Cloud Microphysical Implications for Marine Cloud Brightening: The Importance of the Seeded Particle Size Distribution
Abstract
Marine cloud brightening (MCB) has been proposed as a viable way to counteract global warming by artificially increasing the albedo and lifetime of clouds via deliberate seeding of aerosol particles. Stratocumulus decks, which cover wide swaths of Earth’s surface, are considered the primary target for this geoengineering approach. The macroscale properties of this cloud type exhibit a high sensitivity to cloud microphysics, exposing the potential for undesired changes in cloud optical properties in response to MCB. In this study, we apply a highly detailed Lagrangian cloud model, coupled to an idealized parcel model as well as a full three-dimensional large-eddy simulation model, to show that the choice of seeded particle size distribution is crucial to the success of MCB, and that its efficacy can be significantly reduced by undesirable microphysical processes. The presence of even a small number of large particles in the seeded size spectrum may trigger significant precipitation, which will reduce cloud water and may even break up the cloud deck, reducing the scene albedo and hence counteracting MCB. On the other hand, a seeded spectrum comprising a large number of small particles reduces the fraction of activated cloud droplets and increases entrainment and evaporation of cloud water, which also reduces the efficiency of MCB. In between, there may exist an aerosol size distribution that minimizes undesirable microphysical processes and enables optimal MCB. This optimal size distribution is expected to be case dependent.
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For MCB, uncertainties persist in aerosol-cloud interactions under real marine conditions, particularly the efficiency of sea-salt particles in brightening clouds without triggering precipitation.
“For MCB, uncertainties persist in aerosol-cloud interactions under real marine conditions, particularly the efficiency of sea-salt particles in brightening clouds without triggering precipitation”
From Past Field Experiments of Solar Radiation Modification: A Review of the Scientific and Technical Aspects for Governance (2026) · cites this paper as Hoffmann & Feingold, 2021
GCCN act as precipitation nuclei by accelerating collision-coalescence processes: their large, hydrated droplets (>30 μm at cloud saturation) lower the barrier for droplet collisions, triggering premature raindrop formation and subsequent cloud water loss, which can offset brightening efficacy.
“GCCN act as precipitation nuclei by accelerating collision-coalescence processes: their large, hydrated droplets ( > 30 μm at cloud saturation) lower the barrier for droplet collisions, triggering premature raindrop formation and subsequent cloud water loss, which can offset brightening efficacy (e.g., Feingold et al., 1999; Hoffmann & Feingold, 2021)”
From Past Field Experiments of Solar Radiation Modification: A Review of the Scientific and Technical Aspects for Governance (2026) · cites this paper as Hoffmann & Feingold, 2021
Meteorological variability, such as wind shifts (dispersing seeded plumes), low wind speeds <2 m/s (causing aerosol stagnation), or cloud breakup (disrupting stratocumulus homogeneity), served as universal triggers for operational pauses.
“For instance, meteorological variability, such as wind shifts (dispersing seeded plumes), low wind speeds < 2 m/s (causing aerosol stagnation), or cloud breakup (disrupting stratocumulus homogeneity), served as universal triggers for operational pauses (e.g., Bates et al., 2013; Hoffmann & Feingold, 2021)”
From Past Field Experiments of Solar Radiation Modification: A Review of the Scientific and Technical Aspects for Governance (2026) · cites this paper as Hoffmann & Feingold, 2021
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References 65 · Cited by 65
- Authors
- Hoffmann, F., & Feingold, G.
- Affiliations
- Cooperative Institute for Research in Environmental Sciences (US)
- NOAA Chemical Sciences Laboratory (US)
- Venue
- Journal of the Atmospheric Sciences
- Publisher
- American Meteorological Society
- Published
- 2021-10
- Volume
- 78
- Issue
- 10
- Pages
- 3247-3262
- ISSN
- 0022-4928 (ISSN-L)
- 1520-0469
- OpenAlex
- W3184550635
- Cited by
- 65
- References
- 65
- Citations by year
- 2026: 6 · 2025: 15 · 2024: 9 · 2023: 21 · 2022: 9 · 2021: 5
- FWCI
- 4.51
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- Journal of the Atmospheric Sciences (publishedVersion)
- NOAA Institutional Repository (submittedVersion)
- Funders
- Deutsche Forschungsgemeinschaft (HO 6588/1-1)
- Climate Program Office (#03-01-07-001)
- Topics
- Physical Sciences › Environmental Science › Global and Planetary Change › Atmospheric aerosols and clouds
- Physical Sciences › Environmental Science › Global and Planetary Change › Climate Change and Geoengineering
- Physical Sciences › Earth and Planetary Sciences › Atmospheric Science › Meteorological Phenomena and Simulations
- Keywords
- marine cloud brightening, particle size distribution, cloud microphysics, stratocumulus clouds, geoengineering, cloud albedo, cloud lifetime, precipitation, cloud droplet activation, large eddy simulation, Lagrangian cloud model
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