Editor’s Note: This article was originally published in an edition of NOVA’s email newsletter, NOVA Lens, and has now been repurposed for NOVA Next. Sign up for NOVA Lens here (select “NOVA Newsletters”). This week, the death toll of California’s “Camp” and “Woolsey” wildfires rose to at least 66; swift and furious flames in the Northern and Southern regions of the state have destroyed more than 200,000 acres. Camp Fire alone has forced at least 52,000 people to evacuate the town of Paradise and the surrounding Butte County—and more than 600 people are still missing. By this past Sunday night, Camp Fire had become the deadliest single wildfire in California’s history.

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That tragic distinction signifies a new era, according to Crystal A. Kolden, an associate professor in the Forest, Rangeland, and Fire Sciences department in the College of Natural Resources at the University of Idaho. “We now have mass-fatality wildfires—specifically civilian fatalities,” she said, noting that this is a recent trend. Prior to about two years ago, most wildfires in the U.S., except for a few outliers, didn’t kill civilians. And the fires were smaller, too—a fire that burned tens of thousands of acres was considered huge. Now, seething scorchers in the West zip through parched shrubbery at 80 acres per minute, often near what is called the urban-wildland interface: regions close to forests where people make their homes. The fact that most fires in the U.S. have been destructive but not deadly is both a Catch-22 and a sign that a well-intentioned but ill-fated (at least in many regions) strategy called fire suppression has worked… temporarily. Although fewer people died in the past, the United States’ history of putting out fires has permitted additional plant growth—flammable material that we didn’t allow to burn and is now vulnerable to catching fire en masse. That means bad news for fires that occur today, particularly since climate change now figures into the picture—and because little thought was ever put into wildfire death prevention. “For most natural hazards in the U.S., we’ve actually done a really great job reducing fatalities through planning, predicting, developing warning systems, and improving our infrastructure,” Kolden said. “We haven’t done that for wildfires because we haven’t had a lot of fatalities.” Now that wildfires are becoming worse due to a confluence of factors, Kolden says scientists are trying to figure out what the sweet spot is when it comes to controlled (a.k.a. prescribed) burns: intentional manmade wildfires that help reduce the intensity of future fires by limiting the accumulation of flammable fuels. “Prescribed fire is used for two different purposes,” she said. “The first purpose is to reduce the amount of brush and the amount of fuel that’s available for the fire in the understory [beneath the forest canopy]. The other purpose is that it reintroduces fire in places where fire burned frequently historically.”

Scientists know from tree ring records that certain regions experienced wildfires as often as every three to five years; taking out understory brush removed competition for water and nutrients among the bigger trees. Today, these areas are not used to combustion-less living. In other words, the land misses the fire. As much as 20 to 30 million acres a year used to burn prior to the West Coast European settlement period. “If you look at the Lewis and Clark journals, there’s an enormous amount of discussion about how smoky the air is,” Kolden said. This is no longer the case—but perhaps more important is the particular pattern that’s been lost. Frequent fires allowed for a patchwork quilt of landscape ages to materialize, since fires would come up against recently scalded land and stop. Now we have a lot of old brush and a lot of new brush—but not a lot of in-between brush. “That sort of homogeneity in the lack of a patchwork is really problematic for an ecosystem,” Kolden explained. While the expected role of forest management agencies in helping resurrect a foregone period is contentious and misunderstood, Kolden says that one thing they can do is thin out smaller vegetation and underbrush to allow large trees to get bigger and better-spaced again. “Unfortunately, that’s not very profitable,” she noted. “It costs more to do that type of work than they will make for the value for the timber.” Ultimately, the sheer force of these climate-change-buffered fires is wreaking immediate havoc on old, under-prepared communities. And though many modern homes were built under more stringent fire codes, older homes literally become fuel for the flames. “They’re the primary fuel, not the forest itself,” Kolden said. What makes matters worse is that many of the people who live in these old, urban-wetland interface homes were priced out of more expensive urban regions. They can’t afford the necessary fireproof updates to their homes. It’s a vicious cycle that has few escape routes, either locally or globally. In Slate, Stephen Pyne, a professor in the School of Life Sciences at Arizona State University specializing in the history of fire, writes, “We used to think fire history was a subset of climate history; now climate history is becoming a subset of fire history.” Kolden explains that, from a science perspective, this is what’s known as a positive feedback loop: “As we have ignitions from fires going into the atmosphere, it alters the climatic system. As it alters, it promotes [the atmosphere] generally toward warming, which promotes more fire.” At a broader level, what we’re seeing in the changing climate is, according to Pyne, a mere symptom of what he calls the “Pyrocene,” or the era in which humans have fundamentally altered how things burn on Earth. "Our fire history used to be about finding new stuff to burn," Pyne told NOVA. "Now, it’s more about dealing with the effluent of all that burning."

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The Pyrocene didn’t necessarily start when fire suppression began, but the practice was certainly a turning point. “At the end of the 19th and the early part of the 20th century,” before fire suppression methods took hold, Kolden said, “people did die in wildfires—by the thousands.” Fewer people died once fire suppression techniques gained popularity, but now we’re looking at a return to the past because of it. “We are moving back toward that if we don’t change the way we approach wildfires.” Editor's Note: This article was updated on November 17 to include a direct quote from Stephen Pyne.