Smoke from African agricultural fires brightens clouds over the southeast Atlantic—but new research from scientists at the University of Miami Rosenstiel School of Marine, Atmospheric and Earth Science shows that the same weather pattern carrying the smoke also thins and reduces cloud cover, effectively offsetting its cooling effect.
The findings, published in Nature Communications Earth & Environment, underscore the importance of atmospheric conditions when evaluating geoengineering strategies such as marine cloud brightening, a proposed approach that uses aerosols to make clouds more reflective and redirect sunlight back into space to produce a climate cooling effect.
"Millions of people live with wildfire smoke as a seasonal fact of life, including here in Miami," said Tyler Tatro, the lead author of the study and a doctoral student in the Department of Atmospheric Sciences at the Rosenstiel School. "Our study shows that smoke's effects on clouds depend on the weather carrying it, meaning the same fire can brighten or diminish clouds depending on atmospheric conditions."
Agricultural fires in Angola generate substantial smoke each year, contributing to southern Africa's significant share of global biomass-burning emissions. From June through August, this smoke is transported over the southeast Atlantic, where it interacts with extensive marine cloud decks. Smoke modifies the atmosphere it moves through, influencing cloud properties, sunlight, temperatures and, in some cases, rainfall.
To investigate these interactions, the research team combined observations from the Department of Energy's LASIC field campaign on Ascension Island and NASA's ORACLES aircraft campaign with weather and aerosol datasets. Using satellite observations and 20 years of reanalysis data (2003–2023), the researchers examined how seasonal weather patterns over Angola influence smoke transport and its interactions with the southeast Atlantic's marine cloud deck.
The study also highlights challenges in evaluating marine cloud brightening. The southeast Atlantic is one of the regions most frequently studied for the strategy, which would involve deliberately adding particles to low ocean clouds to increase their reflectivity. Researchers found that ship exhaust trails capable of brightening clouds are easier to detect when less smoke is present. This overlap could make shipping-related cloud brightening appear more effective than it actually is, emphasizing the need to account for background aerosol levels and atmospheric conditions when assessing potential climate-cooling interventions.
"Low clouds over the ocean represent the largest source of uncertainty in projections of future global warming," said Paquita Zuidema, the coauthor of the study and a professor and chair of the Department of Atmospheric Sciences. "The southeast Atlantic's extensive stratocumulus cloud deck is one of four major, semi-permanent subtropical low-cloud regions and the most seasonally polluted of the four, by smoke. Understanding how smoke interacts with these clouds is essential for interpreting climate trends and predicting how cloud cover may change as carbon dioxide levels rise, fire seasons shift and geoengineering strategies are considered."
The study, titled "Weak, shallow dry convection over Angola increases offshore stratocumulus cloud droplet number concentrations," was published on August 29, 2026, in the journal Nature Communications Earth & Environment. The authors are Tyler Tatro and Paquita Zuidema of the University of Miami Rosenstiel School.
The research was supported by NASA and Department of Energy Atmospheric System Research grants (NASA: 80NSSC21K1344; DOE ASR: DE-SC0021250).
