Constraining Uncertainty in Aerosol Direct Forcing

D. Watson-Parris*, N. Bellouin, L. T. Deaconu, N. A.J. Schutgens, M. Yoshioka, L. A. Regayre, K. J. Pringle, J. S. Johnson, C. J. Smith, K. S. Carslaw, P. Stier

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review


The uncertainty in present-day anthropogenic forcing is dominated by uncertainty in the strength of the contribution from aerosol. Much of the uncertainty in the direct aerosol forcing can be attributed to uncertainty in the anthropogenic fraction of aerosol in the present-day atmosphere, due to a lack of historical observations. Here, we present a robust relationship between total present-day aerosol optical depth and the anthropogenic contribution across three multimodel ensembles and a large single-model perturbed parameter ensemble. Using observations of aerosol optical depth, we determine a reduced likely range of the anthropogenic component and hence a reduced uncertainty in the direct forcing of aerosol.

Original languageEnglish
Article numbere2020GL087141
Pages (from-to)1-7
Number of pages7
JournalGeophysical Research Letters
Issue number9
Early online date9 Apr 2020
Publication statusPublished - 16 May 2020


DWP and PS acknowledge support from the NERC CLouds and Aerosol Radiative Impacts and Forcing: Year 2016 (CLARIFY-2016 and NE/L013746/1) project. PS additionally acknowledges support from the European Research Council (ERC) project constRaining the EffeCts of Aerosols on Precipitation (RECAP) under the European Union's Horizon 2020 research and innovation program with grant agreement no. 724602 and the Alexander von Humboldt Foundation. This research was funded by the Natural Environment Research Council (NERC) under grants NE/J024252/1 (GASSP), NE/I020059/1 (ACID-PRUF), and NE/P013406/1 (A-CURE); the National Centre for Atmospheric Science (DWP, LD, MY, KC, and PS); and the UK?China Research and Innovation Partnership Fund through the Met Office Climate Science for Service Partnership (CSSP) China as part of the Newton Fund (JJ, KC, LR). We made use of the N8 HPC facility funded from the N8 consortium and an Engineering and Physical Sciences Research Council grant to use ARCHER (EP/K000225/1) and the JASMIN facility (, last access: 4 September 2018) via the Centre for Environmental Data Analysis, funded by NERC and the UK Space Agency and delivered by the Science and Technology Facilities Council. We acknowledge the following additional funding: The Royal Society Wolfson Merit Award (KC), a doctoral training grant from the Natural Environment Research Council and a CASE studentship with the Met Office Hadley Centre (LR). CJS was supported by the European Union's Horizon 2020 research and innovation program under grant agreement no. 820829 (CONSTRAIN project). We acknowledge the World Climate Research Programme, which, through its Working Group on Coupled Modeling, coordinated and promoted CMIP6. We thank the climate modeling groups for producing and making available their model output, the Earth System Grid Federation (ESGF) for archiving the data and providing access, and the multiple funding agencies who support CMIP6 and ESGF. We also gratefully acknowledge the support of Amazon Web Services through an AWS Machine Learning Research Award. We thank Stephan Kinne and Dave Winker for useful discussions.

FundersFunder number
Earth System Grid FederationCMIP6
Met Office Hadley Centre
UK–China Research and Innovation Partnership Fund
Alexander von Humboldt-Stiftung
Amazon Web Services
Horizon 2020 Framework Programme
UK Space Agency
Engineering and Physical Sciences Research CouncilEP/K000225/1
Natural Environment Research CouncilNE/I020059/1, NE/J024252/1
Science and Technology Facilities Council
Royal Society
National Centre for Atmospheric Science
European Commission
European Research Council
Horizon 2020724602, 820829


    • aerosol
    • forcing


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