Deep ice cores taken from Greenland and Antarctica suggest 15 of the 16 coldest summers recorded between 500 BCE and CE 1,000 followed large volcanic eruptions.
The findings could resolve earlier discrepancies between data taken from ice core samples and tree rings that made it difficult to link cooler temperatures to past eruptions.
Previous ice-core timelines were off by five to 10 years in the first millennium CE, with discrepancies beginning to accumulate from the mid-1,200s. This prevented scientists from connecting volcanic eruptions with many major human events such as famine and plague.
The new chronology of volcanic eruptions reveals that such eruptions had a significant and repeated impact on global climate.
“Previously, there seemed to be a big delay between the dating of eruptions and big dips in tree-ring growth, so that researchers were forced to infer that either the eruptions didn’t actually impact climate, or that there must have been an error in the dating of tree-ring records,” says Francis Ludlow, a postdoctoral fellow at the Yale Climate and Energy Institute and coauthor of the study published in Nature.
Volcanic dust in Babylon
“We also show in the paper that a lot of quite dramatic accounts in ancient records of weakened or discolored sunlight from ancient Babylon to China now match the dates of big eruptions, so that these historical records are really recording high-altitude volcanic sulfuric aerosols and dust,” Ludlow says.
The work included identifying, translating, and interpreting cryptic human observations from China, Babylon, and Europe from as early as 255 BCE, a year in which an observer in Babylon noted that the disk of the sun resembled that of the moon, indicating the presence of high altitude volcanic dust and sulfate.
Ludlow says the new timeline helps resolve the origin of one of the most dramatic climatic downturns in recent human history: A period of unusually cold summers from CE 536-550 in the Northern Hemisphere that likely contributed to crop failures, famines, and plague.
“Before the new chronology, there were no eruptions that could have convincingly caused such a prolonged period of climatic and social disturbance,” Ludlow says, “but with the new dating we can now identify a major eruption in the high latitudes of the Northern Hemisphere in 536, followed by another huge eruption in the tropics around c. 540. It was this double-whammy that led to such severe and prolonged impacts.”
The National Science Foundation’s Polar Program funded the research, with further contributions from funding agencies and institutions in the US, Belgium, Canada, China, Denmark, France, Germany, Iceland, Japan, Korea, the Netherlands, Sweden, Switzerland, and the United Kingdom.
Source: Yale University