Volcanoes cooled the climate of Ireland dozens of times over 1,200 years, and these events have been tracked by researchers from several universities, using ancient Irish texts from monasteries. The evidence they uncovered show a clear link between volcanic eruptions and periods of extreme weather.
These ancient texts, comprising 40,000 records dating from A.D. 431 to 1649, were compared to evidence of volcanic eruptions collected from ice core samples as part of the Greenland Ice Sheet Project. Of the 48 volcanic eruptions during that time period, 38 of those events was associated with one of the 37 periods of cold temperatures recorded by the monks.
During the Dark Ages, Irish monks carefully recorded events like obituaries, feasts and periods of severe cold or heat in a series of papers called the Irish Annals. Researchers were able to confirm the dates of the texts from eclipses, which were also recorded.
"Our major result is that explosive volcanic eruptions are strongly, and persistently, implicated in the occurrence of cold weather events over this long timescale in Ireland. In their severity, these events are quite rare for the country's mild maritime climate," Francis Ludlow from Harvard University, lead author of the study, said.
When a volcano erupts, it releases sulfur dioxide, which can convert into an aerosol form of sulphate that is easily detected in layers of ice. These particles, when released to the air, reflect and block the Sun, cooling the Earth's surface. Ireland, which has a naturally moderate climate, was heavily affected by this process.
"When the weather is cold enough to allow you to walk over a lake in Ireland, it is pretty unusual. When it happened, it was remarkable enough to be recorded pretty consistently," Ludlow said.
Cooling from volcanoes in modern times has been widely noted, as was the case with 1991's explosion of Mount Pinatubo. Eruptions in the tropics often bring warmer air to Europe, causing warming there. But the record of the Irish Annals shows evidence that even these caused cooling in the past, including in 1600 from the eruption of a volcano in Peru. Researchers stated that this effect highlights the complexity of such systems.
The Irish Annals were compiled over a period of Irish history that stretch from about the fall of the Roman Empire to the Tudor conquest in the 17th century.
The journal Environmental Research Letters published the results of the findings.
