Strong constraints on aerosol-cloud interactions from volcanic eruptions
Reason for embargo
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.
JMH, AJ, MD, BTJ, CEJ, JRK and FMOC 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 U.S. National Science Foundation. SB and LC are respectively Research Fellow and Research Associate funded by F.R.S.-FNRS. PS acknowledges support from the European Research Council (ERC) project ACCLAIM (Grant Agreement FP7-280025). JMH, FFM, DGP and PS were part funded by the UK Natural Environment Research Council project ACID-PRUF (NE/I020148/1). AS was funded by an Academic Research Fellowship from the University of Leeds and a NERC urgency grant NE/M021130/1 (The source and longevity of sulphur in an Icelandic flood basalt eruption plume). RA was supported by the NERC SMURPHS project NE/N006054/1. GWM was funded by the National Centre for Atmospheric Science, one of the UK Natural Environment Research Council’s research centres. DPG is funded by the School of Earth and Environment at the University of Leeds. GWM and SD 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). GWM, KSC and DG were also supported through the financial support 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.
This is the author accepted manuscript. The final version is available from Springer Nature via the DOI in this record.
Vol. 546, pp. 485–491