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.
Already changes are being seen in Greenland, where glaciers are sliding into the sea at an alarming rate, reports CBS correspondent Jerry Bowen.
Most troubling, Bowen reports, is that the changes are caused by just a one- or two-degree increase. But, that's the difference between freezing and melting.
These melting glaciers are adding more water to the sea, Bowen reports, and sea levels are rising far faster and sooner than expected. According to another new study, every 40 hours, Greenland pours as much water into the ocean as Los Angeles uses in an entire year. And it is one more finding that has scientists recalculating the day when sea levels may threaten the world's coastal population centers.
That doesn't mean the water would rise 20 feet by 2100. It's more likely to be 3 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:
"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.