New computer modeling suggests the Arctic Ocean may be nearly ice-free in the summertime as early as 2014, Al Gore said Monday at the UN climate conference.

This new projection, following several years of dramatic retreat by polar sea ice, suggests that the ice cap may nearly vanish in the summer much sooner than the year 2030, as was forecast by a US government agency eight months ago.

One US government scientist Monday questioned the new prediction as too severe, but other researchers previously have projected a quicker end than 2030 to the Arctic summer ice cap.

"It is hard to capture the astonishment that the experts in the science of ice felt when they saw this," said former US Vice President Gore, who joined Scandinavian officials and scientists to brief journalists and delegates. It was Gore's first appearance at the two-week conference.

The group presented two new reports updating fast-moving developments in Antarctica, the autonomous Danish territory of Greenland, and the rest of the Arctic.

"The time for collective and immediate action on climate change is now," said Denmark's foreign minister, Per Stig Moeller.

But delegates from 192 nations were bogged down in disputes over key issues. This further dimmed hopes for immediate action to cut more deeply into global emissions of greenhouse gases.

Gore and Danish ice scientist Dorthe Dahl Jensen clicked through two slide shows for a standing-room-only crowd of hundreds in a side event at the Bella Center conference site.

One report, on the Greenland ice sheet, was issued by the Arctic Monitoring and Assessment Program, an expert group formed by eight Arctic governments, including the United States. The other, commissioned by Gore and Norway's government, was compiled by the Norwegian Polar Institute on the status of ice melt worldwide.

Average global temperatures have increased 0.74 degrees C (1.3 degrees F) in the past century, but the mercury has risen at least twice as quickly in the Arctic. Scientists say the makeup of the frozen north polar sea has shifted significantly in recent years as much of the thick multiyear ice has given way to thin seasonal ice.

In the summer of 2007, the Arctic ice cap dwindled to a record-low minimum extent of 4.3 million square kilometers (1.7 million square miles) in September. The melting in 2008 and 2009 was not as extensive, but still ranked as the second- and third-greatest decreases on record.

Last April, the US National Oceanic and Atmospheric Administration predicted that Arctic summers could be almost ice-free within 30 years, not at the 21st century's end as earlier predicted.

Gore cited new scientific work at the US Naval Postgraduate School, whose Arctic ice research is important for planning polar voyages by Navy submarines. The computer modeling there stresses the "volumetric," looking not just at the surface extent of ice but its thickness as well.

"Some of the models suggest that there is a 75 percent chance that the entire north polar ice cap during some of the summer months will be completely ice-free within the next five to seven years," Gore said. His office later said he meant nearly ice-free, because ice would be expected to survive in island channels and other locations.

Asked for comment, one US government scientist questioned what he called this "aggressive" projection.

"It's possible but not likely," said Mark Serreze of the US National Snow and Ice Data Center in Boulder, Colorado. "We're sticking with 2030."

On the other hand, a leading NASA ice scientist, Jay Zwally, said last year that the Arctic could be essentially ice-free within "five to less than 10 years."

Meanwhile, what's happening to Greenland's titanic ice sheet "has really surprised us," said Jensen of the University of Copenhagen.

She cited one huge glacier in west Greenland, at Jakobshavn, that in recent years has doubled its rate of dumping ice into the sea. Between melted land ice and heat expansion of ocean waters, the sea-level rise has increased from 1.8 millimeters a year to 3.4 millimeters (.07 inch a year to .13 inch) in the past 10 years.

Jensen said the biggest ice sheets — Greenland and West Antarctica — were already contributing 1 millimeter (.04 inch) a year to those rising sea levels. She said this could double within the next decade.

"With global warming, we have woken giants," she said.