The Late Antique Little Ice Age: A Catastrophe Forgotten by History

Until 2016, historians and climate scientists were studying the sixth century and almost completely overlooking the most catastrophic climate event of the past 2,000 years. The Late Antique Little Ice Age was unknown to popular history, unknown to most historians, unknown to most climate scientists. Yet this climate crisis lasted 125 years, killed millions of people, triggered pandemics, caused widespread famine, and reshaped civilizations across Eurasia. It was obscured by history, mentioned in ancient chronicles but not recognized as a coherent climate event.

A historian named Michael McCormick called the year five hundred thirty-six "the beginning of one of the worst periods to be alive, if not the worst year." Yet for nearly 2,000 years, the reason for this catastrophe remained mysterious. People in Constantinople reported the sun dimming. Crops failed across multiple continents. Disease spread. Empires contracted. Peoples migrated. But the underlying mechanism remained unknown.

Then, in February 2016, a study published in Nature Geoscience by a team of researchers including Ulf Büntgen described, for the first time, a unified explanation. A cluster of three massive volcanic eruptions in 536, 540, and 547AD had injected aerosols into the stratosphere. These aerosols blocked sunlight. The blocking triggered an unprecedented, spatially synchronized cooling across most of the Northern Hemisphere. This cooling lasted until approximately 660AD. The researchers named this climate period the Late Antique Little Ice Age. Understanding this ice age requires understanding what triggered it, how severe it was, and what global consequences followed.

What Triggered the Late Antique Little Ice Age

The fundamental cause of the Late Antique Little Ice Age was a cluster of three massive volcanic eruptions occurring in 536, 540, and 547AD. These eruptions were separated by roughly four to seven years, but they were close enough together that their cooling effects reinforced each other, creating a sustained climate shock.

The eruption in 536 was particularly catastrophic. While the exact volcano remains debated, the eruption was massive. It injected enormous quantities of sulfate aerosols into the stratosphere, the high layer of atmosphere above the troposphere where most weather occurs. These tiny particles—sulfate aerosols—scattered and absorbed solar radiation. Sunlight that would normally reach Earth's surface was instead reflected back into space.

This process is similar to what happens when you place a thin veil over a window. The veil does not completely block light, but it reduces the intensity of light passing through. Similarly, the aerosol veil did not completely block sunlight, but it significantly reduced the amount reaching Earth's surface. The reduction in solar energy reaching Earth's surface caused cooling.

Scientists calculate that the volcanic eruption of 536 produced a global forcing of approximately negative 11.3 watts per square meter. This measurement quantifies how much energy the eruption removed from Earth's climate system. To put this in perspective, the total human-caused greenhouse gas emissions today amount to roughly 2 watts per square meter. The volcanic eruption of 536 had approximately five to six times more cooling forcing than all current human greenhouse gas warming.

The eruption in five forty reinforced this cooling. Another massive eruption injected more aerosols into the stratosphere, extending the aerosol veil and maintaining the cooling. The eruption in 547 provided a third round of aerosol injection. By the time these three eruptions had all occurred, the stratosphere was filled with an aerosol layer so thick that it substantially reduced solar radiation reaching Earth for decades.

Additionally, research suggests that solar activity was at a minimum during this same period. A solar minimum is a period when the sun naturally produces slightly less energy. This solar minimum coincided with and reinforced the volcanic cooling. Ocean and sea-ice feedbacks may have further sustained the cooling. As the ocean cooled, it absorbed less heat. As sea ice expanded, it reflected more sunlight. These feedback mechanisms could have sustained the cooling even as aerosol particles gradually settled out of the atmosphere.

How Much Temperature Actually Dropped

The cooling during the Late Antique Little Ice Age was severe. In Europe, summer temperatures dropped between 2-2.7°C below normal. In Fahrenheit, this represents a 4-6° drop. These figures might sound modest, but the consequence was catastrophic.

Consider that the entire difference between an ice age and a warm period like today is roughly 5 to 10°C. A global cooling of 2°C is enormous on planetary scales. For context, the global warming since the Industrial Revolution is approximately one point three degrees Celsius. The cooling of the Late Antique Little Ice Age was roughly 1.5-2 times greater than all modern global warming.

Moreover, the cooling was not evenly distributed. Summer cooling was particularly severe, while winter temperatures may not have dropped as dramatically. This meant that growing seasons were shortened. Spring frosts arrived later, but summer failed to warm sufficiently for crops to mature properly. Growing seasons that normally lasted 5 to 6 months were shortened to 3 to 4 months. This reduction in growing season length was devastating for agriculture.

The temperature drops persisted for approximately 125 years, from 536 to approximately 660AD. This was a sustained climate change spanning an entire century and a quarter. Generations lived their entire lives during this cooler climate.

Tree-ring chronologies from the Russian Altai Mountains and European Alps confirmed this cooling through direct evidence. Trees grow more or less depending on conditions. Warm years with sufficient moisture produce wide rings. Cold or dry years produce narrow rings. Scientists examined trees from both regions and found an unprecedented pattern of narrow rings during the Late Antique period, confirming the cooling across a vast geographical area.

The Global Consequences

The consequences of the Late Antique Little Ice Age cascaded across the entire world. The cooling triggered crop failures, which led to famine, which weakened populations, which created conditions for plague, which killed millions. Political and social upheaval followed.

The most immediate consequence was agricultural failure. With growing seasons shortened by cold temperatures, crop yields plummeted. Grain harvests across Europe, Asia, and the Mediterranean fell dramatically. Food supplies that had sustained empires disappeared. Livestock suffered from shortened grazing seasons and poor nutritional quality of vegetation. Herds declined, reducing population size and nutritional value to human societies.

This agricultural collapse created widespread famine. Written accounts from the period describe hunger, starvation, and desperation. In Constantinople, grain prices skyrocketed as supplies dwindled. In rural areas, entire communities faced starvation. Malnutrition weakened populations, making them vulnerable to disease.

The Plague of Justinian followed, breaking out between 541 and 543AD, only 5 to 7 years after the initial volcanic eruption. This plague, probably caused by the bacterium Yersinia pestis, the same bacterium that caused the Black Death 1,000 years later, spread from Asia and devastated populations across the Mediterranean world, the Byzantine Empire, and beyond. The plague killed millions. Estimates suggest that the Justinian plague eliminated as much as 50% of the Byzantine Empire's population. Entire cities were depopulated. The plague's spread was facilitated by malnutrition and weakened immunity resulting from famine. Cold, drier climate conditions created favorable conditions for rodent populations that served as plague reservoirs. Nomadic human migrations during the crisis may have accelerated plague transmission.

Beyond the direct deaths from plague, the social disruption was massive. The Byzantine Empire, once the mighty Eastern Roman Empire, was dramatically weakened. Its military capacity was reduced. Its economic productivity plummeted. The empire's holdings in North Africa and the Mediterranean fell to rival powers. The empire never recovered its former power.

The Sasanian Persian Empire, Rome's great rival, collapsed during this period. Competing theories attribute the collapse to multiple factors, but the climate crisis and resulting instability may have been contributing causes.

Populations in Flux

The climate crisis and resulting food shortages triggered massive human migration. Populations dependent on pastoralism—herding livestock as their primary subsistence—faced reduced pasture quality and herd size. Shortened growing seasons meant that pastoral routes and timing no longer matched environmental conditions. Pastoral movements that had functioned for centuries became untenable.

Nomadic peoples in Central Asia, particularly in the steppes north of the Black Sea, experienced disruption of their traditional pastoral lifestyles. Migrations toward more productive lands began in earnest in the 540-50 era. Turkic peoples expanded westward. The Avars appeared north of the Black Sea during this period, eventually expanding into Eastern Europe.

Slavic-speaking peoples migrated southward and westward into formerly Roman territory in the Balkans and Eastern Europe. These migrations, traditionally explained by military conquest or cultural expansion, may have been substantially driven by the climate crisis and resulting food shortages.

In Central Asia, migrations toward China intensified. Populations fleeing the steppe crises pushed toward the Chinese frontier, creating military pressures on the Chinese dynasties of the period. Political upheavals in China during this era may be partially explained by these climate-driven migrations.

Lombards migrated into Italy, eventually establishing the Lombard Kingdom. The timing of these migrations correlates with the climate crisis and agricultural collapse.

In some regions, populations abandoning marginal lands due to crop failure led to settlement abandonment and economic collapse. In northeastern Germany and other peripheral regions, this period saw significant depopulation.

The Crisis Spanned Continents

Perhaps most strikingly, the effects of the Late Antique Little Ice Age reached far beyond Europe and Asia. Evidence shows that even the Mayan civilization in Central America, thousands of miles from the initial volcanic eruptions, experienced the cooling and its consequences. Archaeological and paleoclimate evidence suggests that the Mayan cities experienced drought during this period, contributing to political upheaval and the decline of the Classic Maya civilization.

This demonstrates that volcanic forcing can have global atmospheric effects, even affecting civilizations on opposite sides of the world. The aerosol veil did not remain confined to Eurasia. Atmospheric circulation distributes aerosols globally.

Ancient Chronicles Describing the Crisis

Contemporary accounts from the period provide vivid descriptions of the crisis, though chroniclers did not understand the underlying climate mechanism. Byzantine historians reported that in May 536, Constantinople experienced darkened skies. The sun appeared as if it had lost its brightness. Observers described the phenomenon as if there was an eclipse, but one that lasted for months rather than hours.

The historian Procopius wrote accounts of the period describing hunger, disease, and economic collapse. However, Procopius and other chroniclers of the era did not connect these disasters to a single underlying cause. Instead, they described them as separate calamities. It took modern climate science and tree-ring analysis to reveal that all these disasters were consequences of a single climate event.

Irish chronicles documented the Plague of Mohill in Ireland, where plague devastated populations following the extreme weather of 535 to 536. The plague is commemorated in place names that survived to modern times. Evidence of plague is revealed by townland names like Tamlaght (plague burial ground) surrounding the monastery of Mohill.

Hidden History Revealed by Science

The Late Antique Little Ice Age remained largely unknown to modern history until 2016 because historians and climate scientists had not connected the dots. Historical records documented crop failures, plagues, migrations, and political upheaval, but the underlying climate mechanism was invisible in historical chronicles.

Tree-ring analysis provided the key to unlocking this hidden history. Trees respond to climate conditions with ring width. Analyzing tree rings from the Russian Altai and European Alps, researchers could reconstruct summer temperatures over the past 2,000 years with unprecedented precision. The tree-ring data revealed an unprecedented pattern: a cluster of cold years beginning in 536 and persisting until approximately 660.

The precision of tree-ring dating revealed the timing of the cooling precisely. The cooling began immediately after the eruption in 536, confirming that the eruption triggered the cooling. The magnitude of the cooling, as revealed by tree-ring width variations, demonstrated that this was the most severe cooling event of the past 2,000 years.

Only after this tree-ring evidence was published in 2016 did historians and climate scientists begin to recognize the Late Antique Little Ice Age as a coherent historical and climatic event. Researchers then connected the climate data to historical events—crop failures, plagues, migrations, and political upheavals—revealing the causal links between climate and history.

The Bottom Line

The Late Antique Little Ice Age was a climate crisis lasting 125 years, triggered by a cluster of three massive volcanic eruptions between 536 and 547AD. These eruptions injected sulfate aerosols into the stratosphere, blocking sunlight and reducing summer temperatures by 2-2.7°C across much of the Northern Hemisphere. Shortened growing seasons caused crop failures and widespread famine. Malnutrition weakened populations, and in 541, the Plague of Justinian emerged, killing millions and devastating the Byzantine Empire. Large-scale human migrations followed as pastoral peoples found their traditional lifestyles unsustainable and agricultural societies abandoned marginal lands. Empires collapsed or contracted. Entire civilizations experienced upheaval. Even the Mayan civilization in Central America, thousands of miles away, experienced drought and turmoil. This catastrophic climate event reshaped human history for over a century, yet remained largely unknown to modern history until climate science revealed it through tree-ring analysis. The Late Antique Little Ice Age demonstrates that climate change, whether triggered by volcanic eruptions or other causes, has profound consequences for human societies. Understanding this historical event illuminates both the power of natural climate forcing and the vulnerability of human civilization to climate shocks.

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