Long-term MODIS observations reveal regional and seasonal variations in marine cloud brightening potential: a favorable coordinated response in the North Pacific during autumn

Marine cloud brightening (MCB) is a proposed solar radiation modification approach that envisions seeding sea-salt aerosols into selected marine low-cloud regions to reduce cloud droplet size and increase cloud albedo, thereby enhancing the reflection of incoming shortwave solar radiation. However, real-world cloud systems exhibit highly heterogeneous and environmentally dependent responses, and not all ocean regions are suitable candidates for MCB.

Recently, Science China Earth Sciences published a study by doctoral student Liya Niu, Professor Chuanfeng Zhao, and colleagues from the Department of Atmospheric and Oceanic Sciences at Peking University. Using daily observations collected from 2003 to 2024 by the MODIS instruments aboard the Terra and Aqua satellites, the research team systematically analyzed the spatiotemporal distributions and correlations of aerosol optical depth (AOD), cloud droplet effective radius (CER), cloud optical thickness (COT), and cloud fraction (CF) between 60°S and 60°N. The researchers identified preliminary candidate ocean regions that met the basic physical conditions for MCB and quantified the statistical distributions of the sensitivities of low-cloud properties to AOD across five representative ocean regions.

The results showed that CER and AOD were significantly negatively correlated across approximately 60% of the study domain, particularly over oceans with clean aerosol backgrounds, while CF and AOD were significantly positively correlated across approximately 95% of the domain. COT responses showed more pronounced regional and seasonal differences. Among the five candidate regions, CF and COT over the North Pacific during boreal autumn showed relatively strong positive sensitivities to AOD, while CER retained a negative sensitivity. The directions of all three responses were consistent with theoretical expectations. However, the sensitivity distributions were broad, indicating that high mean sensitivity does not imply equally consistent or predictable responses throughout a region.

The ocean regions also displayed distinct statistical response patterns. In the South Pacific, CF and COT showed positive sensitivities to AOD during some seasons, but CER also showed a positive sensitivity, indicating a decoupling between macrophysical and microphysical cloud responses. During boreal winter, the North Atlantic showed weaker CF sensitivity but stronger COT sensitivity, a pattern that can be characterized as "limited cloud-area expansion but pronounced optical thickening". These differences indicate that MCB-related cloud responses are strongly dependent on region and season, and their underlying physical mechanisms require further examination.

The authors emphasize that assessments of MCB potential should not prioritize high sensitivity alone, but should also account for the consistency, robustness, and predictability of cloud responses. A more comprehensive assessment framework should incorporate aerosol type and vertical distribution, cloud regime, underlying surface characteristics, meteorological dynamical and thermodynamic conditions, and the evolution of the background climate state. The underlying causal mechanisms, realized radiative cooling efficacy, response stability, and potential risks remain to be further evaluated through process-oriented observations and model experiments, thereby providing a more robust scientific basis for the scientific evaluation and risk assessment of MCB.

The study was supported by the National Key Research and Development Program of China.

See the article:

Niu L, Zhao C, Zhang H, Liang Y, Chen A. 2026. Spatiotemporal characteristics of aerosols and low clouds from MODIS and their implications for marine cloud brightening. Science China Earth Sciences, 69(8): 2812-2823, https://doi.org/10.1007/s11430-025-1794-7