When you think of the worst year in history, you might expect answers like 1349, when the Black Death ravaged Europe, or 1918, when the flu pandemic claimed tens of millions of lives. But according to Harvard historian Michael McCormick, the true low point came much earlier—in 536 AD. “It was the beginning of one of the worst times to be alive, if not the worst year,” says McCormick, who leads Harvard’s Initiative for the Science of the Human Past. His conclusion is based on a catastrophic event that blanketed parts of the world in darkness and triggered years of global suffering.

The Fog That Plunged the World into Darkness

Starting in early 536, a thick fog settled over large parts of Europe, the Middle East, and Asia. It dimmed the sun so drastically that it appeared more like the moon—pale and weak. Procopius, a Byzantine historian, documented the eerie phenomenon, writing, “The sun gave forth its light without brightness, like the moon.” For the next 18 months, sunlight was severely reduced. The impact was devastating. Temperatures in the Northern Hemisphere dropped by as much as 2.5°C (about 4.5°F), making the 530s one of the coldest decades in over 2,000 years. Crops failed across continents. In China, snow fell during summer. In Ireland, historical records note widespread famine from 536 to 539.

And then it got worse.

In 541, the Plague of Justinian broke out. This early form of bubonic plague swept across the Byzantine Empire and beyond, killing millions. Some regions experienced death rates as high as 50%. The disease further destabilized already struggling societies and may have contributed to the decline of the Eastern Roman Empire.

What Caused the Catastrophe? Scientists Look to Volcanoes

For centuries, historians acknowledged the hardships of the mid-sixth century, but the cause remained a mystery. That began to change when Michael McCormick teamed up with glaciologist Paul Mayewski and other researchers. By analyzing ice cores drilled from a glacier in Switzerland, they discovered evidence of a massive volcanic eruption in early 536. Ash from this eruption spread across the Northern Hemisphere, blocking sunlight and causing the drop in global temperatures. But that wasn’t the only eruption—two more followed in 540 and 547 AD, each compounding the climate crisis.

Their findings were supported by studies from the University of Bern, where Michael Sigl’s team matched volcanic eruptions with major cooling events over the last 2,500 years. According to their data, the volcanic eruption of 536—possibly in Iceland—was followed closely by another in 540, creating a double blow that triggered decades of hardship.

Ice Cores Tell the Story

Tree ring data had already shown unusual cold during this period, but ice cores offered even more precise evidence. When volcanoes erupt, they release particles like sulfur and bismuth into the upper atmosphere. These particles form a reflective layer that cools the planet. The Colle Gnifetti Glacier in the Swiss Alps held a particularly important clue. A 72-meter ice core extracted from the glacier preserved 2,000 years of atmospheric data, including pollution, volcanic activity, and climate patterns.

Using an advanced laser-scanning method, researchers could examine incredibly thin layers of ice—each representing a few days or weeks. This allowed them to build a highly detailed climate timeline.

Laura Hartman, a key researcher, found tiny particles of volcanic glass in the 536 layer. After comparing their composition to volcanic rocks around the world, she and volcanologist Andrei Kurbatov linked them to Iceland. Still, some experts believe more evidence is needed to rule out other possible locations, like North America.

Regardless of the eruption’s exact origin, its global consequences are clear. Volcanic ash darkened the skies, temperatures plummeted, and global food production collapsed. These cascading events triggered economic depression and societal breakdown, particularly in Europe.

Signs of Recovery—and History Repeating Itself

The good news is that humanity began to rebound. By 640 AD, ice cores show a rise in airborne lead particles, a byproduct of silver mining. This suggests that trade, mining, and industry were picking back up. By 660, a further increase in lead pollution indicates a growing demand for silver, possibly as it became the preferred currency. This shift likely points to the emergence of a new merchant class and the gradual return of economic stability.

But nature wasn’t done yet.

During the Black Death in the 14th century, ice cores once again showed a dramatic drop in lead pollution—evidence of another economic collapse tied to disease. Archaeologist Christopher Loveluck calls the merging of historical records with environmental data a “game changer” for understanding the deep relationship between natural disasters and the rise and fall of civilizations.

Final Thoughts

The year 536 AD might not be the most well-known disaster in history, but based on scientific and historical evidence, it was likely the worst year to be alive. The fog, the freezing temperatures, crop failures, famine, and the onset of plague created a perfect storm that nearly shattered entire civilizations. And it all began with a volcano.

Today, these findings aren’t just historical curiosities—they serve as sobering reminders of how vulnerable human civilization can be in the face of nature’s fury.