Detectable ship tracks account for just 5% of aerosol indirect forcing from ship emissions

Journal Article · Fri Nov 14 00:00:00 EST 2025 · Communications Earth & Environment

DOI:https://doi.org/10.1038/s43247-025-02825-w· OSTI ID:3004789

Yuan, Tianle ^[1]; Song, Hua ^[2]; Boss, Lili F. ^[3]; Diamond, Michael S. ^[3]

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1. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States); Univ. of Maryland Baltimore County (UMBC), Baltimore, MD (United States)
2. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States); Science Systems and Applications, Inc. (SSAI), Lanham, MD (United States)
3. Florida State Univ., Tallahassee, FL (United States)

Ship emissions are a major source of aerosols over oceans, affecting both air quality and energy balance of the climate. However, estimates of their climate forcing diverge between studies relying on visible ship-tracks and those based on models. Here we show that forcing due to visible ship-tracks accounts for just 5% of the total forcing over the southeast Atlantic shipping-lane. Most forcing from ship emissions comes from aerosols that do not form detectable ship-tracks. They are only tips of the iceberg. We make three forcing calculations, one bottom-up based on visible ship-tracks, one top-down based on spatial relationships, and a hybrid approach that combines top-down or model estimated cloud droplet number concentration changes and cloud adjustments. Although the forcing based on machine learning detected ship tracks is an order of magnitude greater than prior results using manually detected ship-tracks, it remains only 5% of that inferred by top-down or cloud adjustment based methods for pre-2020 shipping. The top-down and the combined cloud adjustments methods show similar forcing for the post-2020 reduction in ships’ sulfur emission, although the methods have important regional differences in cloud adjustments that need further investigation. Our results reconcile a long-standing discrepancy in the literature and have important implications for aerosol indirect forcing and marine cloud brightening.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Atmospheric Radiation Measurement (ARM) Data Center
• Sponsoring Organization: National Aeronautics and Space Administration (NASA); National Oceanic and Atmospheric Administration (NOAA); USDOE Office of Science (SC), Biological and Environmental Research (BER)
• Contributing Organization: Argonne National Laboratory (ANL), Argonne, IL (United States); Brookhaven National Laboratory (BNL), Upton, NY (United States); Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
• Grant/Contract Number: AC05-00OR22725; SC0024078
• OSTI ID: 3004789
• Journal Information: Communications Earth & Environment, Journal Name: Communications Earth & Environment Journal Issue: 1 Vol. 6; ISSN 2662-4435
• Publisher: Springer Nature
• Country of Publication: United States
• Language: English