https://doi.org/10.5194/cp-2021-78 Preprint. Discussion started: 5 August 2021 c Author(s) 2021. CC BY 4.0 License. The blue suns of 1831: was the eruption of Ferdinandea, near Sicily, one of the largest volcanic climate forcing events of the nineteenth century? 5 Christopher Garrison1, Christopher Kilburn1, David Smart 1, Stephen Edwards 1. 1 UCL Hazard Centre, Department of Earth Sciences, University College London, Gower Street, London, WC1E 6BT, UK. Correspondence to: Christopher Garrison (
[email protected]) Abstract. One of the largest climate forcing eruptions of the nineteenth century was, until recently, 10 believed to have taken place at Babuyan Claro volcano, in the Philippines, in 1831. However, a recent investigation found no reliable evidence of such an eruption, suggesting that the 1831 eruption must have taken place elsewhere. A newly compiled dataset of reported observations of a blue, purple and green sun in August 1831 is here used to reconstruct the transport of a stratospheric aerosol plume from that eruption. The source of the aerosol plume is identified as the eruption of Ferdinandea, which took place 15 about 50 km off the south-west coast of Sicily (lat. 37.1o N., long. 12.7o E.), in July and August 1831. The modest magnitude of this eruption, assigned a Volcanic Explosivity Index (VEI) of 3, has commonly caused it to be discounted or overlooked when identifying the likely source of the stratospheric sulphate aerosol in 1831. It is proposed, however, that convective instability in the troposphere contributed to aerosol reaching the stratosphere and that the aerosol load was enhanced by addition of a sedimentary 20 sulphur component to the volcanic plume.