— Scienceline (@scienceline) April 14, 2015
Below are excerpts from an article at Scienceline.org:
“It’s a hot day in central Washington as a twin turboprop plane cruises southward. Through the cabin window, the jagged peaks of the Cascades rise in the west; to the east, a lush carpet of green vineyards and yellow wheat fields. But an hour into this flight, the blue skies give way to a white haze that rapidly turns to an alarming burnt orange.
The cabin begins to reek of smoke. The plane’s vibrations increase until the entire vessel is rocking and rolling. For a few seconds, the plane is literally free falling. All the while, outside the window, the sky grows darker and darker.
It’s another day at work for Arthur Sedlacek, an atmospheric chemist who is trying to solve one of the biggest mysteries in global climate change: the role that wildfires play when they spew millions of tons of soot skyward each year.
For five months in 2013, Sedlacek was part of a thrill-seeking team that flew into wildfire plumes in the Pacific Northwest and then Tennessee to measure exactly what’s in the soot. “Biomass burns are just this incredibly rich soup of raw material,” said Sedlacek, who is based at Brookhaven National Laboratory in New York.
It’s a tricky scientific problem because fires exert both warming and cooling effects on the climate.
Black smoke billowing up from a fire’s center has a warming effect because dark aerosols absorb light, keeping that energy trapped in our atmosphere. But as winds push aerosols away from the fire, the particles gather a reflective coating of organic matter, which has a cooling effect. White aerosols scatter light, sending that energy back into space.
So the smoke from wildfires can impact the climate directly, by reflecting and absorbing sunlight, and also indirectly, by influencing the formation of clouds. But how will these effects change as the frequency of wildfires increases in a warmer, drier world?
“That’s the million-dollar question,” Lewis said.
To try to answer that question as precisely as possible, Sedlacek, Lewis and their colleagues sampled 17 wildfires, seven urban plumes, and more than three dozen agricultural burns during 120 hours of flight time in 2013. Their research project is funded by the U.S. Department of Energy.
Sedlacek recalls one mid-summer flight that got especially hairy. “I remember about this time, hanging on, and thanking God I listened to the pilot when he said ‘buckle up’ because one of my colleagues had not and he went flying.” But that wasn’t the worst of it. In the thick of the plume the flight got even bumpier. Sedlacek overheard his pilot pleading with his engine, saying “stay with me baby, stay with me.”
As soon as the aircraft safely landed, Sedlacek pulled the pilot aside to ask why he was so worried about the engine. The pilot explained that aircraft engines need oxygen to burn fuel, and there’s very little oxygen in a smoke plume.”