by Lewis Loflin
Climate change has shaped human history in profound ways, often acting as a catalyst for societal shifts. As a Deist, I find the interplay between natural forces and historical events a compelling lens for understanding our past. From the 1st to 6th centuries, the Roman and Byzantine Empires faced climate-driven challenges—cooling periods, volcanic eruptions, and plagues—that led to crop failures, famines, and societal upheaval, ultimately paving the way for the rise of Islam.
The Western Roman Empire’s decline, from the end of Marcus Aurelius’ reign in 180 C.E. to its fall around 480 C.E., was exacerbated by climate change. A general cooling trend over five centuries disrupted agriculture across Europe, weakening populations already strained by political corruption and war. Plagues, such as the Antonine Plague (169–194 C.E.), which killed Marcus Aurelius, and another in 250–270 C.E., which claimed Emperor Claudius Gothicus, swept through the empire. Likely caused by smallpox, typhus, or measles, these epidemics thrived among a sick and vulnerable population, further destabilizing the region.
Climate change also drove Germanic tribes, including the Huns, into the Roman West. Cooling in Northern and Central Europe pushed these groups southward, seeking arable land and resources, adding pressure to an already faltering empire.
In 535–536 C.E., extreme weather events marked the most severe cooling episode in the Northern Hemisphere in 2,000 years, likely caused by massive volcanic eruptions—possibly Krakatoa (539 C.E.) and in El Salvador (534–535 C.E.). These eruptions created an atmospheric dust veil, blocking sunlight for 18 months starting in March 536 C.E. The resulting low temperatures caused drought, crop failures, and famines worldwide, setting the stage for the bubonic plague.
The plague, possibly carried from East Africa via ivory or grain ships from Egypt, spread rapidly along Roman trade routes, from Britain to the Black Sea. It devastated the Byzantine Roman and Persian Empires, killing millions in waves over decades. Historian Procopius of Caesarea, present at Justinian’s court in the 540s, wrote in his Persian War: “There was a pestilence by which the whole human race came near to being annihilated… It started among the Egyptians, then moved to Palestine and spread over the whole world… The mortality rose alarmingly, eventually reaching more than ten thousand each day.”
Emperor Justinian himself fell ill but survived, reigning for two more decades. The plague returned in 558 C.E., with Agathias noting it “swept the capital, destroying a vast number of people.”
The plague and famine spared central Arabia, weakening the Byzantine and Persian Empires while leaving the Arabian Peninsula relatively unscathed. By 632 C.E., Islam began its expansion, conquering much of the weakened empires. William Rosen, author of Justinian’s Flea: Plague, Empire, and the Birth of Europe, notes: “Before the 6th century was over, [the plague] had killed around 25 million people… Rome and Persia were so plague-weakened that the armies of Islam, formed in one of the only parts of either empire to remain plague-free, could conquer Mesopotamia, the Middle East, North Africa, Spain, and most of Asia Minor.”
The Medieval Warm Period (around 900 C.E.) brought recovery to Christian Europe, enabling agricultural expansion and the settlement of Vikings in Iceland and Greenland. This period also saw the Crusades (1095–1291), which halted Muslim expansion, notably at the Battle of Tours in 732 C.E.
A severe cold snap around 1300 C.E., following the Great Drought of 1276–1299, marked another climate downturn. The Vikings in Greenland survived until this period, when extreme cold and drought also ravaged Eastern North America, impacting early English colonists. The Black Death, peaking in Europe between 1348 and 1350, emerged during this cooling, killing 30% to 60% of Europe’s population. Originating in Central Asia, it spread via merchant ships, reducing the world’s population from 450 million to 350–375 million by 1400. Unlike earlier plagues, it reached deep into the Arabian Peninsula, recurring until the 19th century.
Posted September 6, 2009 by Lewis Loflin. For more on early Islam, see Chronology: Early Islam. For related climate impacts, see Paradise California Fire: Product of Nature, Human Error.
Insights from William Rosen’s Justinian’s Flea: Plague, Empire, and the Birth of Europe (www.justiniansflea.com) and Lester K. Little’s Plague and the End of Antiquity: The Pandemic of 541–750 (Cambridge University Press).
Acknowledgment: I’d like to thank Grok, an AI by xAI, for helping me draft and refine this article. The final edits and perspective are my own.
