In her new documentary, Lucy Walker looks at California’s apocalyptic fires and finds more than the usual smoke and politics.A few times a year, I pull out our HEPA filter and begin reassuring worried friends and family members that, no, the city of Los Angeles, where I live, isn’t burning — or at least not yet. The air quality here is almost always poor, of course, but I tend to switch on the air filter only when the smoke comes, filling the basin and darkening the sky.“The city burning is Los Angeles’s deepest image of itself,” Joan Didion wrote in 1967. It was two years after the Watts uprising, but Didion wasn’t writing about race and reckoning, she was creating a poetically apocalyptic image of the city and, by extension, California. Decades later, she returned to the topic, using a phrase — “fire season” — that now feels obsolete. In the age of enduring drought and climate change, the wildfires never seem to go out in the West, where so many burned in July that the smoke reached the East Coast.In “Bring Your Own Brigade,” the director Lucy Walker doesn’t simply look at the fires; she investigates and tries to understand them. It’s a tough, smart, impressive movie, and one of its virtues is that Walker, a British transplant to Los Angeles, doesn’t seem to have figured it all out before she started shooting. She comes across as open, curious and rightly concerned, but her approach — the way she looks and listens, and how she shapes the material — gives the movie the quality of discovery. (She’s also pleasantly free of the boosterism or the smug hostility that characterizes so much coverage of California.)Specific and universal, harrowing and hopeful, “Bring Your Own Brigade” opens on a world in flames. It’s the present day and everywhere — in Australia, Greece, the United States — fires are burning. Ignited by lightning strikes, downed power lines and a long, catastrophic history of human error, fire is swallowing acres by the mile, destroying homes and neighborhoods, and killing every living thing in its path. It’s terrifying and, if you can make it past the movie’s heartbreaking early images, most notably of a piteously singed and whimpering koala, you soon understand that your terror is justified.To tell the story of this global conflagration, Walker has narrowed in on California, turning her sights on a pair of megafires that began burning at opposite ends of the state on Nov. 8, 2018. (There was also a mass shooting that same day.) One started in Malibu, the popular if modestly populated (about 12,000 people) beach city that snakes along 21 miles of the state’s southern coastline and runs adjacent to a major highway; the other, deadlier fire ignited near Paradise, a town in a lushly, alarmingly forested pocket of Northern California and which, at the time, had more than double Malibu’s population.The contrasts between the areas prove instructive, as do their similarities. As Walker explains, Paradise is tucked into a Republican-leaning part of the state (though its county went for Joe Biden), while Malibu sits in reliably blue Los Angeles County. In 2019, the median property value in Paradise was $223,400 (per the website Data USA); in Malibu, it was $2 million, the city’s Gidget-era surf shacks supplanted by mansions ringed with imported palm trees and incongruously bright green lawns. But, as Walker finds, despite their demographic differences, each area has a history of going up in flames.Drawing on both archival and original footage — including some extremely distressing cellphone imagery and 911 calls — Walker is on the ground soon after the infernos erupt, riding shotgun with a fire battalion chief in Southern California and interviewing residents who managed to get out of Paradise alive. She jumps around in time a bit, shifting forward and back as she surveys the terrain, fills in the backdrop and introduces a range of survivors, heroes, scientists and activists. She seeks answers and keeps seeking, building on regional contrasts to create a larger global picture. (Three cinematographers shot the movie and three editors seamlessly pieced it together.)The story Walker tells is deeply troubling and often infuriating, and stretches back past 1542, the year that the Iberian explorer Juan Rodríguez Cabrillo dropped anchor in an inlet now known as the Los Angeles harbor region. He named the area La Bahia de las Fumas, or the Bay of Smokes. For thousands of years, native peoples up and down the West Coast had built campfires, but also used fire to productively manage the land. In the centuries since, fire management has come to mean fire suppression at any cost. The problem is, as Walker methodically details, fire suppression isn’t working: The top six largest California wildfires in the past 89 years have all happened since 2018.That’s bleak, but I’m grateful to Walker for not leaving me feeling entirely hopeless about the future of my home and — because this movie is fundamentally about our planet — yours as well. Climate change is here, there’s no question. But, she argues, we can do much more than curl up in a fetal position. The problem, as always, is people. And when, a year after Paradise burned, residents in a meeting complain about proposed fire codes that may well save their lives in the next conflagration, you may shake your head, aghast. Human beings have a disastrous habit of ignoring our past, but Lucy Walker wants us to know that there’s no ignoring the fires already destroying our future.Bring Your Own BrigadeRated R for upsetting images and audio of people trapped by fire. Running time: 2 hours 7 minutes. In theaters. More