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

Status: final response (author comments only)

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
  • RC1: 'Comment on egusphere-2024-2547', Anonymous Referee #1, 25 Oct 2024
  • RC2: 'Comment on egusphere-2024-2547', Anonymous Referee #2, 29 Oct 2024
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.