Researchers have compiled descriptions of lunar eclipses from medieval manuscripts across Europe, the Middle East and Asia to help unravel the effects of volcanic activity on the planet. Light from a total lunar eclipse is filtered through Earth’s atmosphere, and a decrease in brightness is indicative of more aerosol particles, which are linked to recent volcanic activity. Based on descriptions of the colour and brightness of hundreds of eclipses from between 1100 and 1300, researchers were able to determine which eruptions affected the planet’s climate; the more recent the eruption, the darker the eclipse. The data was combined with simulations of how aerosol particles behave in the atmosphere, modern satellite observations and climate data from historical tree ring records.
Large volcanic eruptions pump ash, sulphur dioxide and other gases high into the atmosphere, which can lead to cooling or warming depending on what is expelled and the height it reaches. While volcanic emissions account for less than 1% of the carbon dioxide released by human activity, sulphur dioxide can form a veil of aerosols that cools the earth’s surface. The new study is seen to help researchers understand the role of volcanic activity in the transition to the Little Ice Age, a period of global cooling experienced between the 16th and 19th century.
The Little Ice Age was triggered in part by volcanic eruptions, which made the atmosphere hazier and blocked some incoming sunlight. However, information about these historic eruptions is often sparse and contradictory, so researchers have had to rely on traces left behind in polar ice and tree rings. The use of medieval manuscripts to determine the timing of eruptions offers a different way to deepen understanding of past events, as eyewitness accounts through oral traditional knowledge are often overlooked in the study of volcanoes. Researchers warn that in the future, it may take a bigger eruption to darken the moon because the altitude of the stratosphere will have increased as a result of warming.