Ireland's Cold Winters Linked to Volcanic Eruptions: Ancient Texts Reveal Extreme Weather

It turns out that not only did Ireland have a volcanic past, but the eruptions may have been linked to cold weather. Medieval chronicles have given researchers clues that have helped them assess how volcanic eruptions affected the weather in Ireland 1,500 years ago.

Climate isn't nearly as well-catalogued in the past as it is today. Because of this, researchers often have to delve into historical texts as part of their efforts to reconstruct what events may have triggered environmental shifts in the past. Knowing this, the scientists critically assessed over 40,000 written entries in the "Irish Annals," which were manuscripts that were produced that determined the yearly chronology of feast days and included obituaries and notable political events. By comparing these entries to ice cores, the researchers were able to understand the climactic changes in Ireland over a 1,200-year period.

Ice cores catalogue climactic conditions in the past. Each year, the ice melts and then freezes again, forming layers that trap the gases and other particles in the atmosphere at the time. In this case, the ice cores revealed that up to 48 explosive eruptions occurred during the period that was being studied. Of these 48 events, 38 occurred around the time of 37 corresponding extreme cold events.

"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," said lead author, Francis Ludlow, in a news release. "In their severity, these events are quite rare for the country's mild maritime climate."

The findings have larger implications when it comes to how volcanoes affect our climate. Although the effect of big eruptions on the climate in summer is largely to cause cooling, during the winter, low-altitude eruptions in the tropics have instead been known to warm large parts of the northern hemisphere as they cause a strengthening of the westerly winds. This study, though, seems to point to the fact that some low-latitude eruptions correspond to extremely cold winters.

"The possibility that tropical eruptions may result in severe winter cooling for Ireland highlights the considerable complexity of the volcano-climate system in terms of the regional expression of the response of climate to volcanic disturbances," said Ludlow. "It is on the regional scale that we need to refine our understanding of this relationship as ultimately, it is on this scale that individuals and societies plan for extreme weather."

The findings are published in the journal Environmental Research Letters.