Oct. 3, 2008 -- Sea ice at the top of the planet has apparently reached the lowest volume ever recorded, say scientists, with conditions declining toward a point where the Arctic Ocean may soon be completely ice-free in summertime.

While final numbers are still coming in, experts at the National Snow and Ice Data Center in Boulder, Colo., believe the overall volume of Arctic sea ice -- determined by measuring the area covered and the thickness of ice -- has reached the lowest level since satellite measurements began in 1979.

"We're pretty confident this is a record low," said Walt Meier, a research scientist at the center.

Meier and his colleagues monitor the health of Arctic sea ice by looking at many factors, including the extent of sea ice -- how much can be seen from space -- and the thickness of ice hidden underwater, to calculate the overall volume.

"It's like a building and a Hollywood set of a building," Meier said. "You take a picture of both of those, and they look exactly the same. But if you go and peer around the corner, one is thick, and one isn't. And so, what we're seeing now is that ice, that used to be like a building, is kind of becoming more like a Hollywood movie set."

Experts say that much of the thicker Arctic sea ice -- which takes years to develop but is more robust -- has been replaced by younger, "first year" ice that is thinner and more prone to melting. In March 2008, data showed that a record 73 percent of the sea ice in the Arctic was made up of the thinner ice.

"The arctic is fundamentally changing in character, and we're going to continue this downward trend and eventually reach the point when we have entire sea-ice melts during the summertime," Meier said.

Experts warn that, without Arctic sea ice, there will be major, if unknown, consequences far beyond the top of the planet. The region acts as a giant air conditioner for the planet, helping stabilize global temperature and weather patterns in lower latitudes, like the jet stream.

"You're changing the equation," Meier said. "And that's going to potentially change traditional wind patterns, ocean currents, and storm tracks. And which way the wind blows has tremendous impact in certain areas, particularly on where it rains and when it rains."

Less sea ice also exposes darker water, which absorbs more energy from the sun. That, in turn, melts even more ice.

2007 broke the record for the lowest extent of sea ice, and 2008 came in second. The third-lowest year on record is 2005, part of a dramatic downward trend that has lasted three decades and doesn't appear to be slowing.

Going forward, experts say, there may be some cooler years when the sea ice may not melt as much. But the long-term trend toward warmer temperatures makes a recovery unlikely.

"We don't see it turning around," Meier said.

He believes that the Arctic could be ice-free in summertime by around 2030 or 2040, but he says more pessimistic estimates predict that could happen as soon as 2013.

"Five years ago, if you'd gone to a conference of scientists and said, 'by 2013 the Arctic sea ice in summertime is going to be gone,' you might have been laughed out of the room," he said.

"No one is laughing now."