If you ask historian Michael McCormick to name the worst year in human history, his answer isn’t what you might expect. It’s not 1349, when the Black Death wiped out half of Europe, nor 1918, when the flu pandemic killed tens of millions. Instead, he points to 536 AD, a year marked by an unprecedented global catastrophe. “It was the beginning of one of the worst periods to be alive, if not the worst year,” says McCormick, who leads Harvard University’s Initiative for the Science of the Human Past. A strange and persistent fog covered much of Europe, the Middle East, and parts of Asia, triggering widespread devastation.
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535: A Year of Darkness and Despair
For nearly a year and a half, a dense fog hung over vast regions, blocking sunlight and plunging the world into darkness. Byzantine historian Procopius described it, writing, “For the sun gave forth its light without brightness, like the moon, during the whole year.” The result was catastrophic. Temperatures in the Northern Hemisphere dropped by 1.5°C to 2.5°C, making the 530s one of the coldest decades in recorded history. China saw summer snowfall, crops failed across continents, and famine set in. Irish historical records document severe food shortages from 536 to 539.
Then, just when it seemed things couldn’t get worse, disease struck in 541 AD. The bubonic plague, known as the Plague of Justinian, killed millions across the empire, with estimates ranging from 25% to 50% mortality in heavily affected regions. Some historians believe this contributed to the empire’s decline.
Unraveling the Mystery: The Role of Volcanoes
For centuries, scholars recognized the mid-sixth century as a time of extreme hardship, but the cause of the mysterious climate disaster remained unknown. A breakthrough came when Michael McCormick and glaciologist Paul Mayewski led a research team to analyze ice cores from a Swiss glacier. Their findings revealed a likely culprit: a massive volcanic eruption in Iceland that spewed ash across the Northern Hemisphere in early 536 AD. This was followed by two additional eruptions in 540 and 547, worsening the already dire conditions. The repeated blows, combined with plague, sent Europe into an economic depression that lasted for over a century.
The ice core also offered a glimpse of recovery. By 640 AD, scientists noticed an increase in airborne lead, a byproduct of silver mining. This suggested that trade and industry had finally begun to bounce back.
Ice Cores and Climate Clues
The search for answers began in the 1990s when tree ring studies revealed that the years around 540 AD were exceptionally cold. More recent studies of polar ice cores from Greenland and Antarctica added another piece to the puzzle. When a volcano erupts, it ejects sulfur, bismuth, and other particles into the upper atmosphere, forming an aerosol layer that reflects sunlight and cools the planet.
In 2015, a research team led by Michael Sigl from the University of Bern confirmed that nearly every significant cold period over the past 2,500 years coincided with a volcanic eruption. Their data pinpointed a major eruption in late 535 or early 536, followed by another in 540, explaining the prolonged global cooling.
Building on these findings, Mayewski’s team examined an ice core taken from the Colle Gnifetti Glacier in the Swiss Alps. This 72-meter-long ice core preserved over 2,000 years of environmental history, including volcanic activity, dust storms, and industrial pollution. Using an advanced laser technique, researchers analyzed microscopic layers of ice—each representing mere days or weeks of snowfall—to create an incredibly detailed timeline.
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A Glimpse of Recovery—and Another Collapse
In the ice layers from 536 AD, researcher Laura Hartman discovered tiny volcanic glass particles. By analyzing their chemical composition, she and volcanologist Andrei Kurbatov traced them to volcanic rocks found in Iceland. This strongly suggests that an Icelandic volcano triggered the global cooling event. However, some scientists, including Michael Sigl, believe further evidence is needed to rule out other sources, such as a North American eruption.
Regardless of its exact origin, the eruption had a devastating impact. Winds carried volcanic ash across Europe and Asia, darkening the sky and triggering climate shifts. Scientists now aim to locate additional volcanic deposits in European and Icelandic lakes to better understand why this particular eruption was so catastrophic.
A century later, the ice core reveals signs of economic recovery
Around 640 AD, a spike in airborne lead pollution suggests silver mining had resumed, marking a turning point in trade and industry. By 660 AD, another lead increase suggests a shift toward silver as the dominant currency, signaling the rise of a merchant class.
But history repeated itself. During the Black Death from 1349 to 1353, lead pollution in ice cores disappeared, mirroring another economic collapse. Archaeologist Christopher Loveluck of the University of Nottingham calls this integration of high-resolution environmental and historical records a “game changer” in understanding how natural disasters have shaped human civilization.
