As wildfires become more common and intense, it's becoming critical to understand how they affect the climate. And according to newly accepted data from University of Wyoming (UW) researchers, climate models that have been used for years likely had some key things wrong with them.
"One of our grad students just got accepted a paper discussing how wildfire smoke in general in global climate models is too dark to absorb. That just got accepted into Nature Communications," said Principal Investigator Shane Murphy.
The Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption and Nitrogen (WE-CAN) field campaign started in 2018 when UW researchers joined others from the University of Washington, Colorado State University (CSU), University of Montana, and the National Center for Atmospheric Research (NCAR) in Boulder, Colorado. It was led by CSU.
The scientists flew through wildfire smoke plumes in a C-130 aircraft retrofitted with scientific instruments that was based in Boise, Idaho. It's a large plane, but each team installed their own sets of instruments which made for a tight squeeze.
"Once all that instrumentation is on there, there's just an aisle left in the middle for you to walk up and down," said Murphy. "And then pretty much the whole rest of the plane is crammed with instrumentation with a little room left for the scientist to sit and turn and operate it. And then up in the front of the plane, one research scientist, so that would vary from flight to flight, will direct the flight."
The highly-skilled pilots maneuvered the plane through smoke that was often too thick to see where they were going, which meant they relied on instrument controls instead of visual controls. According to Murphy, they were sometimes given their own airspace to fly in so they didn't have to worry about crashing into firefighting planes.
"You know, you'd think it'd be scary, but it's actually not very scary because the pilots are just so competent from NCAR, they're really highly trained, and so they're always on top of it," said Murphey. "And the air traffic controllers are just really, really good about keeping the different aircraft isolated from one another. So you're really never worried about crashing into another aircraft."
As the plane navigated, the researchers gathered samples from different parts of the plume. Most flights were around eight hours long and focused on the western part of the country.
"We measured fires in California, Oregon, Washington, Utah, Montana. Wyoming, we might have snuck in. But we'd take off at Boise and the farthest flight we did was to measure the fire impacts on clouds off the coast of California, down by the bay area," said Murphy.
The institutions each focused on collecting a certain type of data. The UW team specifically looked at the color of the smoke particles, how they reacted to sunlight, and how long they stayed in the atmosphere.
There are three types of carbon, all with their own unique properties. Soot, or black carbon, tends to absorb a lot of sunlight. Light carbon is an aerosol that reflects sunlight. But brown carbon is another aerosol that's an "in-between" color that researchers still don't know very much about.
"You have to know how bright or dark is the smoke, and how bright or dark is the surface underneath. And when you have those two answers, you can figure out whether the smoke is on average warming or on an average cooling," said Murphey.
Most data models assume that smoke has a neutral effect on the climate. This new data suggests otherwise and will help ensure accurate climate models and predictions.
"So we can plan better. We understand if it's going to be more warming or cooling, and can react accordingly," said Murphey. "And these things also impact weather. It also helps us understand how wildfire smoke will impact cloud formation and weather systems and all of this."
The team presented its data on how fast brown carbon decays at the American Geophysical Union's virtual fall conference in early December. The data from this project is still being analyzed, but findings are being published as they come available.
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