Medieval monks could not have imagined, when describing a lunar eclipse , that they were writing down for future generations the impact of giant volcanic eruptions that occurred a few months ago and may have been among the causes of climate cooling that occurred at that time, according to a recent study.

The phenomenon of eclipse occurs when the moon falls on one line with the sun and the earth, and then the earth blocks the sun's light from it. The color of the astronomical body becomes reddish after losing its white luster.

In 1884, the French astronomer Camille Flammarion noticed that this red color had become darker. He spoke at the time of a possible link to the catastrophic eruption of the Krakatoa volcano in Indonesia the previous year, which spewed a huge amount of dust into the sky.

This link has been proven in recent decades, after major volcanic eruptions, including the Mount Pinatubo volcano in the Philippines in 1991, as explained to Agence France-Presse, researcher at the University of Geneva, Sebastien Guyet, the main author of the study, the results of which were published Wednesday in the journal Nature.

This expert in the sciences of climatology in antiquity, with a passion for the medieval era, knew that monks recorded celestial phenomena, including lunar eclipses. He notes that they were "particularly interested in its color, as they were based on the text of the Book of Revelation (about the end of the world), which talks about a blood-red moon."

“I was listening to Pink Floyd's album Dark Side of the Moon when I realized that the darkest lunar eclipses occurred about a year after major volcanic eruptions,” says Sebastien Guillet.

It has been proven that the twelfth and thirteenth centuries witnessed intense volcanic activity, with strong and close eruption incidents, including what happened at the level of the Samalas volcano in Indonesia in 1257.

These accidents left traces in the ice core, which contains volcanic particles that fell to the ground. But apart from what happened at Samalas, the chronology of these phenomena remains roughly.

However, a comprehensive reading of texts written by monks from the twelfth and thirteenth centuries, especially in Europe but also in the Middle East and Asia, made it possible to determine the time of these phenomena with greater accuracy.

Of a total of 51 lunar eclipses reported between the years 1100 and 1300, historians note at least five phenomena in which the astronomical body appeared abnormally dark.

A Japanese writer on December 2, 1229 described the scene saying, "There really was reason to be afraid."

Scientists compared the exact days of these events with information from the ice core, and compared these results with contemporary data. They deduced the history of volcanic eruptions that occurred a few months ago, which the monks were not aware of because they were so far away.

"This innovative approach succeeded in determining the date of the volcanic eruption, by year and sometimes by month," said Ann Lawrence Mathers, a historian at the University of Reading in Britain, in a commentary accompanying the study.

According to the paleoclimatologist, "the monks used to see the moon dark because it was obstructed by aerosols pushed into the stratosphere," at an altitude of more than 10 kilometers.

Only the most powerful volcanic eruptions throw to such great heights plumes of ash that turn into mist upon entering the atmosphere.

The researcher confirms that six giant eruptions occurred within two hundred years, which is exceptional.

Recent research has speculated that this intense volcanic activity may have contributed to the emergence of the "Little Ice Age", which affected part of the Northern Hemisphere from the 13th to the 19th centuries.

The volcanic aerosols reduced radiation from the sun and cooled temperatures on Earth.

"Strong tropical eruptions can cause a global cooling of about 1 degree Celsius in a few years," says geomorphologist Marcus Stoffel, one of the study's authors.

An analysis of tree rings, which are indicators of temperature changes, confirmed this cold wave, which particularly affected crops.

"The monks have not seen such a cold summer for a long time, with the impression that they constantly see clouds of mist," says Sebastien Guillet.

"However, there is no consensus yet among scientists" about the causes of this ice age, "and we still have a lot to learn from these eruptions," according to Guyet, who says, "It is better to start from their exact history to understand whether or not they had impact on climate and societies.