Lunar eclipses illuminate timing and climate impact of medieval volcanism

Explosive volcanism is a key contributor to climate variability on interannual to centennial timescales(1). Understanding the far-field societal impacts of eruption-forced climatic changes requires firm event chronologies and reliable estimates of both the burden and altitude (that is, tropospheric versus stratospheric) of volcanic sulfate aerosol(2,3). However, despite progress in ice-core dating, uncertainties remain in these key factors(4). This particularly hinders investigation of the role of large, temporally clustered eruptions during the High Medieval Period (HMP, 1100-1300ce), which have been implicated in the transition from the warm Medieval Climate Anomaly to the Little Ice Age(5). Here we shed new light on explosive volcanism during the HMP, drawing on analysis of contemporary reports of total lunar eclipses, from which we derive a time series of stratospheric turbidity. By combining this new record with aerosol model simulations and tree-ring-based climate proxies, we refine the estimated dates of five notable eruptions and associate each with stratospheric aerosol veils. Five further eruptions, including one responsible for high sulfur deposition over Greenland circa 1182ce, affected only the troposphere and had muted climatic consequences. Our findings offer support for further investigation of the decadal-scale to centennial-scale climate response to volcanic eruptions. Analysis of contemporary reports of total lunar eclipses, combined with aerosol model simulations and tree-ring-based climate proxies, allowed greater precision in dating of the occurrence of stratospheric volcanic eruptions during the High Medieval Period.

Automated summary

Explosive volcanism is an important factor in climate variability on interannual to centennial scales internationally. However, uncertainties remain in key factors such as event chronologies and estimates of volcanic sulfate aerosol. This study sheds new light on explosive volcanism during the High Medieval Period through analysis of lunar eclipses, aerosol model simulations, and tree-ring-based climate proxies. The findings refine the estimated dates of notable eruptions and provide support for further investigation of the climate response to volcanic eruptions.