A bold truth: wildfire smoke can rise high enough to cool Earth, not just darken skies. But here’s where it gets controversial: the far-reaching climate impact of those lofted plumes is still full of surprises.
Wildfires do more than burn vegetation; some are violent enough to generate their own weather, including pyrocumulonimbus thunderstorms that loft smoke as high as 10 miles (16 kilometers) into the atmosphere. For a long time, scientists suspected this high-altitude smoke could linger for weeks or months, yet measuring its climate effect proved tricky because sampling was so challenging. Now, researchers have finally obtained direct measurements.
A team of atmospheric scientists from the Harvard John A. Paulson School of Engineering and Applied Sciences captured five-day-old wildfire smoke in the upper troposphere, roughly nine miles (14.5 kilometers) above the planet. They found large smoke particles—about 500 nanometers in diameter—that are not currently represented in climate models. Remarkably, these bigger particles appear to cool the atmosphere rather than warm it.
Within the smoke cloud, aerosols of this substantial size form through coagulation, a process made efficient by the region’s slow air mixing. Lead author Yaowei Li explains that in this specific layer, smoke particles stay concentrated and collide more frequently, accelerating coagulation. This detail helps explain why these particles behave differently from their lower-atmosphere counterparts.
The size and behavior of these aerosols influence how much solar radiation reaches Earth’s surface: they can either absorb sunlight or reflect it back into space. In this study, the larger, coagulated particles increased outgoing radiation by about 30% to 36% compared with lower-altitude particles, producing a detectable cooling effect that existing climate models do not capture.
Researchers emphasize that more work is needed to understand the full implications for weather and climate. Co-author and project scientist John Dykema notes that these large particles could alter atmospheric circulation by causing localized heating, potentially shifting jet streams. “All of these possibilities exist, and we don’t yet know which way they might go,” he says.
This finding opens new questions about the role of high-altitude wildfire smoke in climate dynamics and whether current models underestimate or overlook these cooling effects.
Published on December 10 in Science Advances, the study invites ongoing discussion about how to integrate such complex particle behavior into climate predictions—and what that means for policy and public understanding of wildfire impacts.
If you have thoughts or a perspective on how high-altitude smoke should influence climate policy or weather forecasting, share your view in the comments. Do you find the potential cooling effect convincing, or do you worry about unintended consequences elsewhere in the atmosphere?
Note: this rewrite preserves all original information and key findings while presenting them in a fresh, accessible way for readers new to the topic.
