The Age Of Mega-Fires

Expert: Warming Climate Fueling Mega-Fires

(CBS)  It was 20 years ago that firefighters got their first glimpse of what was to come. In 1988, a third of Yellowstone National Park burned. Since then, fires have broken records in nine states. Several mega-fires, like one in Arizona, have burned over half a million acres each.

Why are there more of these fires? Turns out the forest service is partly to blame with a policy it started 100 years ago.

The policy was to put out all fires immediately. "Because we so successfully fought fire and eliminated fire from this ecosystem for a hundred years, because we thought that was the right thing to do, we’ve allowed a huge buildup of fuel in these woods. So now, when the fires get going, there’s a lot more to burn than historically you would’ve seen in a forest like this," Boatner explains.

"Is it possible that we're gonna get to the point where we have these mega-fires and we just can't fight them because they're too large?" Pelley asks.

"Well, we're there already. We have identified numerous fires this summer that we know we can't put out with the resources we have available. Because of the severity of the burning conditions and the size of the fires," Boatner explains.

The severity of the burning and size of the fires caught the eye of Tom Swetnam, one of the world's leading fire ecologists. He wanted to know what's touched off this annual inferno and whether it's truly a historic change.

At the University of Arizona, Swetnam keeps a remarkable woodpile, comprised of the largest collection of tree rings in the world. His rings go back 9,000 years, and each one of those rings captures one year of climate history.

Swetnam found recent decades have been the hottest in at least 1,000 years. And recently, he and a team of top climate scientists discovered something else: a dramatic increase in fires high in the mountains, where fires were rare.

"As the spring is arriving earlier because of warming conditions, the snow on these high mountain areas is melting and running off. So the logs and the branches and the tree needles all can dry out more quickly and have a longer time period to be dry. And so there's a longer time period and opportunity for fires to start," Swetnam says

"The spring comes earlier, so the fire season is just longer," Pelley remarks.

"That's right. The fire season in the last 15 years or so has increased more than two months over the whole Western U.S. So actually 78 days of average longer fire season in the last 15 years compared to the previous 15 or 20 years," Swetnam says.

Swetnam says that climate change -- global warming -- has increased temperatures in the West about one degree and that has caused four times more fires. Swetnam and his colleagues published those findings in the journal "Science," and the world’s leading researchers on climate change have endorsed their conclusions.

But what was news to the scientists is something Tom Boatner has noticed for about ten years now. "This kind of low brush would normally be really moist and actually be a fairly good barrier to fire. But as I look at this I just see wilted leaves everywhere. There's no moisture left in them. They're dead," he points out.