Aerosols have a potentially large effect on climate, particularly through their interactions with clouds, but the magnitude of this effect is highly uncertain. Large volcanic eruptions produce sulfur dioxide, which in turn produces aerosols; these eruptions thus represent a natural experiment through which to quantify aerosol–cloud interactions. Here we show that the massive 2014–2015 fissure eruption in Holuhraun, Iceland, reduced the size of liquid cloud droplets—consistent with expectations—but had no discernible effect on other cloud properties. The reduction in droplet size led to cloud brightening and global-mean radiative forcing of around −0.2 watts per square metre for September to October 2014. Changes in cloud amount or cloud liquid water path, however, were undetectable, indicating that these indirect effects, and cloud systems in general, are well buffered against aerosol changes. This result will reduce uncertainties in future climate projections, because we are now able to reject results from climate models with an excessive liquid-water-path response.

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J.M.H., A.J., M.D., B.T.J., C.E.J., J.R.K. and F.M.O.C. were supported by the Joint UK BEIS/Defra Met Office Hadley Centre Climate Programme (GA01101). The National Center for Atmospheric Research is sponsored by the US National Science Foundation. S.B. and L.C. are respectively Research Fellow and Research Associate funded by FRS-FNRS. P.S. acknowledges support from the European Research Council (ERC) project ACCLAIM (grant agreement FP7-280025). J.M.H., F.F.M., D.G.P. and P.S. were part-funded by the UK Natural Environment Research Council project ACID-PRUF (NE/I020148/1). A.S. was funded by an Academic Research Fellowship from the University of Leeds and NERC urgency grant NE/M021130/1 (‘The source and longevity of sulphur in an Icelandic flood basalt eruption plume’). R.A. was supported by the NERC SMURPHS project NE/N006054/1. G.W.M. was funded by the National Centre for Atmospheric Science, one of the UK Natural Environment Research Council’s research centres. D.P.G. is funded by the School of Earth and Environment at the University of Leeds. G.W.M. and S.D. acknowledge additional EU funding from the ERC under the FP7 consortium project MACC-II (grant agreement 283576) and Horizon 2020 project MACC-III (grant agreement 633080). G.W.M., K.S.C. and D.G. were also supported via the Leeds-Met Office Academic Partnership (ASCI project). The work done with CAM5-Oslo is supported by the Research Council of Norway through the EVA project (grant 229771), NOTUR project nn2345k and NorStore project ns2345k. We thank the following researchers who have contributed to the development version of CAM5-Oslo used in this study: K. Alterskjær, A. Grini, M. Hummel, T. Iversen, A. Kirkevåg, D. Olivié, M. Schulz and Ø. Seland. The AQUA/MODIS MYD08 L3 Global 1 Deg. data set was acquired from the Level-1 and Atmosphere Archive and Distribution System (LAADS) Distributed Active Archive Center (DAAC), located in the Goddard Space Flight Center in Greenbelt, Maryland (https://ladsweb.nascom.nasa.gov/). This work is dedicated to the memory of co-author Jón Egill Kristjánsson who died in a climbing accident in Norway.

Author information

Author notes

    • Daniel G. Partridge

    Present address: College of Engineering, Mathematics, and Physical Sciences, University of Exeter, Exeter, UK.

    • Jón Egill Kristjánsson



  1. College of Engineering, Mathematics, and Physical Sciences, University of Exeter, Exeter, UK

    • Florent F. Malavelle
    •  & Jim M. Haywood
  2. Met Office Hadley Centre, Exeter, UK

    • Jim M. Haywood
    • , Andy Jones
    • , Mohit Dalvi
    • , Adrian A. Hill
    • , Ben T. Johnson
    • , Colin E. Johnson
    • , Jeff R. Knight
    •  & Fiona M. O’Connor
  3. National Center for Atmospheric Research, Boulder, Colorado, USA

    • Andrew Gettelman
  4. Chimie Quantique et Photophysique CP160/09, Université Libre de Bruxelles (ULB), Bruxelles, Belgium

    • Lieven Clarisse
    •  & Sophie Bauduin
  5. Department of Meteorology, University of Reading, Reading, UK

    • Richard P. Allan
    •  & Nicolas Bellouin
  6. National Centre for Earth Observation, University of Reading, Reading, UK

    • Richard P. Allan
  7. Department of Geosciences, University of Oslo, Oslo, Norway

    • Inger Helene H. Karset
    •  & Jón Egill Kristjánsson
  8. Earth Sciences Division, NASA GSFC, Greenbelt, Maryland, USA

    • Lazaros Oreopoulos
    • , Nayeong Cho
    • , Dongmin Lee
    •  & Steven Platnick
  9. USRA, Columbia, Maryland, USA

    • Nayeong Cho
  10. Morgan State University, Baltimore, Maryland, USA

    • Dongmin Lee
  11. Laboratoire de Météorologie Dynamique, IPSL, UPMC/CNRS, Jussieu, France

    • Olivier Boucher
  12. School of Earth and Environment, University of Leeds, Leeds, UK

    • Daniel P. Grosvenor
    • , Ken S. Carslaw
    • , Sandip Dhomse
    • , Graham W. Mann
    •  & Anja Schmidt
  13. National Centre for Atmospheric Science, University of Leeds, Leeds, UK

    • Graham W. Mann
  14. School of Earth and Environmental Sciences, University of Manchester, Manchester, UK

    • Hugh Coe
    •  & Margaret E. Hartley
  15. Department of Environmental Science and Analytical Chemistry, University of Stockholm, Stockholm, Sweden

    • Daniel G. Partridge
  16. Bert Bolin Centre for Climate Research, University of Stockholm, Stockholm, Sweden

    • Daniel G. Partridge
  17. Atmospheric, Oceanic and Planetary Physics, Department of Physics, University of Oxford, Oxford, UK

    • Daniel G. Partridge
    •  & Philip Stier
  18. Center for International Climate and Environmental Research, Oslo, Norway

    • Gunnar Myhre
  19. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA

    • Graeme L. Stephens
    •  & Hanii Takahashi
  20. Joint Institute for Regional Earth System Science and Engineering, University of California, Los Angeles, California, USA

    • Hanii Takahashi
  21. Faculty of Earth Sciences, University of Iceland, Reykjavik, Iceland

    • Thorvaldur Thordarson


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F.F.M. (text, processing and analysis of the satellite data and the model results), J.M.H. (text, analysis of the satellite data and the model results, radiative transfer calculations), A.J., A.G., I.H.H.K. and J.E.K. (model runs), R.A. (processing of the CERES data and contribution to the text), L.C. and S.B. (processing of the IASI data and contribution to the text), L.O., N.C. and D.L. (MODIS cloud regimes), D.P.G. (estimate of CDNC from MODIS data), T.T. and M.E.H. (provided emission estimates for the 2014–2015 eruption at Holuhraun), A.J., N.B., O.B., K.S.C., S.D., G.W.M., A.S., H.C., M.D., A.A.H., B.T.J., C.E.J., F.M.O.C., D.G.P. and P.S. (contribution to the development of UKCA), and G.M., S.P., G.L.S., H.T. and J.R.K. (discussion contributing to text and/or help with the MODIS data).

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Florent F. Malavelle.

Reviewer Information Nature thanks R. Allen, M. Schulz, B. Toon and the other anonymous reviewer(s) for their contribution to the peer review of this work.

Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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  1. 1.

    Supplementary Information

    This file contains Supplementary Methods, a Supplementary Discussion, Supplementary Tables, Supplementary Figures, Code Availability, Data availability and Supplementary References.


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