Where there's smoke, is there likely climate change?

Smoke can add to temporary warming during fire's height, but also can block sun, cooling the air

PASCO, Wash. — Researchers are flying over Western wildfires to sample the thick smoke they emit and study its role in cloud formation and climate.

The data-gathering campaign is intended to help scientists flesh out one of the least understood areas of climate: the role of aerosols, or particles given off by wildfires, and how they evolve over time.

Biomass burning, such as forest fires and agricultural fires when farmers burn off their farm fields, has long been known to release large amounts of carbon dioxide, a key greenhouse gas, but less is known about how smoke plumes evolve over time and affect climate.

The researchers already have flown over fires in Washington and Oregon. This week, they traveled to central Idaho, where a complex of fires has scorched some 400 square miles (256,000 acres) of grass and forestland.

So far, they're finding that the thick, black smoke emitted when a wildfire is burning hottest tends to have a warming effect on the climate, said Larry Kleinman, one of two principal investigators from Brookhaven National Laboratory.

However, as winds push them away from the fire, the particles gather a coating of reflective organic matter that has a cooling effect on the Earth, he said. Think of the white smoke you see over a smoldering fire.

That change can happen in just a couple of hours as the particles travel through the atmosphere, said Arthur Sedlacek, the other Brookhaven investigator.

Both stressed that they are still early in their research, though they hope to provide information that could be factored into large-scale climate models.

A tour of the research aircraft Wednesday showed a wall of instruments designed to measure, among other things, the size and chemical composition of particles, their light absorption and scattering effects, and the gases in the air. All of that is sucked in through small tubes outside the airplane.

Much like flying through thunderclouds, the bumpy flight is not often a friendly environment for sensitive measurements.

In addition, Kleinman said, flight restrictions sometimes limit how close they can fly to allow air tankers and helicopters to fight the fires. The researchers also must pore over detailed weather forecasts to map their flights, delaying their response.

Still, they've managed to fly into big plumes to collect large particles of black carbon soot and continue their travels downwind to gather smaller particles.

"It's surreal to go through the plume. You're in blues skies, then you hit a wall of white haze, then it's orange. And there's a lot of turbulence," Sedlacek said.

The researchers hope the field study will contribute to a better understanding of how particles emitted from different types of fires may contribute to climate change.

The study continues in the Northwest through mid-September. The researchers will travel to Tennessee in October to study smoke plumes from large agricultural plumes.


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