Photo by Donny O’Neill
Neil Lareau says he hasn’t seen any precipitation in the Sierra Nevada, where he lives, since he went skiing on Cinco de Mayo. It’s July now, with a series of heatwaves billowing across the West and Dr. Neil Lareau, an atmospheric scientist and member of the POW Science Alliance who studies extreme wildfires, says that the spiking temperatures and lack of moisture are stacking the deck for another big wildfire fire season.
We’ve always had wildfires, and fire is an intrinsic, good part of the earth’s system. We need some level of fire to regenerate ecosystems. But fire is also one of the most complex physical systems we have. It responds to fuels and weather and chemistry and human dynamics and these days it’s responding to a thirsty, warming climate.
The last few summers have been some of the hottest on record, with 2023 topping the list, and Lareau says that a hotter summer is also a drier summer, especially in the west. Hot air holds more water, so when it’s hot the atmosphere is thirstier. To quench its thirst, it sucks up moisture from the landscape, drying out grass and trees, desiccating the land and turning the dry vegetation into fuel for wildfires.
With summers setting heat records year over year, fuel for wildfires become more abundant. When vegetation is wet, it’s hard to ignite—as anyone who’s ever tried to light a soggy campfire can attest—but when it’s dry and abundant it burns hot and fast, manifesting in higher intensity fires.
Lareau says that fuel is our clearest signal of how climate change is creating more fire hazards. It’s the way our longer hotter summers build a house of cards for fire risk and then a trigger—like heat domes, lightning strikes or human ignition—knocks it down.
“That’s the difference between climate and weather,” he says. “Climate is the set-up, weather is the knockdown.”
Even in a world with hot, long summers, which are full of fuel, we’re getting a range of different fire types. Healthy fires come through at lower heat and lower flame length burning some of the ground level surface fuels, cleaning up the fuels leaving tree canopies intact. While some amount of high-intensity fire is natural and not necessarily bad for the ecosystem, the area burned at high intensity is going way up—recent research argues for an eightfold increase in the area burned at high intensity.
But when it’s hot and there is abundant fuel on the landscape, fires burn hotter and longer, consuming all the available fuel, and incinerating whole forests and grasslands. Those conditions create the kind of catastrophic fires we’re seeing more frequently: hotter, bigger, more destructive and longer lived.
The summer of 2023 was an example of that. “I still can’t wrap my head around the magnitude of the Canadian wildfire season last year, it was literally four times worse than anything in the satellite record,” Lareau says.
Part of why those fires were so bad is because they burned for so long. Lareau says fire is kind of like a living organism—it grows and spreads—and once there’s fire on the landscape, it leads to more fire. “Lengthening fire season is problematic in that way,” he says. “The earlier a fire gets established the more days it has to work with.” For instance, in California in 2021, the Dixie Fire started in July and burned through the end of October, torching a million acres across the Sierra Crest.
Lareau’s research focuses on extreme fire behavior. He tracks huge wildfires to try to understand the way fires make their own weather, like fire tornados, fire generated thunder, and pyrocumulonimbus clouds that happen within humongous storms. We’ve always had extreme fire behavior,” he says. “But now it’s kind of like we’re rolling the dice more.” Extreme heat and abundant fuel creates more extreme fires, which can then create their own weather, like high winds that drive the fire bigger and hotter. He says we know that those kinds of fires are driven by climate change, as opposed to fire management techniques or land use policy because they’re happening all over the globe.
He says that some of our biggest recent fires, like the East Troublesome Fire in Colorado’s Rocky Mountain National Park, the Camp and Dixie Fires in California and the massive glut of a fire (Beachie Creek Fire, Archie Fire and more) on Labor Day 2020 that devastated parts of Oregon were driven by those dynamics. Those mega fires become particularly destructive when run into developed areas. “Houses are super dry and full of material. Once the homes become the fuel you can’t do much at that point besides get people out of the way,” he says.
Aside from the destruction of homes and forests—and sometimes the tragic loss of life—there are broad public health consequences from the fires, and they have a wider reach when the fires are bigger and burn for longer. If you live somewhere that has frequent fires, you’re probably used to tracking air quality due to smoke, but as those fires grow, the impacts spread.
“The number of people who are impacted by the amount of smoke vastly outnumbers the people directly impacted by the fire,” Lareau says. “Last year the smoke was impacting people in New York and Boston. It was a wake up for people who don’t have it as part of their daily lives in the summer.” That smoke has a cascade of negative health impacts from stroke and heart failure, to decreased birthweight of infants whose mothers were exposed to smoke.
And then once the smoke clears and the burning stops, we’re left with the ecological and personal impacts of the mega fires, which torch neighborhoods and incinerate ecosystems, changing nutrient availability, water runoff and so much more.
“Landscapes that you’ve internalized and love may not come back,” Lareau says. “There’s an emotional component— I’ve personally felt a sense of loss—and then from a recreation standpoint, when you’re hiking and biking in these places it’s going to be exposed and hot after the fire. It might take a really long time for vegetation to come back.”
The upside is all of this, Lareau says, is that fire is an environmental disaster that we know how to address. “We actually know the solution,” he says. The long term solution is cutting back fossil fuels—not continuing to make the atmosphere hotter and drier. And in the shorter term we can reduce the risk of large, destructive wildfires by managing fuels, limiting unnecessary ignitions, and building resilience into our landscapes, homes and infrastructure.
But just because we know the solutions, doesn’t mean it’s easy. One of the big ways we manage fire risk and mitigate fuel build-up is through controlled burns, but because of rising temperatures, there are fewer days that it’s appropriate and safe to set prescribed fire. “It’s hard to get enough fire on the landscape to manage the problem because there’s not enough days to do it right,” Lareau says. We’re working in a climate constrained environment. But there are other ways we can learn to live with fire, from the personal, like avoiding campfires; to the small scale, like thinning out the trees in your neighborhood; to state and nationwide projects, like hardening infrastructure like powerlines to minimize ignitions. He says that high intensity fires are here to stay, we’re in an era that scientists are calling the Pyrocene, because of how much fire is influencing our lives and now our challenge is to curb our climate impacts and learn to live with fire in a healthier way.
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