London, March 12 : A new theory has suggested that an enormous volcanic eruption in the sixth century seems to have triggered catastrophic global cooling, which had perhaps caused famine, cultural conflict and plague across the planet.
According to a report in Nature News, the theory offers an explanation for why historical records from the period make references to dimmer skies and a cooler climate.
Scientists have been studying evidence of this cold snap for more than 20 years. Tree rings from this time, for example, show that growth was slowed down by cold weather. he cause of these climate changes has been controversial. Now, however, it seems a volcano was to blame.
Climate cooling is consistent with the idea that the atmosphere became shrouded in a haze of dust, as is known to happen after large volcanic eruptions.
For example, a dust veil, causing cooling and spectacular sunsets, appeared after the eruptions of Tambora in Indonesia in 1815, and of Mount Pinatubo in the Philippines in 1991.
"Any normal interpretation of the data would point to a volcanic origin," says Keith Briffa, a palaeoclimatologist at the University of East Anglia in the UK and an author of the new study.
Briffa and an international team of collaborators have found the characteristic fingerprint of a volcanic eruption in layers of ice in the Greenland and Antarctic ice sheets, narrowly dated to around 533-536 AD. They think that the eruption happened in 535 AD, and that its effects were felt in the Northern Hemisphere in the following year.
This fingerprint takes the form of sulphate ions, formed from the sulphur dioxide released by volcanoes.
The fact that a sulphate layer can be seen not only in the northern but also the southern polar region implies that the eruption probably happened close to the Equator, so that its dust was dispersed all over the Earth.
The researchers say that the amount of sulphate they found implies that the eruption was even bigger than that of Tambora, perhaps releasing as much as 40% more dust. his, according to Briffa, makes the event "the most severe volcanic cooling event in the Northern Hemisphere in the past 2,000 years".
But, some experts have suggested that its consequences were more dramatic than mere crop failure and overcast skies.
Around 541, a plague pandemic rampaged from southern Asia to Denmark, wreaking havoc in the Byzantine Empire and possibly killing about 40% of the inhabitants of its capital Constantinople.