Preprints
https://doi.org/10.5194/egusphere-2024-2547
https://doi.org/10.5194/egusphere-2024-2547
03 Sep 2024
 | 03 Sep 2024

Observational Constraints Suggest a Smaller Effective Radiative Forcing from Aerosol-Cloud Interactions

Chanyoung Park, Brian J. Soden, Ryan J. Kramer, Tristan S. L’Ecuyer, and Haozhe He

Abstract. The effective radiative forcing due to aerosol-cloud interactions (ERFaci) is difficult to quantify, leading to large uncertainties in model projections of historical forcing and climate sensitivity. In this study, satellite observations and reanalysis data are used to examine the low-level cloud radiative responses to aerosols. While some studies it is assumed that the activation rate of cloud droplet number concentration (Nd) in response to variations in sulfate aerosols (SO4) or the aerosol index (AI) has a one-to-one relationship in the estimation of ERFaci, we find this assumption to be incorrect, and demonstrate that explicitly accounting for the activation rate is crucial for accurate ERFaci estimation. This is corroborated through a “perfect-model” cross validation using state-of-the-art climate models, which compares our estimates with the “true” ERFaci. Our results suggest a smaller and less uncertain value of the global ERFaci than previous studies (-0.39 ± 0.29 W m-2 for SO4 and -0.24 ± 0.18 W m-2 for AI, 90 % confidence), indicating that ERFaci may be less impactful than previously thought. Our results are also consistent with observationally constrained estimates of total cloud feedback and “top-down” estimates that models with weaker ERFaci better match the observed hemispheric warming asymmetry over the historical period.

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Journal article(s) based on this preprint

14 Jul 2025
| ACP Letters
| Highlight paper
Observational constraints suggest a smaller effective radiative forcing from aerosol–cloud interactions
Chanyoung Park, Brian J. Soden, Ryan J. Kramer, Tristan S. L'Ecuyer, and Haozhe He
Atmos. Chem. Phys., 25, 7299–7313, https://doi.org/10.5194/acp-25-7299-2025,https://doi.org/10.5194/acp-25-7299-2025, 2025
Short summary Executive editor
Chanyoung Park, Brian J. Soden, Ryan J. Kramer, Tristan S. L’Ecuyer, and Haozhe He

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on egusphere-2024-2547', Erin Raif, 16 Oct 2024
    • AC3: 'Reply on CC1', Chanyoung Park, 04 Dec 2024
      • AC6: 'Reply on AC3', Chanyoung Park, 04 Dec 2024
  • RC1: 'Comment on egusphere-2024-2547', Anonymous Referee #1, 25 Oct 2024
    • AC1: 'Reply on RC1', Chanyoung Park, 04 Dec 2024
      • AC4: 'Reply on AC1', Chanyoung Park, 04 Dec 2024
  • RC2: 'Comment on egusphere-2024-2547', Anonymous Referee #2, 29 Oct 2024
    • AC2: 'Reply on RC2', Chanyoung Park, 04 Dec 2024
      • AC5: 'Reply on AC2', Chanyoung Park, 04 Dec 2024

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on egusphere-2024-2547', Erin Raif, 16 Oct 2024
    • AC3: 'Reply on CC1', Chanyoung Park, 04 Dec 2024
      • AC6: 'Reply on AC3', Chanyoung Park, 04 Dec 2024
  • RC1: 'Comment on egusphere-2024-2547', Anonymous Referee #1, 25 Oct 2024
    • AC1: 'Reply on RC1', Chanyoung Park, 04 Dec 2024
      • AC4: 'Reply on AC1', Chanyoung Park, 04 Dec 2024
  • RC2: 'Comment on egusphere-2024-2547', Anonymous Referee #2, 29 Oct 2024
    • AC2: 'Reply on RC2', Chanyoung Park, 04 Dec 2024
      • AC5: 'Reply on AC2', Chanyoung Park, 04 Dec 2024

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload
AR by Chanyoung Park on behalf of the Authors (04 Dec 2024)  Author's response   Author's tracked changes   Manuscript 
ED: Referee Nomination & Report Request started (04 Jan 2025) by Timothy Garrett
RR by Anonymous Referee #1 (31 Jan 2025)
ED: Reconsider after major revisions (04 Feb 2025) by Timothy Garrett
AR by Chanyoung Park on behalf of the Authors (25 Feb 2025)  Author's response   Author's tracked changes   Manuscript 
ED: Publish subject to minor revisions (review by editor) (13 Mar 2025) by Timothy Garrett
AR by Chanyoung Park on behalf of the Authors (20 Mar 2025)  Author's response   Author's tracked changes   Manuscript 
ED: Publish as is (29 Mar 2025) by Timothy Garrett
ED: Publish subject to minor revisions (review by editor) (04 Apr 2025) by Ken Carslaw (Executive editor)
AR by Chanyoung Park on behalf of the Authors (08 Apr 2025)  Author's response   Author's tracked changes   Manuscript 
ED: Publish as is (15 Apr 2025) by Ken Carslaw
ED: Publish as is (15 Apr 2025) by Ken Carslaw (Executive editor)
AR by Chanyoung Park on behalf of the Authors (15 Apr 2025)  Manuscript 

Journal article(s) based on this preprint

14 Jul 2025
| ACP Letters
| Highlight paper
Observational constraints suggest a smaller effective radiative forcing from aerosol–cloud interactions
Chanyoung Park, Brian J. Soden, Ryan J. Kramer, Tristan S. L'Ecuyer, and Haozhe He
Atmos. Chem. Phys., 25, 7299–7313, https://doi.org/10.5194/acp-25-7299-2025,https://doi.org/10.5194/acp-25-7299-2025, 2025
Short summary Executive editor
Chanyoung Park, Brian J. Soden, Ryan J. Kramer, Tristan S. L’Ecuyer, and Haozhe He
Chanyoung Park, Brian J. Soden, Ryan J. Kramer, Tristan S. L’Ecuyer, and Haozhe He

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Short summary
This study addresses the challenge of quantifying the impact of aerosol-cloud interactions. By analyzing satellite data and reanalysis, we examine cloud responses to aerosols by incorporating aerosol-to-cloud droplet activation rates. Our "perfect-model" validation reveals a smaller, less uncertain impact of aerosol-cloud interactions than previously estimated. This breakthrough suggests a reduced role of aerosol-cloud interactions in determining climate sensitivity.
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