WASHINGTON (AP) – Low-lying communities like New Orleans and Miami could face increasing peril as melting polar ice raises the ocean to levels not seen in thousands of years.

By the end of this century, Arctic temperatures could reach as high as 130,000 years ago, when the oceans were 13 to 20 feet higher than now, according to research appearing in Friday’s issue of the journal Science.

That doesn’t mean the water would rise that much by 2100 – more likely three feet or so, the researchers say. But it would launch a process that would continue for long after, and even three feet could affect populated areas around the planet and increase the potential damage from storms.

The principal findings:

• At the current warming rate, Earth’s temperature by 2100 will probably be at least 4 degrees warmer than now, with the Arctic at least as warm as it was 130,000 years ago, reports a research group led by Jonathan T. Overpeck of the University of Arizona.

• Computer models indicate that warming could raise the average temperature in parts of Greenland above freezing for multiple months and could have a substantial impact on melting of the polar ice sheets, says a second paper by researchers led by Bette Otto-Bliesner of the National Center for Atmospheric Research. Melting could raise sea level one to three feet over the next 100 to 150 years, she said.

• And a team led by Goeran Ekstroem of Harvard University reported an increase in “glacial earthquakes,” which occur when giant rivers of ice – some as big as Manhattan – move suddenly as meltwater eases their path. That sudden movement causes the ground to tremble.

Otto-Bliesner and Overpeck wrote separate papers and also worked together, studying ancient climate and whether modern computer climate models correctly reflect those earlier times. That allowed them to use the models to look at possible future conditions. The researchers studied ancient coral reefs, ice cores and other natural climate records.

“Although the focus of our work is polar, the implications are global,” Otto-Bliesner said. “These ice sheets have melted before and sea levels rose. The warmth needed isn’t that much above present conditions.”

According to the studies, increases in greenhouse gases in the atmosphere over the next century could raise Arctic temperatures as much as 5 to 8 degrees.

The warming could raise global sea levels by up to three feet this century through a combination of thermal expansion of the water and melting of polar ice, Overpeck and Otto-Bliesner said.

Michael Oppenheimer of Princeton University, who was not part of the research teams, said, “One point stands out above all others and that is that a modest global warming may put Earth in the danger zone for a major sea level rise due to deglaciation of one or both ice sheets.”

Ekstroem and colleagues reported that glacial earthquakes in Greenland occur most often in July and August and have more than doubled since 2002.

“People often think of glaciers as inert and slow-moving, but in fact they can also move rather quickly,” Ekstroem said. “Some of Greenland’s glaciers, as large as Manhattan and as tall as the Empire State Building, can move 10 meters in less than a minute, a jolt that is sufficient to generate moderate seismic waves.”

Melting water from the surface gradually seeps down, accumulating at the base of a glacier where it can serve as a lubricant allowing the ice to suddenly move downhill, the researchers said.

“Our results suggest that these major outlet glaciers can respond to changes in climate conditions much more quickly than we had thought,” said team member Meredith Nettles of Columbia University’s Lamont-Doherty Earth Observatory.

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On the Net:

Science: http://www.sciencemag.org

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