A new preprint study submitted to Nature Communications suggests that pollution and wildfire aerosols don’t cool the atmosphere right away — they may actually warm it first. Led by Guy Dagan of Hebrew University of Jerusalem, the research found that sudden spikes in aerosol concentrations can trap heat for up to 48 hours before the particles’ well-known cooling effect begins to take hold.
Study finds aerosols warm the atmosphere before cooling it
The preprint directly challenges the assumption that aerosols begin lowering temperatures the moment they enter the atmosphere. Professor Guy Dagan and his team at Hebrew University of Jerusalem ran a series of climate simulations, tracking atmospheric conditions across the days following sudden increases in aerosol concentrations.
The results were unambiguous. Heat remained trapped for roughly the first 48 hours after a pollution spike, with peak warming — reaching approximately 20 watts per square meter — concentrated in that first day. Only after that initial window did the particles’ well-known cooling properties begin to assert themselves.
Cloud changes drive the short-term warming effect
The mechanism behind this temporary warming comes down to how aerosols interact with clouds. When particle concentrations rise sharply, they suppress light rain, pushing more water vapor higher into the atmosphere than would otherwise occur. At those altitudes, the extra moisture promotes the formation of additional ice crystals and high-altitude clouds — structures that act as a thermal blanket, trapping outgoing heat that would normally escape into space.
Once the cloud response begins to fade after roughly 48 hours, the picture shifts. The aerosols’ reflective properties, which bounce incoming sunlight back away from Earth’s surface, become the dominant force, and the net atmospheric effect moves toward cooling.
Findings challenge how climate models and satellite data are interpreted
Aerosols are already among the most difficult variables in climate science. Their interactions with clouds introduce substantial uncertainty into forecasting models, and this study suggests that uncertainty may run deeper than previously understood.
Timing is the core issue. Many climate models and satellite observation methods rely on measurements taken at a single moment. If the atmosphere needs days — not minutes — to fully respond to a pollution event, a snapshot captured too early could reflect only the warming phase, while one taken too late might show only cooling. Neither would tell the whole story. Dagan put it plainly in a university news release: “The atmosphere has a memory.” That framing carries real weight for how researchers design observational studies and interpret what they collect.
Frequent pollution fluctuations may prevent full cooling from occurring
Pollution levels don’t spike once and then stabilize — they shift constantly, driven by traffic, industry, wildfires, and weather patterns. If a new pollution spike arrives while the atmosphere is still working through its response to the previous one, the system never fully reaches the cooling phase.
The study suggests that when these fluctuations occur every few days, the net climate impact of aerosols could differ significantly from what current estimates assume. Repeated spikes may keep the atmosphere cycling through warming phases before cooling ever fully takes hold, meaning pollution’s net effect on the climate could be less cooling — and more warming — than models currently account for.
Pollution needs to be assessed over time
This study introduces an important temporal dimension to how scientists think about aerosols. A sudden increase in pollution or wildfire smoke can warm the atmosphere for up to 48 hours before any cooling effect begins — warming driven by cloud changes at high altitude, not by the aerosols’ reflective properties.
The implications cut in two directions. Single-moment measurements, whether from satellites or models, may systematically misrepresent aerosols’ climate role depending on when they are taken. And because real-world pollution levels fluctuate continuously, the atmosphere may rarely complete a full warming-to-cooling cycle before the next spike arrives. The study is currently a preprint and has not yet completed peer review, but it raises substantive questions about one of climate science’s most uncertain variables — ones that researchers and modelers may need to account for when assessing how pollution events shape atmospheric temperatures over time.
Kelly is an experienced writer with 15 years of experience exploring the big stories that shape our world, from tech breakthroughs and space exploration to climate, energy, and the fascinating quirks of science. She has a talent for turning complex ideas into sharp, memorable insights that stay with readers long after they’ve finished reading.
