Isthmus volcano a suspect in big chill

European researchers are looking at Central American volcanoes as possible suspects in the mystery cloud that dimmed the light of the sun above the Mediterranean in the years 536 and 537.

They also are looking at volcanoes in Indonesia and North America, they said.

The report was a joint one from the University of Oslo and the GEOMAR Helmholtz Centre for Ocean Research in Kiel, Germany.

Contemporary chroniclers wrote about the mystery cloud, according to the report. Tree rings testify to poor growing conditions over the whole Northern Hemisphere. The years from 536 onward seem to have been overshadowed by an unusual natural phenomenon. Social crises including the first European plague pandemic beginning in 541, are associated with this phenomenon, it said.

Only recently have researchers found conclusive proof of a volcanic origin of the 536 solar dimming, based on traces of volcanic sulfur from two major eruptions newly dated to 536 and 540 in ice cores from Greenland and Antarctica, the report said.

An international team led by Matthew Toohey at the GEOMAR Helmholtz Centre and Kirstin Krüger of the University of Oslo have investigated the time period using the new ice core data, historical evidence and climate models. As they write in the international journal Climatic Change, the impact of the volcanic double event of 536/540 on Northern Hemisphere climate was stronger than any other documented or reconstructed event of the past 1,200 years, according to the report.

“One of the eruptions would have led to a significant cooling of the Earth’s surface. Two of them, so close in time, caused what is probably the coldest decade of the past 2000 years,” Toohey was quoted as saying.

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