Scientists based their conclusions partly on observations of ice cores that were taken from glaciers in Greenland, and also from historical reports describing adverse weather conditions at the time.
It is known that volcanic eruptions can influence the climate, not least because they can block out sunlight due to the large amounts of smoke and ash that they blow into the atmosphere.
It’s thought that something similar happened in Europe in the early 1100s, when heavy rain and cold summers were observed.
And around that time, Mount Asama, a volcano in Japan, erupted, causing nearby rice paddies and fields to be covered with thick ash.
According to the Asahi Shimbun, researchers had previously thought that the adverse weather in Europe around that time was due to an Icelandic volcano eruption – the Hekla volcano in 1104.
But researchers analysed Greenland ice cores and found that increased amounts of volcanic sulphate did not seem to match up with this theory.
Volcanoes can eject vast amounts of smoke and ash into the air, which can affect the weather.
In addition, the researchers identified narrative sources which described what the weather was like around that time.
The report concludes: “We therefore posit that these anomalies may result from the cumulate climatic effects of several closely-spaced volcanic eruptions that occurred between 1108 and 1110 CE.”
The researchers found that many of the testimonies they discovered referred to crop failures and famines.
In 1109, for instance, the researchers discovered sources that revealed “persistent wet summer and autumn weather” in France, Belgium, and England.
A couple watch as Mt. Asama erupts in 2004.
This resulted in reduced crop yields in that year. They quoted one source from France – Orderic Vitalis, who reported in the Historia Ecclesiastica that excessive rain had “drowned the crops, the barrenness of the earth cried aloud, and the grave harvest was an almost total failure.”
The researchers noted that eruptions that took place in 1108 – 1110 “may have initiated the preconditions necessary for famine”.
The report states: “The sources of these eruptions remains unknown, but we propose that Mt. Asama, whose largest Holocene eruption occurred in August 1108 CE and is credibly documented by a contemporary Japanese observer, is a plausible contributor to the elevated sulphate in Greenland.
“Dendroclimatology and historical documentation both attest, moreover, to severe climatic anomalies following the proposed eruptions, likely providing the environmental preconditions for subsistence crises experienced in Western Europe between 1109 and 1111 CE.”
Researchers observed how sulphur deposits had fallen in Greenland ice.
However, the researchers did note that other causes for the famines were possible.
These included extreme weather that coincided with “destructive military tactics” such as ‘scorched earth tactics’ whereby forces destroy anything that might be useful to the enemy as they move.
The researchers also pointed to the possibility of ‘burdensome economic policies’ as a potential cause.
The report is titled ‘Climatic and societal impacts of a “forgotten” cluster of volcanic eruptions in 1108-1110 CE’ and is published in the journal Scientific Reports.
Scientists observed the effects that the volcano in Japan (not pictured) might have had thousands of miles away.
In addition to studying sulphur deposits in ice cores, the team also observed tree rings, which they could use to work out what temperatures were like hundreds of years ago, the Mail Online reports.
Sébastien Guillet, lead author of the research and a paleoclimatologist at the University of Geneva, told Vice last month that studying “old trees, ancient texts and ice-core data” made him feel like “a time traveller”.
“We suggested in the study that Mount Asama in Japan contributed to sulphur deposition in Greenland but this hypothesis still needs to be confirmed,” he added.