Stratospheric turbidity in the period 1600–1800 CE derived from lunar eclipse brightness and colour, and inferences for global volcanism

Abstract. During totality, the Moon is illuminated by sunlight refracted through Earth’s atmosphere, making its brightness and colour sensitive to atmospheric transparency. Stratospheric aerosols produced by major volcanic eruptions can substantially attenuate this light, potentially resulting in unusually dark lunar eclipses. Historical eclipse descriptions may therefore provide an independent source of information on past volcanic aerosol perturbations. Here, we compile a substantially expanded database of lunar eclipse observations between 1600 and 1800 CE, drawing on more than 1,300 records from nearly 400 observers, and systematically reconstruct eclipse brightness using the Danjon scale and derive corresponding estimates of aerosol optical depth. We compare these estimates with volcanic sulfate deposition from a bipolar ice-core array and stratospheric aerosol optical depth from the eVolv2k reconstruction. We test (i) whether unusually dark eclipses consistently followed major eruptions (>10 Tg SO₂), (ii) whether sulfur injection magnitude and eruption latitude influence eclipse darkness, and (iii) whether dark eclipses also occur without clear evidence of major eruptions.

Dark lunar eclipses were rare, but the darkest events closely followed major volcanic aerosol perturbations, notably in 1601, 1642, and 1696. More moderate perturbations in 1729 and 1739 were also associated with noticeable lunar darkening. However, not all major eruptions were followed by comparably dark eclipses, as illustrated by the relatively bright eclipse following the 1783 Laki eruption. This suggests that eclipse brightness depends not only on sulfur injection magnitude, but also on aerosol transport and spatial distribution, eruption latitude, injection altitude, the timing of the eclipse relative to peak aerosol loading, and eclipse geometry.

Although lunar eclipses do not provide an exhaustive record of past volcanic eruptions, they offer a complementary source of information on stratospheric aerosol perturbations. Combined with ice-core records, historical eclipse observations provide additional constraints for evaluating pre-instrumental reconstructions of stratospheric aerosol forcing.