Recent emphasis on climate science has impacted how we think about ancient civilizations.
Long-held theories about the collapse of ancient civilizations are starting to change.
Climate change wasn't the only factor in their collapse, but it played a large role.
Sign up for our newsletter to get the latest on the culture & business of sustainability — delivered weekly to your inbox.
Email address
Email address
Sign up
By clicking ‘Sign up’, you agree to receive marketing emails from Insider as well as other partner offers and accept our Terms of Service and Privacy Policy.
Advertisement

Coliseums, giant stone heads, abandoned gardens, and ancient signs of plumbing are all signs of a prosperous and intelligent ancient civilization.

So why leave it all behind?

For years, scientists have been trying to solve these mysteries and have developed varying theories.

However, with our current reckoning with a volatile climate, researchers are starting to apply the lens of climate change to the collapse of ancient civilizations.

Advertisement

Using carbon dating, isotopes in river or lake sediment, coring trees, and a variety of other techniques, scientists are starting to gain a better understanding of climate change as a contributing factor to ancient societal collapse.

Advertisement

Ancient Rome
A photo of the Roman Coliseum.
The Roman Coliseum is an enduring symbol of the great Roman Empire. NurPhoto/Getty Images
The Roman Empire has been on the mind lately. But for all its greatness, we can't help but wonder what happened to it.

The Roman Empire is lauded for its population and geographic size, with 75 million citizens at its peak and extending from northern Britain to the edges of the Sahara. But the more impressive a civilization, the more of a spectacle it becomes when it collapses.

The Roman Empire had everything going for it — interconnected cities, a universal currency, highways, libraries, and even a functioning sewage system.

A collection of things contributed to the collapse of the Roman Empire. However, researchers are now suggesting that climate change contributed to the collapse.

The Roman Empire benefitted from warm, wet, and stable weather that allowed abundant crops and economic success. When volcanic activity grew and led the world into the "Late Antique Little Ice Age," the Roman Empire began to lose its foothold.

The ice age led to low crop yields, famine, and poor health. It also made areas of the Roman Empire less hospitable and more open to invasion. Famine and poor health in the interconnected, colder areas of the Roman Empire also made it ripe for a plague to spread.

Changing weather introduced new diseases, and Rome dealt with three different plagues: smallpox, the Plague of Cyprian, and the bubonic plague.

Plagues, famine, and invasion all befell Rome as the weather shifted, contributing to its downfall.

Advertisement


Norse Civilization
A photo of a glacier in Greenland.
Hahn Glacier in the Johan Petersen Fjord. REDA&CO/ Getty Images
The Vikings first settled in Greenland after Erik Thorvaldsson, known as Erik the Red, was exiled from Iceland for manslaughter in around AD 985.

Soon, a group of Vikings lived in Greenland for about 465 years, from 985 to 1450. But suddenly, they disappeared, leaving behind their homes and communities, and in the 15th century, signs of Norse habitation disappeared from the geological record.

The newest leading theory is that climate change was a major contributing factor. A study by Marisa Borreggine, a doctoral candidate in the Department of Earth and Planetary Sciences at Harvard University, found that from 1100 to 1400, rising sea levels could have flooded Viking settlements by as much as 11 feet, affecting 78 square miles, a space 1.5 times the size of San Francisco.

The reason for the rise in sea levels was not a heating period that melted glaciers and caused the sea level to rise, but the Little Ice Age.

The Little Ice Age caused the Southern Greenland Ice Sheet, the nearest to Norse settlements, to grow and weigh down the land. As a result, the land was filled with water. The ice sheet even grew so large that its gravity pulled the ocean near it.

Though rising sea levels might not have been the sole reason for leaving Greenland, it was certainly a major factor when compounded with social unrest, scarcity of resources, and other political factors.

Advertisement

Angkor
A photo of the ancient capital Angkor Wat at sunset.
Angkor Wat, Cambodia, at sunset seen in a reflecting pond. Wolfgang Kaehler/Getty Images
Angkor was the capital of the Khmer Empire in Cambodia. It was labeled the "hydraulic city" for its utilization of local water sources to build a series of canals, reservoirs, dykes, and basins.

At its peak, an estimated 750,000 people lived there and covered 400 square miles. Research has begun pointing toward intense climate change as a significant contribution to the collapse of Angkor.

Because Angkor relied so heavily on water, researchers at Columbia University looked at the tree rings of evergreens in Cambodia to understand changes in precipitation.

They discovered that in the century before it collapsed, Angkor encountered two severe "megadroughts" lasting 20 to 30 years, each followed by intense monsoons. The combination of extreme dryness and intense rainfall caused catastrophic flooding.

"We're talking about dry spells the likes of which we've never seen in modern history," co-author of the study, Brendan M. Buckley, told Columbia Magazine. "And then, the skies open up and the rain won't stop."

Advertisement

Indus Valley
A photo of the foundation of carious brick buildings leading to a staircase and a larger building in the background.
The ruins of the archaeological site of Harappa, Indus Valley civilisation, 3rd millennium BC DEA / G. NIMATALLAH/ Getty Images
The Indus Valley civilization, one of the largest and most populous ancient civilizations, potentially fell due in part to climate change.

The Indus civilization developed 5,600 years ago and, at its peak, is believed to have held 10% of the world's population in the culture that expanded over 386,000 square miles, more extensive than ancient Egypt and Mesopotamia.

About a century ago, archeologists began finding evidence of old cities. Evidence suggests the cities were developed with grids and evidence of advanced plumbing, not seen again until Ancient Rome. Most notably, there was a startling lack of large buildings for royalty, which was typical of civilizations at the time.

With a civilization so populous, the mystery of why so many cities and buildings were abandoned seemingly overnight has gone unsolved for decades.

By reconstructing the landscapes of plains and rivers where these ancient civilizations once settled by analyzing satellite images of the area and collecting sediment samples.

Through these methods, the research teams could determine what crops were planted and when, how landscapes changed, and how that affected settlements.

Many of these cities were built on rivers fed by monsoon rains. As the climate changed and the monsoons became less frequent, crops and water sources were less reliable, facilitating a move east towards a reliable water source.

This shift devastated the Indus Civilizations, which relied on significant surplus years. As a result, larger cities collapsed as more minor, localized communities and economies started performing better.