Mid-level clouds at the top of a smoke layer overlie the lower stratocumulus deck below. Phot taken off the coast of Angola, September, 2016.
Photo Credit: Paquita Zuidema, Ph.D.
Scientific Frontline: Extended "At a Glance" Summary: African Smoke and Cloud Brightening
The Core Concept: Smoke from agricultural fires in Africa brightens marine clouds, but the same weather patterns that transport the smoke also thin and reduce cloud cover, offsetting the smoke's cooling effect.
Key Distinction/Mechanism: The aerosol effect of smoke makes clouds more reflective (brightening), which should produce a cooling effect by redirecting sunlight back into space. However, atmospheric conditions, specifically the weather patterns carrying the smoke from Angola over the southeast Atlantic, concurrently diminish the cloud deck, counteracting the expected cooling.
Major Frameworks/Components:
- Biomass-burning emissions from African agricultural fires.
- Aerosol-cloud interactions and their influence on cloud properties, sunlight, and temperatures.
- The southeast Atlantic's extensive stratocumulus cloud deck.
- Observations from the Department of Energy's LASIC field campaign and NASA's ORACLES aircraft campaign, combined with 20 years of reanalysis data (2003–2023).
Branch of Science: Atmospheric Science, Climatology, Environmental Science.
Future Application: The findings emphasize the necessity of factoring in atmospheric conditions and background aerosol levels when assessing the viability and effectiveness of geoengineering strategies, specifically marine cloud brightening (deliberately adding particles to low ocean clouds to increase reflectivity).
Why It Matters: Low clouds over the ocean represent a major source of uncertainty in future global warming projections. Understanding how smoke interacts with the stratocumulus cloud deck is essential for interpreting climate trends and predicting changes in cloud cover as carbon dioxide levels rise and fire seasons shift.
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, 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, coauthor of the study and professor and chair of the Department of Atmospheric Sciences. “The Southeast Atlantic’s extensive stratocumulus cloud deck is one of four major, semipermanent 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.”
Funding: The research was supported by NASA and Department of Energy Atmospheric System Research grants (NASA: 80NSSC21K1344; DOE ASR: DE-SC0021250).
Published in journal: Nature Communications Earth & Environment
Authors: Tyler Tatro, and Paquita Zuidema
Source/Credit: Rosenstiel School of Marine and Atmospheric Science | Annie Reisewitz
Edited by: Scientific Frontline
Reference Number: as091926_01