Quantifying and Constraining Aerosol Forcing Uncertainty: From Single-Model to Multi-Model Perturbed Parameter Ensembles
Abstract
Changes in aerosols since the preindustrial era have altered the top-of-the-atmosphere radiation balance by directly scattering solar radiation and indirectly interacting with clouds, known as aerosol effective radiative forcing (ERFaer). ERFaer persistently remains one of the most uncertain components in global climate model simulations, due to the imperfect representations of aerosol and cloud properties and processes. Perturbed parameter ensembles (PPEs) are increasingly used to quantify these sources of uncertainty and to constrain models with observations.Here, we first present a single-model PPE using the ICON-A-HAM2.3 model, designed to identify key sources of ERFaer uncertainty. This PPE comprises 383 simulations for both preindustrial and present-day conditions, in which 42 parameters related to aerosol emissions, aerosol properties and processes, cloud microphysics, convection, and turbulence are perturbed simultaneously. Gaussian process emulators are trained on model outputs to enable efficient sampling of this high-dimensional parameter space. Our analysis focuses on uncertainty quantification and attribution for aerosol and cloud properties as well as ERFaer, along with comparisons against satellite observations from SPEXone/PACE and MODIS. Our results show a global mean ERFaer of −1.10 W m⁻² (5–95 percentile: −1.54 to −0.68 W m⁻²), with the overall uncertainty dominated by aerosol-related processes, particularly aerosol emissions.Building on this single-model framework, we further propose a Multi-Model PPE (MMPPE) initiative within the AeroCom Phase IV experiments. This multi-model approach allows us to simultaneously address structural and parametric uncertainties across models, providing a coordinated pathway toward reducing ERFaer uncertainty in current climate models. An overview of the MMPPE design and objectives will be presented.
Authors 21
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Space Research Organisation Netherlands
Affiliation as printed
SRON Space Research Organisation Netherlands, Leiden, The Netherlands
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Duncan Watson-Parris corresponding
Scripps Institution of Oceanography · University of California San Diego
Affiliation as printed
Scripps Institution of Oceanography and Halıcıoğlu Data Science Institute, University of California San Diego, La Jolla, CA, USA
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ETH Zurich · Institute for Atmospheric and Climate Science
Affiliation as printed
Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
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Space Research Organisation Netherlands
Affiliation as printed
SRON Space Research Organisation Netherlands, Leiden, The Netherlands
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Michael Schulz corresponding
Norwegian Meteorological Institute
Affiliation as printed
Norwegian Meteorological Institute, Oslo, Norway
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Leighton A. Regayre corresponding
Affiliation as printed
School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK
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Philip Stier corresponding
Affiliation as printed
Atmospheric Oceanic and Planetary Physics, Department of Physics, University of Oxford, Oxford, UK
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Johannes Quaas corresponding
Affiliation as printed
Leipzig Institute for Meteorology, Leipzig University, Leipzig, Germany
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Affiliation as printed
Department of Mathematics and Statistics, Faculty of Environment, Science and Economy, University of Exeter, EX4 4QF, Exeter, United Kingdom
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Space Research Organisation Netherlands
Affiliation as printed
SRON Space Research Organisation Netherlands, Leiden, The Netherlands
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Leibniz Institute for Tropospheric Research
Affiliation as printed
Modeling of Atmospheric Processes Department, Leibniz Institute for Tropospheric Research, Leipzig, Germany
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Athanasios Nenes corresponding
École Polytechnique Fédérale de Lausanne · Foundation for Research and Technology Hellas
Affiliation as printed
Institute of Chemical Engineering Sciences, Foundation for Research and Technology Hellas, Stadiou St, Platani GR26504 Patras, Greece
School of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Federale de Lausanne, Lausanne 1015, Switzerland
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Ulas Im corresponding
Affiliation as printed
Aarhus University, Roskilde, Denmark
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Affiliation as printed
Vrije Universiteit Amsterdam, Amsterdam, The Netherlands
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Space Research Organisation Netherlands
Affiliation as printed
SRON Space Research Organisation Netherlands, Leiden, The Netherlands
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Sylvaine Ferrachat corresponding
ETH Zurich · Institute for Atmospheric and Climate Science
Affiliation as printed
Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
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Ulrike Lohmann corresponding
ETH Zurich · Institute for Atmospheric and Climate Science
Affiliation as printed
Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
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Ina Tegen corresponding
Leibniz Institute for Tropospheric Research
Affiliation as printed
Modeling of Atmospheric Processes Department, Leibniz Institute for Tropospheric Research, Leipzig, Germany
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Alice Henkes corresponding
Affiliation as printed
Leipzig Institute for Meteorology, Leipzig University, Leipzig, Germany
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Space Research Organisation Netherlands
Affiliation as printed
SRON Space Research Organisation Netherlands, Leiden, The Netherlands
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