LOS ANGELES - Global warming will melt all the ice in the Arctic Ocean every summer, raising earth temperatures even further, researchers at the University of California-Los Angeles (UCLA) warned.

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The findings, available online Sunday in the April issue of Earth and Planetary Science Letters, a leading journal in geoscience, were based on analysis of the fossilized remains of four-million-year-old mollusks, they said.

Two novel geochemical techniques used to determine the temperature at which the mollusk shells were formed suggest that summertime Arctic temperatures during the early Pliocene epoch (3.5 million to 4 million years ago) may have been a staggering 18 to 28 degrees Fahrenheit warmer than today, the researchers said.

And these ancient fossils, harvested from deep within the Arctic Circle, may have once lived in an environment in which the polar ice cap melted completely during the summer months, according to the researchers.

Such balmy polar weather would certainly melt all the ice in the Arctic Ocean every summer, said Aradhna Tripani, an assistant professor at the UCLA's departments of Earth and space sciences.

"Our data from the early Pliocene, when carbon dioxide levels remained close to modern levels for thousands of years, may indicate how warm the planet will eventually become if carbon dioxide levels are stabilized at the current value of 400 parts per million," she said.

The earth's temperature was raised five to nine degrees Fahrenheit merely by the absence of year-round Arctic ice, according to Tripani.

The results of the study lend support to assertions made by climate modelers that summertime sea ice may be eliminated in the next 50 to 100 years, which would have far-reaching consequences for Earth's climate, she said.

"The Intergovernmental Panel on Climate Change identifies the early Pliocene as the best geological analog for climate change in the 21st century and beyond," said Tripati. "The climate-modeling community hopes to use the early Pliocene as a benchmark for testing models used for forecasting future climate change."