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 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 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.
Research in paleoclimatology 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 into the stratosphere, 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.
The impacts of this climatic shock were profound and lasting.
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).
| 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. |
The 6th-century cooling is not the direct origin of conflicts, but an amplifying factor.
It exacerbates political tensions, territorial rivalries, and pre-existing social imbalances, transforming latent crises into geopolitical collapses for decades.
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.
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