(CBS) Professor Swetnam wanted to show 60 Minutes just how much has changed, so he brought Pelley to the top of Arizona's Mount Lemon. Two mega-fires there killed everything, even the Ponderosa Pines.

"You know, I was always taught that Ponderosas were big, robust trees that were built to withstand fire," Pelley remarks. "And that when everything else burned off, the Ponderosas were still standing. But look at them."

"The Ponderosas are able to withstand the low severity fires where you get flames of maybe one to two or three feet high. But now the behavior of these fires is off the scale," Swetnam says.

Asked how much things have changed, Swetnam tells Pelley, "Well, we're seeing century-old forests that had never sustained these kinds of fires before, being razed to the ground."

Back at the battle to save Ketchum, Idaho, the day shift was coming off, and the night shift going on.

How long does it take to bring a fire like this under control?

Says Tom Boatner, "This particular fire is about 45,000 acres and they’ve been working on it for about 11 or 12 days and they've got it about 50 percent contained and with any luck they will finish containing this fire in another five or six days something like that."

Containing it meant fighting fire with fire. Using drip torches, they started a controlled burn around the town, creating a barrier, so that when the forest fire hit there'd be nothing left to burn. These pre-burns are risky though. Trees can torch suddenly and explosively, sending embers up to a mile away.

By daybreak on the 18th day, the gamble had paid off. The blaze came within 100 feet of some homes, but not one home was lost. It will take years for this forest to recover, but Tom Swetnam told Pelley with these new super hot fires some forests may never grow back.

"We used to have forest soil here that might have been this deep," he says, indicating about a foot of depth, "but now we're just down to rock."

"So you're down to mineral and sort of a rock, sort of armored soil. And that is not a good habitat for trees to re-establish," Swetnam says.

"Where do you think all this is headed?" Pelley asks,

"As fires continue to burn, these mega-fires continue to burn, we may see ultimately a majority, maybe more than half of the forest land converting to other forest, other types of ecosystems," Swetnam says.

"Wait a minute. Did you just say that there's a reasonable chance we could lose half of the forests in the West?" Pelley asks.

"Yes, within some decades to a century, as warming continues, and we continue to get large scale fires," Swetnam replies.

Swetnam says that this is what we have to look forward to. He estimates, in the Southwest alone, nearly two million acres of forest are gone and won't come back for centuries. The hotshots are already planning for the next fire season. In 2006, the feds spent $2 billion on fire fighting, seven times more than just ten years ago.

"You know, there are a lot of people who don't believe in climate change," Pelley remarks.

"You won't find them on the fire line in the American West anymore," Tom Boatner says. "'Cause we've had climate change beat into us over the last ten or fifteen years. We know what we’re seeing, and we're dealing with a period of climate, in terms of temperature and humidity and drought that's different than anything people have seen in our lifetimes."

Produced By David Gelber and Joel Bach
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