In 2010, as Michael Kodas was moving into a cabin on the forested edge of Boulder, Colorado, the Fourmile Canyon Fire ignited in the mountains overlooking the city, destroying 169 homes. It was the first of four fires in four years that would break the “most destructive wildfire” record in Colorado. Five years later the Valley Fire would burn down his brother’s home in California. During the ensuing half decade megafires exploded not only in Colorado and California, but across the United States and around the world. Kodas reported from the scenes of many of them — the Mount Carmel Fire in Israel that killed 44 people including an Israeli police commissioner, the police chief of Haifa, 36 prison guards and a 16-year-old volunteer firefighter; the Black Saturday bushfires in Australia that killed 173 people with fires that carried the explosive force of 1,500 of the atomic bombs dropped on Hiroshima during a heatwave in which Victoria recorded the highest temperatures in 150 years; the 2015 Indonesian wildfires that grew out of blazes set to clear land for agriculture and grew into fires so vast that for 40 days they released more greenhouse gases than the entire U.S. economy.

But after visiting the scenes of some of the most massive and destructive wildfires around the world, Kodas learned that a fire doesn’t have to be huge, hot, or fast to be “mega.” Within 24 hours of his return to the United States 19 of the 20 members of the Granite Mountain Hotshots, one of the nation’s most elite wildland firefighting crews, perished in the flames of the Yarnell Hill Fire, a small blaze burning in the Weaver Mountains of Arizona. He came to realize that megafires were better measured by their impacts than their size, speed, or intensity.

From a family of volunteer firefighters on the Colorado plains facing a grassfire like none had ever seen, to firefighters in a large municipal fire department facing a wildfire that burned down hundreds of homes in their city, to the tragedy of the Granite Mountain Hotshots — a crew that was formed to protect one of the most fire-threatened cities in America and was destroyed in greatest loss of life among professional wildland firefighters in the nation’s history, Kodas constructs a narrative of megafires large and small, and of firefighting disasters both infamous and unknown. Along the way he spends time with dozens of scientists, land managers and firefighters to learn what has changed the behavior of wildfires around the world and what can be done to slow their destruction.

With dramatic storytelling and detailed science, Megafire is both a compelling tale of the disasters the planet’s forested landscapes have already faced and an urgent warning of what’s to come.