In an attempt to quantify how much volcanic eruptions contribute to climate variability, a team of researchers from the Desert Research Institute (DRI) in Nevada have examined reconstructions of nearly 300 individual eruptions throughout history.
Writing in the latest edition of the journal Nature, the study authors used a new reconstruction of the timing and associated radiative forcing of events dating as far back as the early Roman period and demonstrated that large eruptions in the tropics and high latitudes were “dominant drivers of climate variability,” explained lead investigator Dr. Michael Sigl.
Dr. Sigl, an assistant research professor with DRI and a postdoctoral fellow at the Paul Scherrer Institute in Switzerland, added that these volcanic eruptions were “responsible for numerous and widespread summer cooling extremes over the past 2,500 years” and that those cooler conditions were the result of “large amounts of volcanic sulfate particles injected into the upper atmosphere, shielding the Earth’s surface from incoming solar radiation.”
In fact, the research reveals that 15 out of the 16 coldest summers recorded between 500 BC and 1,000 AD came following large volcanic eruptions, with four of the coldest happening not long after the largest volcanic events ever recorded. Essentially, the authors found evidence that large eruptions were responsible for cold temperature extremes throughout recorded history.
Using new techniques to address dating inconsistencies
Dr. Sigl’s team set out to address inconsistencies in historical atmospheric data observed in ice cores and corresponding temperature variations found in climate proxies such as tree rings, both of which had made it difficult to gauge the actual impact of volcanic eruptions on climate.
Their new reconstruction method utilized more than 20 individual ice cores which were extracted from ice sheets in Greenland and Antarctica, analyzing them for volcanic sulfate with technology at DRI. This analysis provided an annual history of atmospheric sulfate levels throughout various periods of time, and additional measurements took place at other participating universities.
“We used a new method for producing the timescale,” explained co-author Dr. Mai Winstrup, a postdoctoral researcher at the University of Washington, Seattle. “Previously, this has been done by hand, but we used a statistical algorithm instead. Together with the state-of-the-art ice core chemistry measurements, this resulted in a more accurate dating of the ice cores.”
Sigl added that the research team, which included 24 scientists from 18 universities and research institutes in the US, UK, Switzerland, Germany, Denmark and Sweden, used a “multidisciplinary approach” that involved historians and scientists specializing in space, climate and geology. This was “key to the success of this project,” he said.
New evidence of volcanism’s past effect on the climate
The study authors said that they were able to identify new evidence, including signs of a cosmic ray event, in the ice cores and tree rings that allowed them to significantly improve the accuracy of the dating process. Ice-core timescales had previous been misdated by five to 10 years during the first millennium, they noted, throwing off the proposed timing of volcanic eruptions.
The revised chronology of the eruptions and the climatic responses to those events revealed that sustained volcanic cooling effects on climate have triggered crop failures and famines, the study authors explained. In addition, these events may have played a role in pandemics and the decline of society in communities that were based primarily on agriculture, they added.
Tropical volcanoes and large-scale eruptions in high latitude parts of the Northern Hemisphere, such as Iceland and North America, often resulted in severe and widespread summer cooling in this part of the world due to the injection of sulfate and ash into the high atmosphere. Similarly, these particles caused atmospheric dimming over Europe that was recorded by eyewitnesses.
Climatic impact was strongest and most persistent after clusters of two or more large eruptions, the researchers found. They also found that one of history’s most severe climate crises, which began with an 18-month dust veil observed in the Mediterranean region starting in March 536 was the result of a large eruption in the high-latitudes of the Northern Hemisphere.