536: The Year Without a Summer and the Beginning of the Late Antique Little Ice Age

Illustration of the solar dimming phenomenon caused by volcanic aerosols in 536. — Illustration of the veil of dust and volcanic aerosols in the atmosphere, dimming the sun and plunging the northern hemisphere into prolonged twilight.
This "volcanic twilight," although lasting only a few years (about 3 years), initiated more than a century of climatic cooling.
Image source: astronoo.com (new window)

What was the Late Antique Little Ice Age and what event triggered it?

The year 536 CE marks a brutal climatic turning point. Chroniclers around the world describe a mysterious darkening of the Sun, whose light became "bluish" and whose heat no longer reached the Earth. This event, now identified as one of the largest volcanic eruptions of the last 2,000 years (likely in Iceland or North America), projected vast amounts of sulfur aerosols into the stratosphere, forming a global veil. It is considered the starting point of the Late Antique Little Ice Age (LALIA, ~536-660), a prolonged cooling period. The cascading consequences were dramatic: crop failures, massive famines, then the Plague of Justinian (541-542), weakening of the Byzantine Empire, and widespread political instability.

A catastrophic climatic event

The year 536 CE marks a brutal turning point in the climatic history of the northern hemisphere.
Chroniclers around the world, from Europe to China, describe a mysterious dimming (atmospheric phenomenon caused by the scattering of light by particles suspended in the air) of the sun, whose light appears "bluish" and whose heat no longer manages to warm the Earth.
That summer, snow fell in August in China, and crops were disastrous in Europe.
This singular event, now identified by scientists as one of the largest volcanic eruptions of the last 2000 years, is considered the starting point of the Late Antique Little Ice Age, a period of cooling that lasted more than a century (536–660).

Dendrochronology (science of dating and studying past climate variations through the analysis of tree rings (growth rings).) reveals in millennial trunks the indelible mark of the year 536: an exceptionally narrow ring, a climatic signature of a summer without warmth and a sky veiled by volcanic dust.

N.B.:
Research points to volcanoes located in the northern hemisphere (Iceland, North America, possibly Asia).
Aerosols injected into the stratosphere disperse mainly in the hemisphere of origin before slowly migrating to the other hemisphere.
The direct climatic impact (dimming, cooling) is therefore initially much stronger and more immediate in the hemisphere of origin.

Causes: Dust in the sky

Research in paleoclimatology (science that studies past climates, particularly through the analysis of ice cores) has identified the origin of this catastrophe.
Detailed analysis of ice cores from Greenland and Antarctica reveals an extremely high concentration of sulfates and volcanic ash precisely dating from 536.
Contrary to popular belief, it was not one, but probably two major super-eruptions, occurring a few years apart, that caused it.
The exact location of the volcano(es) remains debated, with likely candidates in Iceland or North America.
The explosion ejected immense quantities of sulfur aerosols (very fine solid or liquid particles suspended in the air) into the stratosphere (layer of the atmosphere located between 10 and 50 km altitude), forming a global veil that reflected part of the solar radiation back into space and caused global cooling.

N.B.:
Volcanic aerosols have a reflective power much greater than that of CO₂.
Their cooling effect is powerful but relatively short (1 to 3 years), unlike the warming induced by greenhouse gases, which builds up over centuries.

Cascading historical consequences

The impacts of this climatic shock were profound and lasting.

Agricultural crisis and famine: Cold and wet summers led to repeated poor harvests, causing massive famines that weakened populations.
Epidemics: A general weakening of the population, combined with migrations, created favorable conditions for the spread of diseases. The Plague of Justinian, which broke out around 541-542, found fertile ground in this context and caused millions of deaths in the Byzantine Empire and beyond.
Political and economic instability: The Eastern Roman (Byzantine) Empire was heavily affected, losing a crucial part of its workforce and tax resources. In Western Europe, this event exacerbated the difficulties of the post-Roman period.
Migrations and cultural transformations: In Central Asia, cooling may have disrupted steppe ecosystems, contributing to the movements of nomadic populations.

N.B.:
The Plague of Justinian (the first historically documented bubonic plague pandemic, 541-542) was not directly caused by climatic cooling.
However, famines and population displacements induced by poor harvests created ideal sanitary and social conditions for the emergence and explosive spread of the bacterium Yersinia pestis.
The climatic shock thus acted as a risk multiplier, transforming a localized epidemic into a continental demographic catastrophe.
The Plague of Justinian persisted in recurrent waves for nearly two centuries (until around 750).

Chronology and impacts of the Late Antique Little Ice Age
Period (CE)	Climatic/historical event	Key indicator (ice cores)	Main impact
536	Major volcanic eruption, "dimming of the sun".	Extreme peak of sulfates, sulfuric acid.	Sudden cooling, poor summer, start of poor harvests.
540 (approx.)	Probable second major eruption.	Second peak of sulfates in the cores.	Prolongation and worsening of cooling, absence of climatic recovery.
541-542	Emergence of the Plague of Justinian.	No direct signal, but established context.	Massive demographic decimation, weakening of the Byzantine Empire.
536 - 660 (approx.)	Prolonged cooling period (LALIA).	Sustained high levels of sulfates.	Decline in agricultural yields, recurrent famines, social restructuring.

Geopolitical consequences: Instability and conflicts

The 6th-century cooling is not the direct origin of conflicts, but an amplifying factor (factor that amplifies pre-existing vulnerabilities).
It exacerbates political tensions, territorial rivalries, and pre-existing social imbalances, transforming latent crises into geopolitical collapses for decades.

Disorganization of economic networks: Poor harvests and declining craft production disrupted Mediterranean trade circuits. The scarcity of agricultural surpluses reduced long-distance trade, weakened cities, and diminished the ability of states to levy taxes and finance military efforts.
Weakening of the Byzantine military: The demographic loss due to famines and plague significantly reduced the manpower and tax resources of the Byzantine Empire. This weakening limited its ability to resist Persian pressures on its eastern border and to contain Lombard expansion in Italy.
Increased migratory pressures: Climatic deterioration in Central Asia may have reduced steppe ecosystems, pushing nomadic peoples like the Avars westward. Their movements and conflicts with established populations created a shockwave across Eastern Europe and the Balkans.
Fragmentation and local wars: The scarcity of resources (food, productive lands) exacerbated tensions and power struggles within Germanic kingdoms and elsewhere, leading to local conflicts and chronic instability.

A precedent for modern climate change

The study of the Late Antique Little Ice Age offers a crucial perspective. It shows how quickly the Earth's climate system can shift following a major disruption, with consequences that far exceed the environmental realm to completely reshape human societies. In a world now facing rapid anthropogenic warming, this episode reminds us of the intrinsic vulnerability of civilizations to climatic upheavals. It also highlights the importance of natural archives, such as ice cores, for deciphering our past and better understanding the complex dynamics of the Earth system.

FAQ: Everything about the Late Antique Little Ice Age

How did scientists identify the 536 volcanic eruption?

Evidence comes mainly from the analysis of ice cores from Greenland and Antarctica. These cores reveal an extremely high peak of sulfates and volcanic ash dating precisely to 536. Dendrochronology (tree-ring study) confirms the impact: millennia-old trunks show an exceptionally narrow ring in 536, a signature of a summer without warmth and a sky veiled in dust. Contrary to popular belief, it was likely not one but two major super-eruptions (536 and ~540) that prolonged the cooling.

What is the link between the 536 eruption and the Plague of Justinian?

The cooling and darkening of 536-540 caused repeated crop failures and massive famines, severely weakening populations. This context of widespread malnutrition and population displacement created ideal sanitary and social conditions for the emergence and explosive spread of the bacterium Yersinia pestis. The climate shock did not directly cause the plague, but acted as a risk multiplier, turning a localized epidemic into a continent-wide demographic catastrophe. The Plague of Justinian broke out in 541-542 and persisted in recurrent waves until around 750.

What were the geopolitical consequences of this prolonged cooling?

The consequences were profound and lasting. The Byzantine Empire was heavily hit: the demographic loss due to famines and plague reduced its military manpower and fiscal resources, limiting its ability to resist Persian pressures and contain Lombard expansion in Italy. In Western Europe, the event exacerbated the difficulties of the post-Roman period. In Central Asia, the cooling disrupted steppe ecosystems, pushing nomadic peoples (like the Avars) westward, creating a shockwave across Eastern Europe and the Balkans. The scarcity of resources exacerbated tensions and power struggles, leading to chronic instability.