Bold claim: wildfire smoke rising miles into the atmosphere can cool Earth’s climate in ways traditional models miss. And this is the part most people miss—high-altitude smoke doesn’t just drift away; it forms unusually large particles that reflect more sunlight back to space, producing a measurable cooling effect.
Wildfires aren’t only about scorching landscapes. Some fires become so intense they generate their own weather, including pyrocumulonimbus storms that lift smoke up to about 10 miles (16 kilometers) high. For a long time, scientists suspected that these high-altitude plumes persisted for weeks or months, but measuring their climate impact proved tricky—until now.
Researchers from Harvard’s John A. Paulson School of Engineering and Applied Sciences report the first direct measurements of wildfire smoke five days after emission in the upper troposphere, roughly nine miles (14.5 kilometers) above the planet. They found unusually large smoke particles, around 500 nanometers in diameter—about twice the size of typical wildfire aerosols at lower altitudes—which are not currently represented in climate models. The team proposes that this larger size arises from efficient coagulation, where particles merge as they mix slowly in the stable, high-altitude air, allowing them to collide and stick together more readily.
These big aerosols influence the radiation balance reaching and leaving Earth. In this study, the larger particles increased outgoing longwave and shortwave radiation by about 30% to 36% relative to what smaller, lower-altitude particles would produce, signaling a notable cooling effect that existing models don’t account for.
But more work is needed. Co-author and project scientist John Dykema notes that such large, coagulated particles could alter atmospheric circulation by creating localized heating, potentially shifting jet streams. He emphasizes that we don’t yet know which directions these effects might take.
This finding adds a new layer to our understanding of wildfire impacts on climate. It suggests that high-altitude smoke could offset some warming, at least regionally or temporarily, and it highlights the importance of integrating these high-altitude processes into climate projections.
The study was published on December 10 in Science Advances. As researchers continue to investigate, questions remain: How widespread are these high-altitude coagulated particles across different fire regimes? Do regional precipitation patterns change as a result? And what lessons can we draw for improving climate models to reflect these altitudinal effects?
What’s your take on high-altitude wildfire smoke—could it be a natural brake on warming, or does this cooling effect get swamped by other atmospheric processes? Share your thoughts in the comments.
