by Medieval tomes that recorded when the moon’s color changed from blood red to black during lunar eclipses may help reveal vital clues about volcanic eruptions that may have triggered Europe’s Little Ice Age, a new study has found.
Volcanic eruptions can have major impacts on Earth by spewing ash, gases and dust that can block sunlight, triggering “volcanic winters”. For example, in 1815, Mount Tambora in Indonesia erupted in the largest volcanic eruption in recorded history, leading to the following year, 1816, being known as the year without a summer. The resulting weather anomalies led to June snowstorms in New England and crop failures around the world, killing more than 100,000 people from the resulting famines over the following decade, the city said. United States National Oceanic and Atmospheric Administration. noted (opens in a new tab).
The main ways scientists have studied the effects of volcanic eruptions on climate include estimating the acidity and amount of volcanic ash in polar ice core samples. They also inferred these changes from the amount of growth, or lack thereof, in the tree rings.
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However, the complex nature of atmospheric circulation has led to substantial uncertainty in the precise location, timing, and intensity of volcanic eruptions based on both polar ice core samples and ring data. of tree growth. It is therefore difficult to reliably estimate the climatic effects of these eruptions.
“I started looking for alternative tools, methodologies that could complement existing techniques,” lead study author Sébastien Guillet, a paleoclimatologist at the University of Geneva in Switzerland, told Space.com.
Guillet and his colleagues now suggest that medieval tomes around the world that have recorded details of lunar eclipses could help shed light on the climatic effects of volcanic eruptions.
“What I find particularly fascinating about these results is the intersection of ancient knowledge and modern science,” Guillet said. “It is remarkable to think that observations made by monks hundreds of years ago are still valid today and can inform our understanding of the impact of volcanic eruptions on climate.”
Scientists have studied the period of the High Middle Ages, ranging from 1100 to 1300 AD. Previous research has suggested that volcanism during this time may have helped trigger the Little Ice Age, a long period of cooling that saw the advance of European glaciers.
The researchers focused on historical accounts of total lunar eclipses – when the moon is entirely in the Earth’s shadow. Normally, during a total lunar eclipse, the moon takes on a reddish hue due to the way Earth’s atmosphere scatters sunlight onto the shadowed area. Blue and green light are scattered more than red light, leaving mostly red light to fall on the moon, Guillet explained.
However, volcanic eruptions can throw substantial amounts of ash and gas into the stratosphere, the layer of earth’s atmosphere ranging from approximately 6 miles to 11 miles (10 to 17 kilometers) at 30 miles (50 km) in elevation. These veils in the stratosphere can block sunlight, causing the moon to appear much darker during a total lunar eclipse. They would also have much stronger climate effects than volcanic emissions in the troposphere, the atmospheric layer below the stratosphere.
“Some of the darkest total lunar eclipses on record have followed large volcanic eruptions, such as the 1883 Krakatauthe eruptions of Agung in 1963, El Chichon in 1982 and Pinatubo in 1991,” Guillet said.
The scientists examined a total of 180 medieval documents from Europe, 10 from the Middle East and 199 from East Asia. These described 51, 7 and 61 total lunar eclipses respectively.
“The timing of lunar eclipses is very precise, making it an excellent point of reference for determining the time window during which a volcanic eruption occurred,” Guillet said.
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The Christian Records proved the most informative for the new study, providing data on the moon’s color and brightness for 36 eclipses. Researchers have suggested that the color of the lunar eclipse is imbued with great significance to Christian observers, possibly due to Christian texts such as John’s book of Revelation, in which a blood-red moon, as well as earthquakes and solar eclipsespredicted the end of the world.
If this research “was an exciting task, it also took a lot of time. We had to go through hundreds of texts written in languages that are no longer widely used”, remembers Guillet.
By examining the color and brightness of total lunar eclipses in ancient texts, researchers have been able to estimate the strength of the effect of volcanic eruptions on the stratosphere and therefore on global climate. The research team’s findings suggested that they could estimate the year and, in some cases, even the month of volcanic eruptions.
Scientists compared these historic findings with modern research on the duration between eruptions and the resulting effects on the atmosphere and climate. They linked five dark and two reddish lunar eclipses to major eruptions during the high medieval period. Dark lunar eclipses were observable for three to 20 months after an eruption.
The researchers then compared these estimates with tree-ring records in the northern hemisphere, in which unusually cold summers are linked to reduced wood formation. They found that five of these eruptions in AD 1110, 1172, 1229, 1258 and 1276 had a strong impact on the climate, while the remaining eruptions appeared to have had less of an effect.
This improved dating of major volcanic eruptions is “crucial to accurately quantify the impact of these eruptions on the climate,” Guillet said. For example, researchers can better understand how volcanic eruptions played a role in the start of the Little Ice Age compared to other factors, such as a period of low solar activity between 1280 and 1340. “This understanding will improve our understanding of the impact of volcanism on ancient societies,” Guillet noted.
Scientists have noted, however, that this new technique is not flawless. Only comments on the color of the moon are relevant, and accounts of partial eclipses cannot be used, since they essentially do not deal with the atmosphere. “It is important to combine this method with other records, such as ice cores,” Guillet said.
With a better understanding of the timing of these eruptions, “we can now focus on studying the impact of these eruptions on climate and societies,” Guillet said. “That’s the direction we’re going to take over the next few months.”
Additionally, “we intend to expand our research to other periods of high volcanic activity and see if there are any records of total lunar eclipses that could help us further refine the dating of these events.” , said Guillet. “But this is not an easy task, because as we go back in time, the number of historical documents providing information on the color of the eclipsed moon decreases.”
Scientists have detailed their findings (opens in a new tab) in April 6 in the journal Nature.
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