Climate change makes wildfires in California more explosive

Towering smoke plumes overshadowed California's town of Paradise as the Camp Fire raced through in 2018. More than 18,000 acres burned in a matter of hours. Josh Edelson/AFP via Getty Images hide caption

toggle caption Josh Edelson/AFP via Getty Images

Towering smoke plumes overshadowed California's town of Paradise as the Camp Fire raced through in 2018. More than 18,000 acres burned in a matter of hours.

Josh Edelson/AFP via Getty Images

During some of the worst hours in Camp Fire, which in 2018 burned the town of Paradise, California to the ground, the fire was growing so fast it within just 90 minutes.

Wildfires like the Fire that intensify and spread enormously within a, keep fire experts up at night. Now a , published Wednesday in Nature, uses a machine-learning model to show that climate change has nudged the risk of fast-spreading fires up by about 25% on average in California. That's compared to a time before humans heated up Earth's atmosphere by burning vast amounts of fossil fuels.

that sprang to life from 2003 to 2020, 380 of them included at least one day when they grew by at least 10,000 acres — an area as big as most of Manhattan. Climate change ramped up the likelihood of that growth for most of the fires–but not all of them.

The team found there were critical thresholds governing fire behavior. For fires burning near the thresholds, climate change could tip them into a more dangerous state.

"It's kind of like if you're wondering if growing a couple inches will help you dunk," Brown explains. If you're really tall already, he says, a few extra inches won't make a big difference. But if you're 5' 10", a little boost could get you over the rim. "We see the same thing with wildfires. If you're right on the precipice of these thresholds, then warming causes them to cross over that threshold and increase the risk of danger," he says.

The atmosphere is a thirstier sponge

The thresholds were primarily associated with the , a fancy term for how air pulls water out of dead or live plants and other burnable materials. Hotter air –one of the hallmarks of human-caused climate change–sucks moisture more strongly out of those pieces of potential tinder. has shown that fires can grow much bigger and more intense when they have plenty of dry, crispy fuel to burn, a factor heavily influenced by big vapor pressure deficits.

via strategies like, for example, means there's less fuel to burn. More than are started by people, and those fires burn. Getting that number in check could greatly lessen risks.

To Mortiz, the challenge now is partly about considering climate's influence on wildfire risk while figuring out how to minimize the risks of fire for and communities.

His research group has looked at how human-scale decisions, like neighborhood design or house placement, affects . "We realized the strength of housing densities on fire activity rivals the strength of climate variables in some parts of California," he says. Those choices are well within peoples' ability to control, through zoning policy, or building codes, or . "We have to be more holistic in our understanding of 'risk,' to look at the human side as well," Mortiz says.