Climate scientists expect wildfires to grow in frequency and intensity as the planet warms. Now new research indicates the fires themselves could be accelerating climate change faster than previously thought by spewing huge soot particles into the atmosphere.
That’s worrying because this "super-soot" causes 90 percent more global warming than standard-size particles because the bigger soot traps more heat in the atmosphere, according to a study published recently in the journal Scientific Reports. What’s more, existing climate change models make their calculations using smaller soot particles, meaning scientists may be underestimating the impact of wildfires on global warming.
“It builds a strong case as to why we need to study these particles, because wildfire soot accounts for a total of 35 percent of soot emissions globally,” said Rajan Chakrabarty, the study’s lead author. “In Southeast Asia and Russia, wildfire soot can be up to 65 percent of regional soot mass.”
The study’s conclusions are based on data samples collected from a 2012 wildfire in India’s Nagarhole Forest and wildfires in Northern California, New Mexico, and Mexico City.
The research is the first to identify the existence of the larger particles, dubbed superaggregates. They are 10 times longer than conventional soot particles from car exhaust or cook stoves and have irregular shapes.
Superaggregates are formed during intense wildfires or when high volumes of fossil fuels burn. Soot particles collide and stick together while trapped in vortexes circling within the flames, according to Chakrabarty, a professor affiliated with the Desert Research Institute at the University of Nevada in Reno, as well as Washington University in St. Louis.
These superaggregates trap air inside them that increases their surface and size. “A superaggregate is going to absorb or trap more heat in it rather than reflect or scatter it because its surface is nonhomogeneous, so the atmosphere warms up in its vicinity—like the blanket effect,” Chakrabarty said.
Why haven’t these particles been identified before? “People have seen them but not identified them,” Chakrabarty said. “Sampling a wildfire plume is extremely difficult.”
Not many fire studies have been done, especially during the flaming phase, because the flame front moves so fast that it’s risky to do real-time measurement, he said.
Chakrabarty is working with scientists affiliated with the Intergovernmental Panel on Climate Change to feed his wildfire soot study results into climate change models.
“The next IPCC assessment will be different—our data will improve the estimates,” he said. “The bottom line is, when climate modelers talk about soot, one has to take into consideration the size and the scale of the fire and also what source it is coming from.”