Can wildfires cool the climate?

Tiny airborne particles, like those spewed by forest fires, can alter Earth’s temperature

Wildland fires generate intense heat. But plumes of the sooty smoke that they emit can rise to high altitudes. There it can block out much of the sun’s light, causing a ground-level cooling.

Wildfires have captured headlines around the globe in recent years. In 2018, California wildfires caused record destruction and death. But the area they incinerated would be eclipsed by fires in 2020. Some of those fires roared out of control for weeks in a swath that spanned the U.S. West Coast, from Canada down to Mexico. And a surprise 2020 outbreak of wildfires across the Siberian Arctic incinerated grasslands and tundra.

These intense and widespread fires worry scientists. And for many reasons. Besides causing billions of dollars in property damage, they can erase the habitat of valued wildlife. They also fill the air with choking pollution. And when they burn near cities, they put the lives of whole communities in danger. The November 2018 Camp Fire was the deadliest in California history. Within days it wiped out 18,800 buildings, including much of Paradise, Calif. Some infernos even burn so hot that they can spawn firenadoes.

But scientists are interested in these fires for yet another reason. The black carbon-rich smoke billowing from their flames is made of the soot and ash from burned trees, grass and shrubs. The intense heat of some infernos can propel this soot and ash to altitudes so high that it can circumnavigate the globe. And the warming sunlight absorbed by dark particles at high altitudes won’t reach Earth’s surface.

Scientists refer to those tiny airborne particles of soot, dust and more as aerosols (AIR-oh-sahls). One important trait is how well they reflect light. Albedo is the term for this. Snow and white ice have a high albedo; they reflect the most light. Tar and asphalt have a low albedo, absorbing the sun’s light, mostly as heat. So the color of aerosols is important.

Whether we’re aware of them or not, aerosols are everywhere. And they can play a major role in where sunlight has its greatest impact on Earth’s temperature.

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