Ancient Global Dimming Linked to Volcanic Eruption

March 19, 2008

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.

Scientists had suspected the dry fog was caused by a volcanic eruption or a comet strike, but searches had failed to uncover evidence for either catastrophe—until now.

"There is no need at the moment to invoke a large-scale extraterrestrial event as the cause, because the evidence is conclusive enough to say that it is certainly consistent with it being a large volcano," said study team member Keith Briffa of the University of East Anglia in the United Kingdom.

The discovery is detailed in a recent issue of the journal Geophysical Research Letters.

Global Ashfall

Tests show the Greenland sulphate molecules were deposited sometime between A.D. 533 and 536. This date correlates well with a sulphate peak found in an Antarctic ice core.

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, the scientists say.

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.

Continued on Next Page >>




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