National & World News

Wildfires were so hot they cooled the planet

By Benjamin Storrow | 07/28/2021 05:51 AM EST

Wildfires in Australia had a global cooling effect last year, prompting climate scientists to reassess their computer models. Ian

“Wildfires are starting to affect climate,” said John Fasullo, a NCAR scientist and the lead author of

the paper. “As the Earth warms, they are going to become more and more important in understanding

our climate system.”

But, he added, “Understanding their broader role in the climate system and climate projections, that

is not something we have a good handle on.”

The research does not mean wildfires could curb climate change. The location of a fire is important

to determining its climatic impact. In the Northern Hemisphere, wildfires can speed warming. Ash

falling in the Arctic, for instance, can accelerate ice melt by darkening the snow and absorbing the

sun’s heat.

But the impact of the Australian bushfires was just the opposite.

Air quality is generally pristine in large swaths of the Southern Hemisphere. The bushfires added

large amounts of aerosols into the atmosphere, changing the composition of clouds to make them

more reflective of the sun’s rays. The cloud cover cooled the southern half of the planet, pushing

tropical thunderstorms northward. The NCAR researchers estimate the fires cooled the planet 0.06

degree Celsius.

By comparison, economic lockdowns associated with the pandemic are estimated to gradually warm

the planet 0.05 C by 2022. That, too, might appear counterintuitive.

Factories, power plants and cars emit carbon dioxide, which warms the planet over the course of

decades. But those same facilities also emit aerosols, which block the sun’s radiation and can fall

quickly out of the atmosphere. Those aerosols fell last year as factories ran less and cars remained

parked, causing the planet to warm slightly.

The annual temperature fluctuations of both events are slight. More important are the long-term

implications of increasingly intense fires, researchers said.

The impact of the Australian fires was similar to a major volcanic eruption, which can disrupt the

climate by sending plumes of particulate matter into the sky, Fasullo said. But where volcanic

eruptions of that magnitude tend to happen once every 30 years, fires like those that burned in

Australia are expected to become more common.

That points to the need for more research into the climate impacts of fire, so it can be incorporated

into climate models, he said.

“The way we’ve studied this so far has been really insufficient,” Fasullo said. “So that is what we’re

doing now in our research.”