Sulphur-rich volcanic eruptions triggered extreme hydrological events in Europe since AD 1850

Volcanic and anthropogenic aerosols, by reflecting solar radiation and acting as cloud condensation nuclei, play a key role in the global climate system. Given the contrasting microphysical and radiative effects of SO2 on rainfall amounts and intensities, the combined effects of these two factors are still poorly understood. Here, we show how concentrations of volcanic sulphate aerosols in the atmosphere, as derived from Greenland ice core records, are strictly correlated with dramatic variations of hydrological cycle in Europe. Specifically, since the second half of the 19th century, the intensity of extreme precipitations in Western Europe, and associated river flood events, changed significantly during the 12-24 months following sulphur-rich eruptions. During the same period, volcanic SO2 exerts divergent effects in central and Northern Europe, where river flow regimes are affected, in turn, by the substantial reduction of rainfall intensity and earlier occurrences of ice break-up events. We found that the high sensitivity of North Atlantic Sea Surface Temperature (SST) and North Atlantic Oscillation (NAO) to atmospheric SO2 concentrations reveals a complex mechanism of interaction between sulphur-rich eruptions and heat exchange between Ocean and atmosphere with substantial impacts on hydrological regime in Europe.