Cleopatra reportedly wouldn’t have seen ash clouds darken the sky from her throne in Alexandria, but the effects of an Alaskan volcano eruption spread to Egypt and the rest of the ancient world in 43 Before our era.
We are part of an interdisciplinary research team detailing the fingerprints of this eruption, which triggered a series of global climate changes during the first century BCE, one of the most critical periods of political transition in the world. history of western civilization.
Our work reveals how a single event occurring in a specific location can trigger a powerful cascade of change that can ripple across continents and seas – affecting not only plants and animals, but also social, political and economic dynamics. human societies.
An eruption 10,000 kilometers from Alexandria
In one of the most remote places on Earth, the Aleutian Island chain in the northern Pacific Ocean, in the winter of 43 BCE, Mount Okmok erupted. It was the largest eruption in the Northern Hemisphere in the past 2,500 years. It produced a sudden and massive drop in global temperatures that persisted for a decade.
Tree-ring records from California’s White Mountains mark the decade between 43 and 33 BCE as the second coldest in the Northern Hemisphere in human history. Italy suffered very cold summers which disrupted agriculture and military campaigns.
And in Egypt, the Nile has not been flooded for several years in a row.
When local people speak of the Nile today, they put their fists to their hearts, indicating the incalculable importance of its water for the existence of life in the desert.
Before the construction of Aswan and other dams in the 19th and 20th centuries, regular summer floods of the Nile made agriculture possible and civilization flourished along its banks. The flood was so severe that a large measuring device called a nilometer was built to track the height of the water along the river. Information was communicated across the region so planting could be synchronized with the timing and extent of the upcoming flood. In years of good floods, Egypt was the richest cereal land in the world.
In contrast, prolonged bad summer floods on the Nile have been associated with famines, riots, epidemics, reactive fiscal and trade policies, and spikes in food prices, often contemporaneous with large-scale organized revolts, according to our study. peer-reviewed research.
Unfortunately for Cleopatra, Mount Okmok erupted at a time when her regime was politically vulnerable.
In 48 BCE, the Roman general Pompey, seeking refuge and friendly welcome in Egypt after a disastrous battle against Julius Caesar, was assassinated within sight of Alexandria. Soon after, Cleopatra formed an alliance with Caesar. Cleopatra needed a Roman ally, and the royal treasury was extremely low. But then came the Ides of March in 44 BC. when Caesar was assassinated in front of the Roman Senate – a political shock for Rome and Egypt. Cleopatra, dreaming of reinvigorating the great Ptolemaic Empire, turned to another Roman general, Mark Antony.
But then the volcano in Alaska erupted.
Although little historical evidence survives from the 30s BC, recovery from starvation and disease would not have been quick. By 31 BCE, the Roman Empire had replaced both the Roman Republic and the Ptolemaic Kingdom of Cleopatra.
A new vision of the ancient world
In telling the story of the Hellenistic era, which took place between 320 and 30 BCE in the greater Mediterranean, historians have described the details of competitive state and city building, large-scale wars and cultural changes, as well as economic and technological achievements. . These historical accounts have almost always been based on the decisions of kings and high-level political actors.
A much lesser-known thread woven through many of these stories is the story of climate change. New research on the role of climate change during this period recasts some of the fundamental assumptions of this pivotal period and emerges as troubling and relevant to our modern world.
The work of scientists and historians rarely intersect, but as global temperatures continue to rise, questions about the interactions between society and climate become more pressing. In academia, more interdisciplinary teams are forming to study these interactions. Learning to integrate knowledge from different disciplines is vital for these collaborations.
Historians of ancient Egypt mostly rely on papyri, paper made from the papyrus plants that abounded along the banks of the Nile. This paper held the ink without blurring or smudging. The dry climate has allowed papyri to be preserved for millennia, providing incredibly detailed historical evidence in books, correspondence and legal documents. While historians on our team translated and analyzed ancient papyri, climatologists developed reconstructions and models of past climate change based on physical, chemical and biological evidence from ice and sediment cores, tree rings and mineral deposits in caves.
By aligning the timelines of change from different sources and disciplines, the research team linked the unique geochemical signature of the Okmok eruption to six specific dates. Arctic ice cores to the sudden cooling and drought of the 30s BC in the Mediterranean.
How volcanic eruptions change the climate
The Okmok eruption injected sulfur dioxide into the stratosphere, where winds are strong, causing aerosols to circle the planet. Like a giant umbrella, the aerosols reduced the amount of sunlight reaching the Earth’s surface. This led to cooler temperatures and a change in the typical location of high and low pressure systems. Because these pressure systems direct wind circulation and precipitation patterns, climatic conditions around the world have changed dramatically.
Impacts from sulfur dioxide aerosols have been seen in recent eruptions such as Mount Tambora in 1816 and Pinatubo in 1991, which lowered the Earth’s overall temperature by more than 1 degree Celsius for several weeks, even months at a time in some regions. The Tambora eruption in Indonesia led to what is known as the year without summerwhen frosts and lack of sunshine killed crops in New England and across Europe.
Climate models now confirm that, given the right initial conditions, large eruptions can even alter the position of the northern jet stream. Eruptions can also alter the seasonal migration of the Intertropical Convergence Zone, known as the ITCZ, the equatorial band of converging trade winds that determines the timing and duration of the rainy season along its southern edge in Africa. These cascading effects are probably the cause of the failures of the Nile floods in the time of Cleopatra.
Although the burning of coal, oil and methane gas is the cause of modern climate change – not a volcanic eruption – the effect is no less complicated or dangerous. Excess heat can be just as deadly to crops as cooling caused by reduced sunlight.
As climatologist Wally Broecker once said, “The climate is an angry beast, and we poke it with sticks.” The powerful impacts of a destabilized climate system have the potential to reshape our society. In our time of man-made climate change, the stories of history don’t seem so old.
Jennifer R. Marlon, Ph.D., is a research fellow at the Yale Program on Climate Change Communication, editor of this site.
Joseph Manning, Ph.D., is a historian at Yale University and principal investigator of the study Yale Nile Initiative.