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At the Rocky Mountain Research Station’s Fire Sciences Lab in Missoula, Montana, chemists, physicists, fire behavior analysts, ecologists, life scientists, and engineers gather in a cavernous combustion chamber, playing with fire. Stands of metal are draped with what looks like wooden tinsel, made from shredded aspens. The four-foot-high “trees” stick out of an adjustable platform that’s four feet wide and 24 feet long, and can be tilted to mimic a section of the 25-degree south-facing slope of a ponderosa pine forest or the steeper high-alpine terrain of a spruce–fir forest. A huge exhaust hood with smoke sensors hovers over the pad. The acrid taste of decades of smoke permeates the room like a constant reminder of fire’s enduring impact.

Situated around the room, heat sensors and infrared and video cameras await ignition of the “forest.” Researchers hover behind instruments and laptops, their monitors shielded with the same silver material that firefighters use for protection. In an adjacent room, engineers dial in the prescribed temperature and humidity, preparing the combustion chamber for a really good mock conflagration.

Then, with the help of a little alcohol and a spark, the fire begins. Senior scientist and fire behavior expert Jack Cohen practically glows with pleasure as the shredded wood burns, licking the “trees” and climbing up the slope. This particular experiment is designed to give the team a better handle on how crown fires—the big, tree-to-tree events that make for such spectacular TV—spread. The multibillion-dollar national wildfire debate is only becoming more complicated, and the stakes higher.

During the past two decades record-setting blazes have occurred around the world, from Russia to Indonesia, Alaska to Brazil. These “megafires” exceed all efforts to control them, says Jerry Williams, who retired as the U.S. Forest Service’s top fire manager in 2005 and is now a Missoula-based fire adviser. Some of the blazes burn through more than a million acres. Embers launched from crown fire flames can reach two and a half times as high as the burning tree, starting fires up to two miles ahead of the fire front. Flaming debris can strike planes, grounding tanker pilots.

U.S. policy has pitted a deeply ingrained institutional belief that some wildfires can and should be “fought” against a scientific consensus that they are ecologically indispensable. Global warming has kindled the debate further because it has created both hotter and drier conditions in many places. In addition, a legacy of all-too-successful suppression means that many forests now contain huge “fuel stores” of woody debris that periodic fires used to eliminate. Add the fact that droves of people have moved into fire-prone areas, and you have an increasingly combustible mix of policy and ecology. “Megafires are signaling a new era in fire and land-use management,” says Williams.

As the biggest intensify and cannot be controlled by any amount of firefighting, they will surely challenge every conception we’ve had in our ageless history with fire.

In the fall of 1987 Williams was in Happy Camp, California, working a lightning fire spreading through coastal Douglas fir forest, which is a wetter forest that doesn’t typically burn big. As a Forest Service branch director, he kept receiving updates about several fire complexes from northern California to southern Oregon that were growing—and fast. Williams watched the situation reports, dumbstruck by the scale. “This is the biggest thing we’ve ever seen,” he recalls saying about fires in the Siskiyou and Klamath national forests that came to be known as The Siege of 1987 and burned 640,000 acres. At the time he thought, “We’ll never see anything like this again.”

Boy, was he wrong. The following year the Yellowstone fire consumed nearly 1.5 million acres and the national news for weeks. Since then many U.S. states have recorded their biggest fires ever. The term megafire started to attract attention. Experts wondered if “fighting” these colossal fires wasn’t about as effective as dropping DC-10 tanker loads of $100 bills into the flames. More than three million acres have burned each year since 1999—and a 10-million-acre year is almost certainly on the horizon. As the cost of firefighting crossed the billion-dollar mark every year since 2002, another measure of “mega” began to catch policy makers’ eyes: mega expensive. The money being thrown around to douse these fires has pretty much gone up in smoke—and more than 400 wildfire fighters have died since 1987.

Ironically, one of the main reasons we have such a perfect firestorm today is that we’ve been so good at suppressing fires over the past century. There are 10,000 or so U.S. wildlands fires every year, and firefighters put about 95 percent of them out early on. With manpower and a lucky turn of the weather, more are contained. But for about two percent of wildfires, no amount of retardant, fire lines, or Hotshots wielding Pulaskis have appreciable effect. Most firefighting money goes to this minority of massive fires. In 2008 the federal bill hit nearly $1.5 billion, forcing the Forest Service to cut back on other programs.

The physics create nature’s own special effects studio. A smoke plume can form a pyrocumulus cloud. Sometimes the plume rises to the troposphere/stratosphere boundary, at between 25,000 and 40,000 feet, where cooler temperatures stop it. That creates heavier, wetter air that may descend again and create a windstorm and microbursts as it returns to earth, literally fanning the flames. Megafires can also create “fire whirls,” mini tornadoes of spinning flame that can peel off and set their own course, ripping 16-inch limbs off of oaks and generating winds of more than 80 mph. Says Wayne Cook, who has more than 30 years of firefighting experience, “The bottom line is, once you get to that scale, there is nothing you can do to put the thing out until the weather changes.”

The Rocky Mountain Climate Organization reports that from 2003 to 2007, the 11 western states warmed an average of 1.7 degrees Fahrenheit, or 70 percent more than the global average. Many forecasters believe that in coming decades, the West will continue to experience later winters, less snowfall, earlier spring runoff, and generally drier conditions.

As a result, conditions are solidly in place for a political and pyrotechnical firestorm in many forested areas. The western fire season is now 205 days, 78 days longer than in 1986. What’s more, there have been four times as many fires that wiped out more than 1,000 acres than there were in the 1970–1986 period, and six times as much acreage has burned, according to an influential article in Science in 2006 by Anthony Westerling, a researcher at the University of California-Merced. Westerling demonstrated a strong link between climate change and increased wildfires.

One of the most visible effects of warming is the bark beetle infestation that has killed billions of conifers across millions of acres. Deep-freeze winters that once killed off the beetles are mostly a thing of the past. Just how much fire danger these dead forests pose is the subject of scientific debate—and some intriguing hypotheses. On the face of it, scattering the forests with kindling would appear to raise the fire risk. But in an analysis of multiple studies, University of Wisconsin zoologist Martin Simard found that it’s not so simple. In the first year or two after beetles destroy a forest, fire probability does, indeed, increase. But as the needles fall from the trees, the likelihood of crown fires (those that jump from tree to tree, like the ones in the Fire Lab) actually decreases. Years or even decades later, the analysis says, “when beetle-killed snags fall on the ground and understory tree growth creates ladder fuels, the risk of crown fire may again be increased.”

Experts have learned that fire, like top predators, can’t be removed without affecting the balance of an ecosystem. Historically, low-intensity fires periodically swept the landscape, leaving clearings that nurtured fire-tolerant species and helping create a healthy distribution of grasses, shrubs, and trees that sustained biologically diverse regions. The long-standing policy to “fight” fires has been ecologically counterproductive in many places, even though it has saved lives and property. Suppression in the Smokey the Bear era from the 1940s to the 1970s produced many unintended consequences, like a massive accumulation of dead fuel and live biomass. More single-species, same-aged forests led, in part, to unmanageable fires.

The increasing number and size of megafires is triggering changes in regional ecology—for better and for worse. Some burn so hot over larger areas that they virtually sterilize soils and unhinge energy, water, and carbon cycles. Smoke billowing from blazes alters atmospheric chemistry, causing ozone alerts thousands of miles away. In addition, burning forests release vast quantities of greenhouse gases, notably carbon dioxide. Some fish populations have crashed after big fires, and other established species lose their competitive advantages and virtually disappear.

Yet many species not only survive big fires, they thrive because of them. Richard Hutto, director of the University of Montana Avian Science Center, says fires “are one of nature’s best-kept secrets” as a driver of greater biodiversity. The mountain bluebird, for instance, belongs to a category of “pouncers” that exploit the insect explosion in a newly burned forest. Black-backed woodpeckers are so enamored of burned areas that they exist virtually nowhere else, Hutto says. Northern hawk owls in Canada flock to fire-swept places, and in other forests, deer mice populations soar, opening the door for more raptors to move in. Morel mushrooms, those expensive delicacies, proliferate in burned areas. The huge 1988 Canyon Creek Fire in Montana’s Bob Marshall Wilderness may have saved the Big Nell’s geranium, which was thought to be extinct but actually required a good fire to bloom again. That blaze also caused an elk boom because the regenerating landscape “put a lot of new groceries out there,” says Williams.

Ecologists know that changing conditions will benefit some species and harm others. Hutto agrees that trends seem to be pointing toward more, and bigger, fires but worries that policy makers don’t understand that the rewards may be enormous—even from big fires. The pressure to “salvage log” on public lands after a fire is misguided, he says, because “that’s where the real ecological magic begins.”

The question of what to do about megafires is a hot topic. The Fire Lab’s Jack Cohen believes fervently that fires are inevitable and ecologically important, and that we should set more of them on purpose under the right conditions to lower the risk of uncontrollable future fires.

Mark A. Finney, a research forester at the lab, illustrates what that means in practice. In his office, he points to a poster-sized satellite image on the wall, titled “Rodeo-Chediski Fire: June 21, 2002.” The infamous Arizona conflagration devoured 468,000 acres, and this photo shows the charred landscape stretching across many miles, with a few curious green patches. “The only places that are green,” Finney says, circling the sections with a laser pointer beam, “are places where there had been prescribed burns.”

Experts have also found ways to significantly cut property losses. An estimated eight million homes have been built in western U.S. fire zones since 1970, and the bulk of efforts go toward protecting homes and communities in fire-prone areas. Yet research at the Fire Lab and elsewhere shows that homes don’t have to be lost just because the forest around them is. If houses are located 100 feet from combustible materials and are built with materials like asphalt roof shingles that resist the spark of flying embers, it’s possible to save the structures even when the fires themselves are irrepressible. When it comes to most of these fires, Cohen says, “we do not have natural disasters; rather we have human disasters during natural disturbances.”

In the wake of a series of massive burns in California, some of Cohen’s findings are working their way into practice. Insurance companies are bumping their rates in fire zones, as they do in earthquake-prone areas. That may deter development, which is critical, says University of Colorado geographer Tania Schoennagel. She cites a study saying that only about 15 percent of the overlap between wild and urban areas has been turned into residential areas. But that total could grow significantly if we don’t curtail it. “Control fire risk?” asks Schoennagel. “Control development in wildlands.”

Some fire professionals advocate a bigger, faster, more efficient response: loading 747s with fire retardant, and dispatching fleets of DC-10s to bear down on spreading fires. Fire managers employ NASA satellites to figure out how fires will behave and spread, and thermal images beamed from space help them decide how to deploy resources. Weather satellites detect cold fronts moving in, which are almost always preceded by winds that can fan flames. Laser imaging helps determine distance and range as well. And advances like a fire-suppressant material made from frozen crystals of water and carbon dioxide bonded together may also prove useful in some cases. Yet despite all these tools, many fire science experts agree that when the biggest fires rage in the wrong conditions, no human force can put them out.

Clearly, enlisting more squadrons of tanker planes to drop ever-increasing amounts of retardant isn’t going to work in the long run. Neither is letting every fire burn unchecked. There’s a growing consensus that our way out of the hot woods will require a nimble approach to managing the landscape.

In addition to prescribed fires, experts increasingly agree that people can take more responsibility for living in flammable areas. Steven Pyne, a fire historian at Arizona State University and a prolific author on the subject, points out that Australia, for example, is “light years beyond us” in teaching communities how to protect their property by creating “defensible space” around homes—clearing trees and brush a certain radius around their structures. Changing laws to eliminate a mortgage tax deduction for second homes or charging developers the full cost of public services (like putting out rural fires) would go a long way. “Knowing that you might be called upon to protect your house should concentrate the mind wonderfully with regard to wood-shingle roofing, house-clinging shrubs, and firewood stacked under decks,” says Pyne.

Ultimately, though, fire will do what it does, and humans will argue about how to respond. Cohen understands that when it comes to fire policy, philosophy plays as big a role as thermodynamics. His experiments illuminate physical properties of fire in a biological system, but it is in the realm of culture that the debate must play out. “The societal response to fire is about perceptions of personal and property protection,” he says. “The scientific findings are about abstract ecological function and fire physics.”

There’s nothing abstract about a fire burning for weeks or months, choking the sky with smoke and subjecting wildlife, plants, and people to one of nature’s most awesome forces. In the end, “the phenomenon of megafires can be attributed to one common cause—us,” says Pyne. “Even global warming is apparently an outcome of our combustion habits.” Fires, and big ones, are thus part of our flammable planet’s very nature.