African agricultural fires release large amounts of smoke that can brighten clouds over the southeast Atlantic, according to a study from the University of Miami Rosenstiel School of Marine, Atmospheric and Earth Science. This occurs because the smoke particles act as cloud condensation nuclei, which can make clouds more reflective. However, the same weather systems that carry the smoke also reduce cloud cover, which cancels out the cooling effect of the brighter clouds. The findings, published in Nature Communications Earth & Environment, emphasize the complexity of evaluating geoengineering techniques like marine cloud brightening, which aim to cool the planet by making clouds more reflective and reflecting more sunlight back into space. A significant portion of global biomass-burning emissions comes from fires in southern Africa, particularly in Angola. Between June and August, smoke from these fires is carried by wind patterns over the southeast Atlantic, where it interacts with vast layers of marine clouds. Researchers used data from the Department of Energy’s LASIC field campaign on Ascension Island and NASA’s ORACLES aircraft campaign, along with weather and aerosol records, to study these interactions. By combining satellite observations with 20 years of reanalyzed data (2003–2023), the team examined how seasonal weather patterns in Angola influence the movement of smoke and its effects on the region’s cloud cover. The study highlights a key challenge in assessing marine cloud brightening. The southeast Atlantic is one of the most studied regions for this geoengineering strategy, yet the presence of smoke can complicate measurements. Researchers found that cloud brightening caused by ship exhaust—another potential method for cooling the climate—is more easily detected when there is less smoke in the air. This overlap may make it appear that shipping-related cloud brightening is more effective than it actually is. Therefore, scientists stress the importance of accounting for background aerosol levels and atmospheric conditions when evaluating climate-cooling interventions. Low clouds over the ocean are a major source of uncertainty in climate models predicting future global warming. The southeast Atlantic is home to one of the largest and most persistent low-cloud systems, known as a stratocumulus cloud deck. This region is also the most affected by smoke pollution among the four major subtropical cloud regions. Understanding how smoke interacts with these clouds is crucial for interpreting climate trends and predicting how cloud cover might change as carbon dioxide levels rise, fire seasons shift, and new geoengineering strategies are explored.