London: On March 24, 536, the sky suddenly darkened across continental Europe as a thick dust cloud rolled in and stayed put for 18 months.

Historians such as Procopius record that the Sun shone as dimly as the Moon, causing summer frosts and snow showers and providing too little light to ripen crops and fruit. Three years later a similar dust veil blocked out sunlight for several months.

The natural catastrophes led to widespread famine and contributed to the devastation caused by the Great Justinian Plague, named after the Byzantine emperor at the time, which wiped out a third of Europeans.

The effects of the plague and famine, combined with decades of warfare, dealt a body blow to the Eastern Roman Empire from which it never really recovered - eventually losing territory in Africa, the Middle East and Europe.

Now scientists have determined that the cause was probably a series of North American volcanoes which shot huge amounts of sulphate and ash into the atmosphere, followed by further eruptions in the tropics.

New studies of ice cores and historical records by the British Antarctic Survey, Nottingham University and 17 other international institutions show that there was a huge volcanic eruption in 535 or early 536 in North America.

A second eruption occurred in 539.

The volcanic activity was ruinous for Mediterranean communities. Cassiodorus, a statesman in Italy, wrote that the country had “a winter without storms, spring without mildness, summer without heat”. It brought plummeting temperatures, drought and food shortages, and helped exacerbate the effects of the Justinian Plague of 541 to 543. The study’s author, Dr Michael Sigl, from the Desert Research Institute in Reno and the Paul Scherrer Institute in Switzerland, said: “Our new dating allowed us to clarify long-standing debates concerning the origin and consequences of the severe and global climate anomalies which began with the mystery cloud in AD 536 observed in the Mediterranean basin. “We found at least two large volcanic eruptions around this period. These cooler temperatures were caused by large amounts of volcanic sulphate particles injected into the upper atmosphere shielding the Earth’s surface from incoming solar radiation. “This provides notable environmental context to widespread famine and the great Justinian Plague.” The reconstruction, published in Nature, is derived from more than 20 ice cores in Greenland and Antarctica analysed for volcanic sulphate. Dr Francis Ludlow of the Yale Climate?&?Energy Institute said: “Ice core timescales had been misdated previously by five to 10 years leading to inconsistencies in the proposed timing of volcanic eruptions relative to documentary and tree-ring evidence recording climatic responses to the eruptions.”