The Line fire had burned through more than 21,000 acres of Southern California when officials announced Monday morning that it was only 3% contained. Amid record temperatures, the blaze quickly ate through dry vegetation, injuring three firefighters and leading to evacuation orders for more than 6,000 people across San Bernardino County.
It’s just one of 67 large wildfires currently burning across more than 2 million acres of the country. While the end of summer has typically meant a slowdown of major wildfires, climate change has upended that seasonal pattern.
So what’s different about today’s wildfire weather?
‘Whiplash’ Weather Feeds the Fires
The Line fire and others feed on a “whiplash” between very wet conditions and extremely hot conditions.
“It’s arguably the worst climate sequence for the wildfire in Southern California,” said Daniel Swain, a climate scientist at the University of California, Los Angeles. For the past two years, wet conditions have caused vegetative growth that quickly dried out during the coastal heat wave that began last week. Fire intensity and behavior are functions of how much fuel is available to burn, so a rapid loss in moisture can create a feast for wildfires.
The phenomenon is so new, Swain said, science could require a new term to articulate. That’s because climate change makes it increasingly likely there will be back-to-back seasons like these of extreme rain, followed by extreme heat, that could worsen fire conditions.
The Heat Is Hotter Than Ever
A heat wave descended on the West Coast last week. Seven communities in Southern California experienced record heat Sunday.
Excessive-heat warnings remain in effect across the region until Monday night. The temperatures come at the tail end of the hottest summer on record, according to Copernicus, a European Union agency that tracks climate change. The world as a whole also remains well on its way to the hottest year on record.
Nights Don’t Offer Relief
Another danger to record-setting temperatures is they are now less likely to let up at night. Overnight hours typically lower temperatures and increase relative humidity, or how much water vapor is in the air, which together can help limit a fire’s spread.
But climate change has accelerated nighttime warming, and now fires can burn more often overnight, a phenomenon that continued across the country this month, according to the National Interagency Fire Center, making it tougher to contain wildfires.
Fires Spawn Their Own Weather
When wildfires become big and intense enough, they can generate their own weather.
Pyrocumulonimbus clouds are huge, smoke-filled thunderstorms that can create hail, wind, lightning and even tornadoes. Such storms can make a fire extremely difficult to put out.
“It can be this whole apocalyptic scene, which makes it more hazardous,” said David Peterson, a meteorologist at the U.S. Naval Research Laboratory in Monterey, California.
This weekend, five of these anvil-looking clouds formed across Oregon, Wyoming, Idaho and California. A pyrocumulonimbus cloud, or pyroCb to those in the know, grew 40,000 feet tall above the Line fire and caused the fire to rain on itself.
“Yesterday there was a veritable conga line of pyroCbs up in Idaho,” Swain said. The conditions created fire-generated storms 60 miles north of Boise.
Reliable data on these cloud formations goes back only to 2013 but it shows that as the number of extreme wildfires increases, so too do pyroCbs. Between Canada and the Western United States, 82 have formed so far this year, with at least 10 of those happening in the U.S. over the past two weeks, Peterson said.
The Smoke Is a Health Risk
More wildfires mean more smoke. And more extreme fires that burn bigger and hotter, burrowing deeper into the soil, can spread that smoke farther afield. Last summer, Canada’s record wildfires blanketed North America with a haze as far south as Florida.
When people breathe wildfire smoke the tiny particles lodge in their lungs and bloodstream, potentially affecting organs throughout the body. Studies have linked smoke exposure to some cancers, higher risks of heart attacks, childbirth and pregnancy complications, and mental health issues.
Fire Seasons Are Shifting
“Fire season is lengthening and expanding,” said Swain, who wrote that the Western United States this month was heading into a “second season” for wildfires. After a surge in extreme wildfires in July that helped produce the Park fire, California’s fourth-largest to date, Swain said there may be another surge in September and October in some regions.
What Can We Do?
Lowering the risk of wildfires requires better maintenance of flammable matter, which can be controlled by “prescribed” burns, which is the intentional and controlled burning of brush and grasses to minimize the chance they can fuel much larger wildfires.
It also requires limiting greenhouse gas emissions. Climate change is caused by emissions of carbon dioxide and other planet-warming gases into the air, mainly from the burning of fossil fuels.
“We know those are primary contributors to heat-trapping emissions supercharging the dryness of the ecosystems that are part of these fires,” said Carly Phillips, a research scientist with the Union of Concerned Scientists.
