W. Antarctic melt to have big impact on rising sea

A seal swims by icebergs off the British Antarctic Survey's Rothera base January 23, 2009.

LONDON (Reuters) - Melting ice in West Antarctica could add tens of centimeters to rising sea levels over the next century, according to a report by the Scientific Committee on Antarctic Research (SCAR) on Tuesday.

Global sea levels are estimated to rise by a total of 1.4 meters (4 feet 7 inches) by 2100.

"We can see the West Antarctic glaciers are shrinking at a rate fast enough to contribute to a sea level rise of 1.4 m by 2100 but it will be no more than that," SCAR executive director Colin Summerhayes told reporters at a media briefing in London.

"We are ruling out some of the more extreme sea level rises (forecast) for the next 100 years. Those are unrealistic in light of all we know about ice shelves."

A U.N. Intergovernmental Panel on Climate Change (IPCC) report in 2007 forecast a sea level rise of 18-59 cms (7-24 inches) by 2100 but did not take into account the possible increasing melt of Greenland and Antarctica.

A study last week forecast global sea levels to rise by up to 2 meters by 2100.

The 400-page SCAR report is based on evidence from 100 scientists from 13 countries and is the first comprehensive review of the impact of rapid global warming on Antarctica.

Published on the 50th anniversary of the Antarctic Treaty to safeguard Antarctica as a peaceful international space, the report comes six days before the start of a U.N. summit in Copenhagen where world leaders hope to thrash out a new climate treaty.

OZONE HOLE

A hole in the ozone layer has protected much of Antarctica from the effects of global warming, but 90 percent of glaciers along the Antarctic Peninsula have been lost, the report found.

Sea ice has actually increased by 11 percent around the Antarctic since 1980 due to stronger winds, changes in atmospheric circulation and the isolating effect of a hole in the ozone layer.

However, sea ice is declining around the Antarctic Peninsula as stronger winds bring warm, wet air into the region. Warmer water heats glaciers from underneath, causing them to break up.

By the late 21st century, greenhouse gases are expected to double while the ozone hole should heal. The net effect will be strengthening winds and sea ice will decrease by a third.

"Over the next 100 years sea ice is going to decrease. Ice is increasing at the moment but it won't be like that when the ozone hole goes and we will lose 33 percent of sea ice," Summerhayes said.

One effect will be on the ocean's ecosystem. Krill, a food source for penguins, whales and fish, will likely halve.

Corals, algae and other species could become extinct as they fail to adapt to warmer sea temperatures and increased ocean acidity. Alien species could thrive and invaders, such as stone crabs from South America, could severely impact the ecosystem.

(Editing by Sue Thomas)