 Every year you can count on forest fires in the west, like hurricanes in the east. But recently there has been an enormous change in western fires. In truth, we've never seen anything like them in recorded history. It appears that we're living in a new age of mega fires, forest infernos ten times bigger than the fires we're used to seeing. To find out why this is happening, we went out on the fire line to see the burning of the American West. Last fire season was the worst in recorded history. This year is already a close second with two months to go. More than 8 million acres have burned this year already. These are the men and women facing the flames. Elite federal firefighters called hotshots. Nationwide there are 92 hotshot crews of 20 members each. We found these New Mexico hotshots in the Salmon River Mountains of Idaho. They'd set up a camp in a burned out patch of forest with fire raging all around. They were hitting the day exhausted, half way through a 14-day shift. If you guys want to go down and evaluate. I'll take myself and a couple scouts and we'll go down there and take a look. I'm anticipating a mess today. Oh yeah. Sucks, yeah. They found the mess they expected. The valley was engulfed in smoke. The flames blew through the fire brake lines they dug the day before. We were trying to turn the corner yesterday and that's when it kind of blew out. And I think we got more ground over here that's been taken. So, any questions? No question this day the fire won. It surged across the mountain forcing the hotshots to evacuate. All across the west crews are playing defense, often pulling back to let acres burn, but standing firm to save communities. Last and this season came in August at Ketchum, Idaho. Forecasters said it was 99% certain that Ketchum would be lost if nothing was done. Fire crews came from across the nation, local, state, federal, 1,700, working round the clock from a mountain side camp. Remember that as the winds come through, fire wants to move up hill, down hill, wherever the thunderstorm's pushing. It's gonna move. Two foot flames headed for these homes, residents evacuating. Within the next six hours. We joined up with Tom Boatner, who after 30 years on the fire line, is now the chief of fire operations for the federal government. A fire of this size and this intensity in this country would have been extremely rare 15, 20 years ago. They're commonplace these days. 10 years ago a big fire was what? 10 years ago, if you had 100,000 acre fire, you were talking about a huge fire. And if we had one or two of those a year, that was probably unusual. Now we talk about 200,000 acre fires like it's just another day at the office. It's been a huge change. And the biggest fires are what now? We've had, I believe, two fires this summer that have been over 500,000 acres, and one of those was over 600,000 acres. You wouldn't have expected to see this how recently? We got records going back to 1960 of the acres burned in America. So that's 47 fire seasons. Seven of the 10 busiest fire seasons have been since 1999. You know what? It's hotter than hell right here. It's getting pretty damn hot. It is up. So you can imagine the challenge for young men and women with hand tools like this to come up here and try to put out a fire like this. But there's thousands of people down there with multimillion dollar homes that are counting on them to do that. And doing that safely is our big challenge. We'll drop down the hill here. It was 20 years ago that firefighters got their first glimpse of what was to come. This is Yellowstone in 1988 when a third of the National Park burned. Since then, fires have broken records in nine states. Several megafires like this one in Arizona have burned over half a million acres each. Why are there more of these fires? It turns out that the Forest Service is partly to blame with a policy that it started 100 years ago. The Forest Firefighter Service stops fires. Forests, brush and grass fires. The policy was to try to put out all fires immediately. Because we so successfully fought fire and eliminated fire from this ecosystem for 100 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 have seen in a forest like this. Is it possible that we're going to get to the point where we have these megafires and we just can't fight them? Because they're too large? 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. 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. Here, this is the Giant Sequoia collection. At the University of Arizona, Swetnam keeps a remarkable wood pile. This is the largest collection of tree rings in the world. His rings go back 9,000 years and each tree ring captures one year of climate history. And if I'm reading this right, this ring right here is the birth of Christ. That's correct. Swetnam found that recent decades have been the hottest in a thousand 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. 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. The spring comes earlier, so the fire season is just longer. 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 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 that Tom Boatner has noticed for about 10 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. And look how easily it's burning. Yeah. Straight up the hill. Even at the end of August at 6,000 feet in the Rocky Mountains, this fire is just cooking right along. Professor Swetnam wanted to show us just how much has changed. So he brought us to the top of Arizona's Mount Limit. Two megafires here killed nearly everything, even the Ponderosa Pines. You know, I was always taught that the Ponderosa's were big, robust trees that were built to withstand the fire and that when everything else burned off, the Ponderosa's were still standing. But look at them. The Ponderosa's 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. How much have things changed? Well, we're seeing century-old forests that had never sustained these kinds of fires before being raised to the ground. Back at the battle to save Ketchum, Idaho, the day shift was coming off. Night shift going on. How long does it take to bring a fire like this under control? Well, this fire right now, this particular fire's about 45,000 acres and they've been working on it for about 11 or 12 days. And they've got it about 50% contained and with any luck they'll finish maintaining this fire in another four, five, six days. 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 preburns are risky though. Trees can torch suddenly and explosively like these. 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 Sweatnam told us that with these new super hot fires some forests may never grow back. I used to have forest soil here that might have been this deep, but now we're just down to rocks. You're just down to the rocks here. So you're done to mineral soil and that is not a good habitat for trees to re-establish. Where do you think all this is headed? 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 types of ecosystems. Wait a minute, did you just say that there's a reasonable chance we could lose half of the forest in the west? Yes, within some decades to a century as warming continues to get large-scale fires. Sweatnam says that this is what we have to look forward to. He estimates that in the southwest alone nearly two million acres of forests are gone and won't come back for centuries. The hot shots are already planning for the next fire season. In 2006, the Fed spent $2 billion on firefighting seven times more than just 10 years ago. You know, there are a lot of people who don't believe in climate change. You won't find them on the fire line in the American west anymore because we've had climate change beat into us over the last 10 or 15 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.