Repost: The Climate Crisis of 536 CE

Discussing a historical climate crisis and how it compares to the one we face today

A timeline from Science magazine of the 536 volcanic eruption and its effects. This article is basically an elaboration on this image.

In the year 536 CE, a massive volcanic eruption occurred, probably in Iceland¹. Vast quantities of volcanic ash were forced through the atmosphere, and the weather appears to have been just right to keep it circulating for 18 months as an aerosol-rich fog blocking sunlight. Average temperatures on the Earth of 536 then cooled by around 1.5 to 2.5 degrees Celsius (right about the range of warming we’re concerned about happening this century due to climate change!), kicking off the coldest decade in over 2300 years. This in turn spurred widespread famines; medieval historian Michael McCormick calls 536 “the worst year to be alive.”

The events of 536 and the following years are little known today, but they had incredibly profound effects on human civilization around the world:

• Procopius, a famed historian and advisor to Emperor Justinian I in what is now called the Byzantine Empire² famously wrote: “And it came about during this year [537] 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. And from the time when this thing happened men were free neither from war nor pestilence nor any other thing leading to death.”

• Cassiodorus, a Roman historian serving the post-Roman Ostrogothic kingdoms of Italy, wrote in 538: “The Sun, first of stars, seems to have lost his wonted light, and appears of a blue color…Whence can we look for harvest, since the months which should have been spent maturing the corn³ have been chilled by Boreas?” The following letters discuss famine relief efforts across Italy.

• The Irish Annals of Inisfallen record “a failure of bread from the years 536–539.”

• In Scandinavia, where a hodgepodge of migrating tribes were just starting to coalesce into the culture that would become known as the Vikings, archaeologists note a surge in buried gold hoards around this time, including many highly valuable and finely worked items that likely had religious significance. Although we may never know for sure, one paper speculates that this was an attempt to appease the gods to get normal weather back, and that memories of this dark time inspired the later myths of Fimbulwinter and Ragnarök.

  

  The Pyramid of the Moon, built by the Teotihuacan civilization, as it appears today

• The great Mesoamerican city of Teotihuacan (on a site which much later became the Aztecs’ Tenochtitlan, then Mexico City) collapsed right around this time, and it may be related (though again, we may never know for sure). Much of Teotihuacan was burned around 550 in what scholars consider to be an internal revolution, not foreign invasion, as only palaces and monuments were damaged with “normal” housing left untouched. There’s also a spike in the percentage of juvenile skeletons with malnutrition in the Teotihuacan area around this time, so it’s possible that volcano-induced global cooling led to famine which led to revolution.

• The year 537 is the traditional date for the probably-mythical Battle of Camlann, in which Mordred was said to have killed King Arthur somewhere in post-Roman Britain. Scholars disagree whether these people ever really existed (at the very least, their legend was wildly embellished in later medieval accounts) but it seems likely that there’s some kind of connection here. It’s possible that a memory of the great famine of the late 530s led later storytellers to conclude that such a dreadful event must have had an epic cause, like the death of a legendary king.

• Snow reportedly fell in China (which was then divided between several warring dynasties, in a centuries-long period of civil war after the end of the Han Dynasty and before the reunifying Sui and Tang Dynasties) in August in 537⁴, ruining the harvest. Cannibalism may have ensued.

• Climactic upheaval may have also contributed to the collapse of Peru’s Moche culture in the late 500s.

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Then, at least in Europe, everything got worse still. A second major volcanic eruption occurred in 540-541 (we’re not sure where), keeping temperatures unusually low. And then in 541, a horrifying new disease started to emerge in Justinian’s “Byzantine” Roman Empire, and rapidly became a deadly pandemic, known as the Plague of Justinian. This was the first recorded outbreak of Yersinia pestis, the bubonic plague bacterium, a later surge of which would cause the more famous Black Death of 1346-1353. Given the timing, it seems very possible (though there’s no proof) that a zoonosis event was sparked by the unseasonal cold, perhaps pushing rats closer to humans in some village somewhere where one of rats was carrying the first plague-bearing flea⁵.

Detail of a contemporary mosaic of Justinian I, emperor 527-565.

This plague had truly massive effects on the history of Europe and Asia: as many as 25-60% of the population of Europe might have died (historians disagree), and new flare-ups over the next few centuries killed millions more. Ice core samples reveal a decrease in atmospheric lead, indicating less mining and medieval industry which in turn likely reveals a prolonged economic downturn. Both Justinian and his geopolitical rival Khosrow I (also written as Khusrau or Chosroes), the Sassanian (Persian) emperor of the time were infected, but both survived.

This was likely a turning point in history. In 540, right before the plague, Justinian’s armies under the famed general Belisarius had retaken almost all of Italy (including Rome) from the Ostrogoths, having earlier reconquered much of North Africa. This was Justinian’s great renovatio imperii, or “Renewal of the Empire” project, intended to reconquer all the western territories of the Roman Empire that had been lost to Germanic “barbarians.” Success seemed completely plausible at the time, even likely. Constantinople was a rapidly growing city rivaling Rome at its height; the great Hagia Sophia had just been completed in 537 demonstrating the empire’s technological, economic, and religious might. And Belisarius was one of the outstanding generals of history. If Belisarius had held on to Italy, the famous “Fall of Rome” of 476 might have instead been remembered as just another period of crisis eventually overcome by the eternal Empire, and all of history would have been different.

But the plague weakened the Byzantines and led to a Gothic resurgence. Justinian would never consolidate control over Italy, and the (Western) Roman Empire would not rise again. In the wake of the famine and plague years, Europe plunged into a decades-long economic decline⁶ that was arguably the true beginning of the Middle Ages, with the remnants of the riches of classical antiquity fading into memory, then legend. And the aftereffects from all this likely made it possible for a new chapter of world history to begin: the weakening of the Byzantine and Sassanian empires from the plague probably helped made it possible for the rising power of Islam (founded by Muhammad in 621) to conquer much of the Middle East extremely rapidly in the 600s, creating what we now know as the Muslim world.

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So what can we learn from this?

From one perspective, it’s a straightforward warning from history of the kind of impact of a few degrees’ variance in global average temperatures can have, another impetus to deal with the variance that humanity’s greenhouse gas emissions are causing now. Even the brief period in the 530s of colder temperatures of a similar magnitude (i.e. 1.5-2.5°C colder than the norm, while we’re now at 1.1°C warmer and heading towards 1.5-2.5°C warmer in the next few decades) led to famines, mass deaths, civilizations collapsing, and major states being terminally weakened. Longer-term, it arguably contributed to hundreds of years of relative technological stagnation (at least in Europe). Using a highly oversimplified, completely unscientific lens, what we can say based on the events of the 530s and 540s is that a shift in global average temperatures of 1.5-2.5°C seems like A Really Quite Bad Thing To Have Happen.

On the other hand, this bout of global cooling was rapid-onset, with no time to prepare, and it happened in the 500s, when our species’ technology level was much lower. Justinian couldn’t look at satellite data or atmospheric chemistry results to get a sense of what was going on and what was likely to happen next. And the climate crisis of the Anthropocene is fundamentally within our control: we have a well-tested, rapidly advancing suite of clean energy-generation technologies that can replace climate-warming fossil fuels. Not to mention that the riches of technological modernity will help us adapt to and withstand the impacts of the climate crisis, and have already defeated some of the worst enemies of 530s humanity: we’ve had a vaccine against Yersinia pestis since 1897⁷. Even as climate change weirds the world’s weather, we’re not anywhere close to worldwide famine⁸. We already grow more than enough food to feed all humans-it’s just unevenly distributed. World hunger hit record lows in the 2010s, and there has never been a famine in a functioning democracy. Human civilization in the 2020s is way better equipped to survive in and even thrive during planetary turmoil than the human civilizations of the 530s.

On the other other hand, the climate crisis of the 530s was temporary: sunlight-reflecting ash settles out of the atmosphere in a few years, while heat-trapping carbon dioxide takes centuries. And there were no societal incentives to keep the 530s cooling going on even if the civilization at the time had had the power to do so; today we have to deal with well-funded incumbents lobbying to keep burning fossil fuels as long as possible. And there was a ceiling to how bad the 530s crisis could get: only so much ash had erupted and there was a maximum cooling effect it could have. Our warming is ongoing and continuous, and could get much worse if Anthropocene humanity makes really bad decisions and does things like keep burning coal through the 2100s. On the other other other hand, this is much less likely now that clean energy’s already growing rapidly: we’re on track to avoid the “worst of the worst” warming scenarios and we are making real, accelerating progress towards a clean energy-powered world.

The climate crisis of 536 is an absolutely fascinating story that helped shape the world we live in today, but it’s ultimately pretty dissimilar to the climate crisis we face in the 21st century. Perhaps the one inarguable point is climate is a major influence on human history, the development of our civilization, and the quality of life for humans on this planet. History is made up not only of rulers and battles, or even inventions and social movements, but of enormous, planet-shaping forces that were previously uncontrollable by humans. We now have the nigh-godlike power to shape such majestic entities; the composition of Earth’s atmosphere is in our species’ hands. It’s up to us what we’ll do with it.

1. The location of the volcano is still contested, but Iceland seems strongly probable. A 2018 study found particles of volcanic glass resembling those from Iceland volcanoes in a section of an ice core from the Swiss Alps that had been precisely dated to the spring of 536. Many of this newsletter's readers will be interested to learn that this study was led by renowned University of Maine Climate Change Institute glaciologist Dr. Paul Mayewski.

2. But was then just considered to still be the Roman Empire, with the capital moved to Constantinople (aka Byzantium).

3. Astute readers will note that the grain called “corn” in modern American English (Zea mays), more specifically “maize,” is native to the Americas and would not have been available in 530s Italy. However, the word “corn” was widely used in medieval Europe (and is still used in British English) to describe grain in general, from wheat to barley.

4. (Here’s an epic highly detailed StackExchange thread detailing the evidence and original sources for this).

5. Much of the information in this post without a link to a citation, including this cooling/plague hypothesis, is from The World, the magisterial new one-volume world history by Simon Sebag Montefiore.

6. As revealed by a decline in airborne lead in ice core samples.

7. Vaccines are so freaking awesome.

8. Although there are still some regional famines, mostly in very poor countries that are concurrently suffering some kind of violent upheaval, and climate change is making those worse. A new UN-supported report found that 43,000 excess deaths have been caused by drought in Somalia in 2022. Several failed rainy seasons in a row have greatly reduced crop yields, which, exacerbated by jihadist violence and the Ukraine war’s disruptions to global food shipments, has led to mass hunger.