CERN CLOUD Study Reveals Marine Phytoplankton Boost Climate-Resilient Aerosols

Aerosols act as cloud condensation nuclei (CCN), reflecting sunlight and brightening clouds. Historically, sulfur dioxide from fossil-fuel combustion generated sulfuric acid, a primary nucleating vapor. Emission controls have cut atmospheric sulfur dioxide, improving public health but reducing this cooling aerosol pool. Earlier CLOUD experiments identified isoprene-driven particle formation over tropical rainforests, highlighting the need to map natural aerosol sources.

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The study was led by Jasper Kirkby, co-author and senior scientist of the CLOUD Collaboration at CERN. Gautier Hamel de Monchenault, CERN Director for Research and Computing, provided senior oversight. The CLOUD Collaboration, a multidisciplinary team at the European Organization for Nuclear Research, combines laboratory experiments with atmospheric modeling.

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Marine phytoplankton emit dimethyl sulfide (DMS), which oxidizes to sulfuric acid (SA) and methanesulfonic acid (MSA). Laboratory and computer-model results show that below –10 °C, MSA alone can nucleate particles as efficiently as SA, and below +10 °C it drives particle growth even with minimal ammonia. The coexistence of MSA and SA in cool marine regions suggests a previously unaccounted source of CCN.

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• Approximately 20 % of atmospheric sulfur originates from phytoplankton-derived DMS.

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• MSA-driven nucleation rates may be up to tenfold higher, and growth rates up to twofold higher, than those from SA and ammonia alone.

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• MSA and SA are present at comparable concentrations in cool oceanic air masses.

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• The peer-reviewed paper “Role of Methanesulfonic Acid in Atmospheric Particle Nucleation and Growth” was published in *Nature* on June 24, 2026.

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Model simulations indicate that incorporating MSA-driven nucleation could close a major gap in current climate models, potentially lowering estimates of Earth’s climate sensitivity and moderating projected warming. The biosphere’s capacity to generate CCN without anthropogenic emissions suggests a natural resilience that may partially offset greenhouse-gas forcing.

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CERN Director Gautier Hamel de Monchenault described the work as “an important advance in our understanding of climate,” emphasizing that enhanced biogenic CCN will affect climate-sensitivity estimates and warming projections. Study authors stress that future climate assessments must explicitly include biogenic aerosol sources to improve predictive reliability.

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Sulfur dioxide particles, while cooling, are linked to lung and heart disease. Reducing sulfur emissions improves public health but, according to the researchers, may inadvertently diminish aerosol-mediated cooling, creating a policy “catch-22” between health benefits and climate mitigation.

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The study quantifies a potential tenfold increase in nucleation rates, yet the exact magnitude of the resulting global cooling offset remains uncertain. Current climate models lack this biogenic pathway, and further observational data are needed to validate modelled impacts.

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• “However, it is vital to understand and properly account for biogenic sources to reliably predict the Earth’s future climate and air quality.” — Jasper Kirkby, CLOUD Collaboration

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• “Since MSA and SA generally coexist at similar concentrations in cool marine regions, our findings indicate that particle nucleation rates might be accelerated up to tenfold and growth rates up to twofold compared with sulphuric acid and ammonia alone,” — Jasper Kirkby

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• “The CLOUD Collaboration has made an important advance in our understanding of climate” — Gautier Hamel de Monchenault, CERN Director for Research and Computing

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• “Our model simulations indicate that MSA-driven new particle formation may account for the major missing source of marine aerosol particles in current models.” — Jasper Kirkby

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The collaboration plans to integrate MSA-driven nucleation into global climate models, expand field measurements over the Southern Ocean, and assess policy scenarios that balance aerosol-related cooling with health-focused emission reductions.

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