A California wildfire that started on Friday doubled in size over the weekend, killing a firefighter and threatening Yosemite National Park. And it’s not the only blaze burning. It’s looking like 2018 could be another big year for wildfires in the United States: 3,362,431 acres have already burned to date in 2018 — an area a little smaller than the state of Connecticut. That’s 4 percent more than the 10-year average for this time of year, despite the fact that the actual number of fires is about 6.7 percent less than the 10-year average.

That dichotomy — fewer fires, more land ablaze — is in keeping with long-standing trends. Since 1985, the trend in the number of wildfires hasn’t changed much, but the trend for total acreage burned has gone up and up and up. So what gives? Experts say there’s no single cause in the midst of all that smoke. Instead, the trend is probably related to the interaction of changing climate, short-term weather patterns and a philosophical shift in how we manage both forests and fires.

Weather cycles and climate changes both play a big role in shaping wildfires, said Carrie Bilbao, a public affairs specialist for the National Interagency Fire Center, the federal agency that coordinates predictive services and wildfire response throughout the United States. For instance, she said, 2017 had a late, wet spring followed by a dry, hot summer. The result was an abundance of vegetation growth that then dried out and turned to kindling. And while weather patterns like that bounce around from year to year, climate changes are also probably affecting long-term trends — with hotter weather, longer growing seasons and even stronger winds that help feed the flames.

And that increasingly fire-friendly climate is coinciding with a time when forests have more fuel to burn. Through most of the 20th century, U.S. forests were managed in such a way as to eliminate as many fires as possible — even though fire was a natural part of forest ecology. Over decades, wild lands built up surpluses of tinder — more trees, more plants, more leaves and twigs littering the forest floor. The more fuel, the bigger and hotter the fires that develop are likely to be, said Brandon Collins, a research scientist with the University of California, Berkeley’s Center for Fire Research and Outreach

Fire managers began to change their philosophy and allow some fires to burn in a more natural way in the 1970s, said Bill Gabbert, a former fire management officer and the current managing editor of Wildfire Today. Over the last 15 or 20 years, that’s become more of the norm. In the past, every little fire that started got put out before it burned much land. Today, one fire might be allowed to eat up much more built-up kindling. In addition, Collins told me, managers are now less likely to try to contain those fires to be as small as possible. Instead, there’s more of a wait and see approach, both because of the knowledge that the forests need to burn and because of an increased emphasis on protecting firefighters’ lives. It’s better to let the fire burn more acreage than risk lives unnecessarily.

But transitioning to a more natural sort of fire management isn’t necessarily going to return the forests to a past state of balance with the blaze, Collins warned. Decades of extreme fire prevention have altered forest adaptation. Areas that burn severely today might never grow back the same way. “You can’t just turn the switch back on,” he said. “We might be turning [some forests] into shrublands.”