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Ancient Global Dimming Linked to Volcanic Eruption

From National Geographic News
Filipino farmers plow their rice fields as Indonesia's Mount Pinatubo spews ash following a major eruption in this photo taken July 8, 1991.

A year-long global cooling followed—but it was nothing compared to a massive cooling event in A.D. 536 that withered crops, sparked wars, and helped spread pestilence.

Now scientists have uncovered the first physical evidence that the ancient chill was due to a supervolcano eruption.

Photograph by Bullit Marquez/AP

A "dry fog" that muted the sun's rays in A.D. 536 and plunged half the world into a famine-inducing chill was triggered by the eruption of a supervolcano, a new study says. The cause of the sixth-century global dimming has long been a matter of debate, but a team of international researchers recently discovered acidic sulphate molecules, which are signs of an eruption, in Greenland ice. This is the first physical evidence for the A.D. 536 event, which according to ancient texts from Mesoamerica, Europe, and Asia brought on a cold darkness that withered crops, sparked wars, and helped spread pestilence. The team suspects the eruption occurred near the Equator, since its ash fell on both ends of the globe. The Greenland evidence is also consistent with tree-ring data from around the Northern Hemisphere that show reduced growth rates lasting more than a decade starting in A.D. 536. Curiously, the eruption's cooling effect did not extend to the southern hemisphere. Together, the tree-ring and acid evidence suggest the sixth-century eruption was even bigger than Indonesia's Mount Tambora eruption of 1815, which also dimmed the sun. According to written records, the dry fog lingered for just over a year — leaving an indelible mark on human history. Chinese historians recorded famine events and summer frosts for years after the event. If a similar volcanic eruption were to occur today, the effects could be just as devastating, experts say. The reduced sunlight and ashfall would affect agriculture worldwide, and the thick veil of dust and ash could cripple transportation and communication systems. "Most aircraft cannot fly in [volcanic] dust clouds. And these dust clouds have a large electrostatic potential that disrupts radio communication."

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