"Antarctic Ice Close To Melting Tipping Point"

SYDNEY - A large part of the ice covering West Antarctica could be lost if greenhouse gases in the atmosphere increase only slightly from today's levels and ocean temperatures continue to rise, a study released on Thursday says.

Another related study said if the West Antarctic ice sheet collapsed and the East Antarctic ice sheet continued to melt at its marine margins, global sea level would rise seven meters from today's level.

Antarctica stores about 90 percent of the world's freshwater.

Both studies, published in the journal Nature, are a result of extensive drilling into the seafloor under the Ross Ice Shelf by a team of New Zealand, Italian, American and Germany scientists.

The floating ice shelf won't elevate sea levels if melts because it is already displacing water. The real threat comes when the ice sheet behind, which is below sea level, is exposed to the ocean.

The 50-plus core samples, down to 1.2 kilometers (0.7 mile), allowed the scientists to study how previous periods of rising carbon dioxide affected ocean temperatures, ice movements and sea levels.

The cores showed the West Antarctic ice sheet in the Ross Embayment area collapsed and reformed every 40,000 years. It has collapsed 38 times in the past 5 million years.

"Most of it sits below sea level and is very vulnerable to rising ocean and atmospheric temperatures," Tim Naish, Director of Victoria University's Antarctic Research Center in Wellington, said in a briefing on the drilling study....