to 240 feet, according to the study. If just the ice in West Antarctica melted, there would be a sea level rise of about 20 feet, threatening coastal communities and low-lying islands.

The land-based ice on the Antarctic peninsula is not enough to fuel a major rise in sea level, Ferrigno said. However, the dramatic disappearance of ice shelves there could give a clue of what could happen when glaciers are free to flow seaward.

This is important because the Antarctic ice sheet contains 91 percent of Earth's glacier ice, Ferrigno said.

Unlike Antarctic land-based ice, the ice that covers much of the Arctic Ocean would not contribute to sea level rise if it all melted, in much the way that a melting ice cube in a glass of water would not make the glass overflow.

But both the Arctic and Antarctic have major impact on weather in the temperate parts of the world.