The Dark Ages Were Caused By Two Enormous Volcanic Eruptions

“The sun gave forth its light without brightness.”

In 536 CE, the Byzantine historian Procopius wrote of a thick fog that suffocated the sun and plunged all of the Mediterranean into a year of cold and darkness. The phenomenon would signal the start of one of the greatest disease pandemics in history: the Plague of Justinian. In a single year, the outbreak killed an estimated 25 million citizens of the empire. It would be another two centuries until the plague finally succumbed, but by then, 50 million people had died in its wake.

"And it came about during this year that a most dread portent took place. For the sun gave forth its light without brightness, like the moon, during this whole year, and it seemed exceedingly like the sun in eclipse, for the beams it shed were not clear nor such as it is accustomed to shed," wrote Procopius. "And from the time when this thing happened men were free neither from war nor pestilence nor any other thing leading to death. And it was the time when Justinian was in the tenth year of his reign."

Now, a new study, published by a team of international climate scientists from the GEOMAR Helmholtz Centre for Ocean Research Kiel and the University of Oslo in the journal Climatic Change, offers exciting insights into what, exactly, pushed Procopius' world of Classical Antiquity into the literal Dark Ages.

Procopius wasn't the only scholar to note a chain of sudden catastrophic events in 536 CE and the years to follow. In addition to the plague, famine, and war that raged within the Mediterranean, historians around the globe were also documenting their own crises stemming from the scourge of unforeseen darkness.

In the Gaelic Irish Annals and the Annals of Inisfallen, an unknown author remarked of a "failure of bread" in 536 CE. That same year, a yellow dust that rained down like snow was seen in China, and a dense, dry fog descended upon the region between Europe and the Middle East. Further north, Old Norse literature chronicled the Fimbulvinter, or "notoriously long winter," which is evidenced by hordes of gold sacrificial offerings and abandoned settlements. And across the Pacific Ocean, an unprecedented drought kicked off the toppling of Mesoamerica's Teotihuacán, and brought down the mighty Moche civilization of Peru.

There were few empires that weren't touched by the cataclysmic climate event of 536 CE. Based on historical archives and artifacts, we know that some civilizations, such as the Frankish and Japanese, were deeply damaged by the phenomenon, while others, like the Anglo-Saxons, benefitted from its disruption. But what historians and archaeologists have never been able to conclusively figure out is what caused this reign of global demise.

Presently, a volcanic eruption of unrivaled size is the most popular theory for the ancient era of cold and darkness. Evidence corresponds to several volcanic explosions at this time, appearing in Central America, Indonesia, and North America. Ice cores from Greenland and the Antarctic show sulfate deposits resulting from an atmospheric acidic dust veil that have been dated to 536 CE. Dendrochronology—or tree ring dating—from tree samples around the globe show a decrease in growth rates during the years immediately following the eruption.

Simulated average temperature changes in 536 CE due to the stratospheric aerosol cloud resulting from an unknown volcanic eruption. Image: Matt Toohey/GEOMAR

The team of climate scientists responsible for the new study suggests that not one but two separate volcanic eruptions were responsible for the cooling event.

Using the same simulations employed to predict how current greenhouse gas emissions will contribute to modern climate change, the researchers discovered that separate explosions in 536 and 540 CE kicked off a double event that was "larger than that of any period in existing reconstructions of the last 1200 years."

The study's authors were able to confirm their "double peak" theory by matching their climate models to existing tree-ring evidence, as well as sulfate and carbon isotope data from ice core samples. According to their findings, each set of data exhibits mean temperature anomalies reaching -2 degrees Celsius at 536 CE and again four or five years later.

Not all of the data was an exact match, however. Some tree-ring and ice core reconstructions were a mismatch in regards to which years were the coldest and had the greatest impact on agricultural production. To account for differences in the magnitude of cold-spells during each of the two time periods, the scientists extended their atmospheric simulations to a length of 15 years, which resulted in similar climate-related impacts on agriculture. But the direct effects of each eruption, they found, were different around the world.

As for which supervolcano was the culprit, we still don't know for sure. The group of researchers has proposed the possibility of El Salvador's Ilopango, which is known to have erupted around 540 CE and at a latitude of 15 degrees north, matching the study's simulations.

What we are positive of, however, is that something at this time catalyzed mass panic, collapse, and depression all around the world. And it could very well happen again, but this time as a result of manmade greenhouse gas emissions. Will we be wise enough to learn from our ancestors? Right now, it seems unlikely.