Deep Freeze Or Baked Alaska?

As a global warming conference was underway in Kyoto, Japan, last December, CBS News Correspondent Jerry Bowen traveled to Alaska's Bering Glacier and witnessed a dramatic and mysterious meltdown. He filed this report.

Alaska's Bering Glacier, the largest in all of North America, is a vast ice field 140 miles long. It is moonlike on the surface, and mysterious from the air. A massive ice block can suddenly up-end to become a perfect blue pyramid so enormous that a passing plane looks no bigger than a fly.

First Person Report: Click here for a behind-the-scenes look at Ice Station SHEBA.(CBS)
However, the very real mystery here is why the glacier is melting so quickly, in some places retreating as much as half a mile a year.

"Since about the start of the century, it's retreated in places more than 10 miles," says Bruce Molina of the U.S. Geological Survey. "We have predicted that within the next 50 years, the glacier could retreat as much as an additional 30 miles."

Much of Berg Lake drained away when an arm of the Bering Glacier, weakened by decades of melting, suddenly collapsed. The glacier had been acting as a dam. When it blew out, water poured out of this basin for three days, and the level of the lake dropped more than 330 feet.

A massive ice block turned on its end by the glacier.(CBS)
But Molina is reluctant to blame global warming. "As a scientist, global warming is a term that bothers me," he says. "It implies a uniform change over the entire surface of the Earth. I think we're looking at an extremely dramatic example of changing climate. I certainly agree the climate is changing. The real unknown, though, is what is causing this climate change."

The climate change, the warming that's certainly taking place here, is by no means uniform. In fact, 4,000 miles to the east of the Bering Glacier, weather stations in Greenland are reporting that temperatures are actually getting cooler.

Scientists say these variations are to be expected, even with global warming. The question is whether the climate change is part of a natural cycle, or a result of increased solar activity (including a hotter sun) or is manmade (due to the greenhouse effect, which is a warming of the atmosphere because of the burning of fossil fuels).

No one disputes there's been a dramatic change in Alaska, an increase of 5 degrees in average temperatures in just the past 20 years, far faster and hotter than the 1-degree global increase over the last cenury.

In the past two years, the ice edge of the Bering Glacier has receded fully a third of a mile.

Bureau of Land Management biologist John Payne also is tracking the Bering. Payne says the pullback stops roughly every 30 years, when the glacier briefly surges forward in an explosion of icebergs and flooding, and then starts to retreat faster than ever.

"I've never seen something move that rapidly backwards," Payne says. "You wonder sometimes what's going on here."

What's going on is that America's deep freeze is slowly turning into a baked Alaska. And if the scientists are right, it's far from over.

Click above for CBS News Correspondent Jerry Bowen's complete report.

Reported by CBS News Correspondent Jerry Bowen