Overview of the Nephele Perturbed Parameter Ensemble for Aerosol‐Cloud Interactions in E3SMv3.
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| Title: | Overview of the Nephele Perturbed Parameter Ensemble for Aerosol‐Cloud Interactions in E3SMv3. |
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| Authors: | Nugent, J. M.1 (AUTHOR) jnugent2@uwyo.edu, Brown, H.1 (AUTHOR), Kirby, A.2 (AUTHOR), McCoy, D. T.1 (AUTHOR), Allen, G.2 (AUTHOR), Aerenson, T.1 (AUTHOR), Burrows, S. M.3 (AUTHOR), Caulton, D.1 (AUTHOR), Fan, J.4 (AUTHOR), Feng, Y.4 (AUTHOR), Gettelman, A.3 (AUTHOR), Griswold, J.5 (AUTHOR), Jones, D. B.1 (AUTHOR), Leung, L. R.3 (AUTHOR), Mahfouz, N.3 (AUTHOR), Mikkelsen, A.1 (AUTHOR), Mülmenstädt, J.3 (AUTHOR), Qian, Y.3 (AUTHOR), Shan, Y.4 (AUTHOR), Shpund, J.3,6 (AUTHOR) |
| Source: | Journal of Advances in Modeling Earth Systems. Feb2026, Vol. 18 Issue 2, p1-28. 28p. |
| Subject Terms: | *Atmospheric aerosols, *Climate sensitivity, *Radiative forcing, Atmospheric models, Cloud physics |
| Abstract: | Aerosol‐cloud interactions (aci) are the leading source of uncertainty in inferring climate sensitivity from the historical record. Earth system models (ESMs) struggle to represent aci because the processes responsible for these phenomena occur at much finer time and space scales than can be resolved by any ESM. Observational constraints provide key benchmarks to test ESMs, but cannot be used alone to fully understand aci processes except in very specific cases where causality is controlled; some degree of modeling is required to infer aci and estimate radiative forcing. Here, we generate and characterize a perturbed parameter ensemble (PPE) in version 3 of the Energy Exascale ESM (E3SMv3). We perturb 25 parameters that govern aci processes over 250 members and integrate the model over present‐day and preindustrial aerosol emissions. We find that the process representation in E3SMv3 is flexible and can generate global‐mean effective radiative forcings due to aci (ERFaci) ranging from −3.0 to +0.9 W m−2. The positive ERFaci values simulated by a portion of the PPE are implausible and result from parameter combinations that produce unrealistic top‐of‐atmosphere energy fluxes. While global‐mean cloud droplet number concentration always increases in response to anthropogenic aerosol, cloud liquid water path can both increase and decrease, suggesting that precipitation suppression is not the only aerosol‐cloud adjustment represented by E3SMv3. Analysis of which processes control liquid cloud adjustment in the PPE points toward stratiform precipitation processes and aerosol activation, which is consistent with many previous ESMs, as well as the new two‐moment convective cloud microphysics in E3SMv3. Plain Language Summary: The central goal of developing Earth system models (ESMs) is to predict the future state of the planet as emissions of greenhouse gases and aerosol continue to change the Earth's radiative balance. To understand how sensitive our planet is to perturbations in net energy flux, we need to understand the relative effect of changes in radiation due to aerosol and greenhouse gases. Most of our uncertainty regarding the radiative effect of aerosols stems from their interaction with clouds, which must be parameterized in ESMs because of the large scale difference between the global climate and cloud droplets and aerosols. Here, we create a perturbed parameter ensemble (PPE) in the Energy Exascale ESM version 3 (E3SMv3) to study how our formulation of parameterizations affects the representation of aerosol‐cloud interactions. We also discuss how the PPE provides a useful tool to interpret observed variability and infer aerosol‐cloud interactions from observations. The E3SMv3 parameterization structure can represent aerosol‐cloud interactions that span from a net warming to a net cooling effect due to anthropogenic aerosols. Key Points: A perturbed parameter ensemble (PPE) is developed in E3SMv3 to study aerosol‐cloud interactions and adjustmentsThe E3SMv3 parameterizations can simulate a wide range of radiative forcings and adjustment processes in response to anthropogenic aerosolComparing PPE behavior and parameter dependencies regionally and globally helps improve our understanding of aerosol‐cloud interactions [ABSTRACT FROM AUTHOR] |
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| Abstract: | Aerosol‐cloud interactions (aci) are the leading source of uncertainty in inferring climate sensitivity from the historical record. Earth system models (ESMs) struggle to represent aci because the processes responsible for these phenomena occur at much finer time and space scales than can be resolved by any ESM. Observational constraints provide key benchmarks to test ESMs, but cannot be used alone to fully understand aci processes except in very specific cases where causality is controlled; some degree of modeling is required to infer aci and estimate radiative forcing. Here, we generate and characterize a perturbed parameter ensemble (PPE) in version 3 of the Energy Exascale ESM (E3SMv3). We perturb 25 parameters that govern aci processes over 250 members and integrate the model over present‐day and preindustrial aerosol emissions. We find that the process representation in E3SMv3 is flexible and can generate global‐mean effective radiative forcings due to aci (ERFaci) ranging from −3.0 to +0.9 W m−2. The positive ERFaci values simulated by a portion of the PPE are implausible and result from parameter combinations that produce unrealistic top‐of‐atmosphere energy fluxes. While global‐mean cloud droplet number concentration always increases in response to anthropogenic aerosol, cloud liquid water path can both increase and decrease, suggesting that precipitation suppression is not the only aerosol‐cloud adjustment represented by E3SMv3. Analysis of which processes control liquid cloud adjustment in the PPE points toward stratiform precipitation processes and aerosol activation, which is consistent with many previous ESMs, as well as the new two‐moment convective cloud microphysics in E3SMv3. Plain Language Summary: The central goal of developing Earth system models (ESMs) is to predict the future state of the planet as emissions of greenhouse gases and aerosol continue to change the Earth's radiative balance. To understand how sensitive our planet is to perturbations in net energy flux, we need to understand the relative effect of changes in radiation due to aerosol and greenhouse gases. Most of our uncertainty regarding the radiative effect of aerosols stems from their interaction with clouds, which must be parameterized in ESMs because of the large scale difference between the global climate and cloud droplets and aerosols. Here, we create a perturbed parameter ensemble (PPE) in the Energy Exascale ESM version 3 (E3SMv3) to study how our formulation of parameterizations affects the representation of aerosol‐cloud interactions. We also discuss how the PPE provides a useful tool to interpret observed variability and infer aerosol‐cloud interactions from observations. The E3SMv3 parameterization structure can represent aerosol‐cloud interactions that span from a net warming to a net cooling effect due to anthropogenic aerosols. Key Points: A perturbed parameter ensemble (PPE) is developed in E3SMv3 to study aerosol‐cloud interactions and adjustmentsThe E3SMv3 parameterizations can simulate a wide range of radiative forcings and adjustment processes in response to anthropogenic aerosolComparing PPE behavior and parameter dependencies regionally and globally helps improve our understanding of aerosol‐cloud interactions [ABSTRACT FROM AUTHOR] |
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| ISSN: | 19422466 |
| DOI: | 10.1029/2025MS004989 |
