Last week, smoke from the fires covered the entire U.S. West Coast before spreading west out over the Pacific Ocean. This week the smoke has travelled thousands of miles east, turning skies from New York to Washington D.C. hazy and reaching as far as the skies above Britain.
In the animation above, Reuters visualises organic carbon released into the atmosphere during the fires. The smoke contains a substantial portion of fine particulate matter known by the particles’ size as PM2.5, which can have a major impact on people’s health.
Smoke can hurt the eyes, irritate respiratory systems, and worsen chronic heart and lung diseases, according to the Centers for Disease Control and Prevention (CDC). It can make healthy people sick if there is enough in the air.
Smoke traveling with air currents high in the atmosphere, however, is unlikely to alter air quality on the ground in faraway places, said Santiago Gassó, an atmospheric scientist at the University of Maryland who works on contract for NASA.
But that does not mean high-altitude smoke has no impact. Wildfire smoke, made up largely of dark carbon particles, can block some sunshine from reaching the ground. And that solar dimming can affect ground temperatures as well as how much energy plants can convert through photosynthesis, or how certain animals might behave, Gassó told Reuters.
“If these smoke layers stayed up there for a month, you would see changes in temperatures, weather patterns, just because you’re putting something up there that doesn’t belong there. You’re changing the dynamics of the atmosphere,” Gassó said.
High-altitude smoke may also have a heating impact. Being dark, carbon particles absorb solar radiation, effectively warming a thin layer in the atmosphere. The net effect on Earth’s climate of these two processes – solar dimming and particle heating – is still a matter of scientific debate.
At ground level
The wildfires – burning across a record total of some 4.8 million acres (1.9 million hectares) as of Thursday – have destroyed towns in Oregon while also devouring forests in California, Washington and Idaho. The ground-level blanket of ash and smoke has made the region’s air quality among the worst in the world.
“Air quality this poor causes health issues for everyone, not just those with existing respiratory conditions,” said Ryan Stauffer, a research scientist at NASA’s Goddard Space Flight Center.
He described pollution levels across the region, and as far as British Columbia, Canada, as “unprecedented.” “Parts of California, Oregon and Washington state have recorded hazardous air quality for over a week straight,” Stauffer said.
Reaching new heights
Smoke from the fires has also pushed the limits vertically, reaching altitudes previously unseen, according to NASA. When extreme fires generate enough heat, it is propelled into the atmosphere creating thunderstorms.
With more fuel to burn, fires also can become hot and energetic enough for the smoke cloud to punch through the natural atmospheric layers above if conditions are right.
That happened on Sept. 7, when huge storm clouds – known as pyrocumulonimbus – rose to a height of more than 15 kilometers, pushing into the stratosphere, as illustrated by data from NASA’s CALIPSO satellite.
The CALIPSO satellite sends laser pulses to measure light scattered back to it from particles in the atmosphere. The data shows a cross section of the atmosphere and distinguishes what the particles are, such as aerosol smoke, clouds, or ice particles.
“The fact that it punched through that layer is very unusual,” Gassó said. “That’s what volcanoes do.”
In the stratosphere, where the ozone layer resides, wildfire smoke particles can spread globally and can take several years, rather than months, to dissipate. Inject enough particles into that layer, and you could be blocking sunshine for a longer time period.
“Whether those particulates would lead to net warming or cooling is a bit of an open question,” Gassó said. “The only experience we have so far has been with volcanoes.” And the evidence from volcanoes is only so helpful, because unlike wildfires, volcanoes send up particles that also reflect and scatter light, rather than absorb it.
The fires across much of Australia in 2019 and 2020 also reached stratospheric levels, NASA reported in January. And smoke from fires in British Columbia in 2017 broke through, too.
“When you have these events so frequently, you start to get concerned,” Gassó said.
Another pyrocumulonimbus cloud was spotted in satellite imagery on Sept. 9, towering above fires around California’s Mendocino National Forest, though to what height is unclear. Those data are not available.
Another tall plume of smoke, possibly a pyrocumulonimbus cloud, was also captured in satellite imagery on Sept. 9. This one was east of San Francisco, further south than the one above.
The fire-induced clouds essentially create their own weather systems. The clouds form from the smoke plume, as the fire’s intense heat warms the surrounding air, causing it to rise rapidly, drawing in cooler air.
The smoke cloud cools as it climbs into the chilly upper atmosphere, colliding with ice particles and building up electrical charge, which can sometimes be released as lightning.
The warm updrafts can pull in so much air lower down that strong winds develop at the ground level, fanning the fire even further so it burns hotter and spreads farther. On rare occasions, these strong and sometimes erratic surface winds can swirl into a dangerous fire tornado.
A fire tornado tore through neighborhoods in Redding, California, during the 2018 Carr Fire. In January this year, an Australian firefighter in New South Wales was killed when a fire tornado flipped over the fire truck he was in.
During this year’s West Coast wildfires, images shared on social media show a tornado funnel appearing on Aug. 16 in a thick plume of smoke from the Loyalton Fire in Lassen County, California.
The challenge for science
Scientists’ understanding of these high-energy fire clouds and how they behave is still an area of active research, now being aided by satellites and other new technologies.
“What’s fascinating about these events is that we’re getting a prime-time view of everything from space,” Gassó said. “We have so many excellent satellite systems right now, and actually this is just the beginning. It’s going to get better.”
In fact, with so much new data pouring in, the challenge is now finding enough researchers to work on analyzing, debating and coming up with new ideas to understand it. For example, what are the physical and chemical results of these smoke particles getting into the stratosphere, where moisture and temperature conditions are very different than in the lower, warmer troposphere?
Studying such effects would likely require duplicating the conditions in laboratory experiments.
With climate change expected to exacerbate fires in the future, by worsening droughts and warming surface ocean temperatures, wildfire research is becoming especially important. Over the last year, the world has seen record fires in Australia, Brazil, Argentina, Siberia and now the U.S. West.
“I’m concerned that we are starting to see these phenomena more often … everywhere in the world,” Gassó said. “If it’s one year like this, it’s fine, as long as it doesn’t keep repeating itself like this.”