536 CE: The Year Without a Sun, and Why It Happened

In 536 a mysterious dust veil dimmed the sun for over a year, bringing summer frost, crop failures and a century of cold.

In 536 CE writers across the Mediterranean recorded a dim sun for over a year, with summer frost and crop failures. Ice cores now point to large volcanic eruptions as the cause.

In 536 CE, writers across the Mediterranean recorded that the sun had lost its strength. The Byzantine historian Procopius, then with the army in the west, wrote that "the sun gave forth its light without brightness, like the moon, during this whole year," and that from then on war, plague and death never left humankind. In Italy, the Roman official Cassiodorus described a bluish sun, a moon without its glow, summer without warmth and crops failing from cold.

Chinese and Irish chronicles also record dimmed skies, summer snow, frost and famine in these years. Tree rings from Europe, Siberia and elsewhere show some of the coldest summers of the last two thousand years in 536 and the years after. Irish annals, for example, record a failure of bread in 536 and again in 539.

The cause was long a mystery; comet impacts were suggested. Ice cores from Greenland and Antarctica now point to volcanic eruptions: a large eruption in early 536, likely in the Northern Hemisphere and possibly in Iceland, followed by others in 540 and 547. Their sulfate aerosols blocked sunlight, and the cooling lasted for decades in what researchers call the Late Antique Little Ice Age.

The aftermath was severe. The Plague of Justinian broke out in 541, and historians debate how much the cold and famine contributed to political upheavals across Eurasia. A 2018 article in Science popularized 536 as possibly "the worst year to be alive". The cold helps explain why records of the time speak of the sun and moon as signs of the end.