5 Civilizations Destroyed by Climate Change

Climate change might be getting a lot of headlines these days, but shifting global temperatures and weather patterns are nothing new. In fact, humans have been dealing with it for millennia. 

But our recent and firsthand understanding has prompted researchers to take a second look at some vanished civilizations to see what led to their downfall. Here are five that were destroyed—or had their decline drastically accelerated—by climate change. 

1. The Khmer Empire // Cambodia
2. The Mississippian Culture // United States
3. The Maya Civilization // Central America
4. The Indus Valley Civilization // Pakistan and India
5. The Akkadian Empire // Iraq

The Khmer Empire // Cambodia

Today, the ruins of the Angkor Wat temple complex in Cambodia are visited by over 2 million people a year. The temple, built in the early 12th century CE, served as the religious capital of the Khmer Empire. 

It was long believed the Khmer Empire collapsed after the neighboring Empire of Ayutthaya (modern-day Thailand) sacked its capital city in 1431. But scientists at the Greater Angkor Project, based at the University of Sydney, believe climate change is the real culprit.

Like much of the Khmer Empire, Angkor was a “hydraulic city” that relied on a network of reservoirs and channels to provide water for its 1 million people. Around 1300, global temperatures began to drop, kicking off the “Little Ice Age” that would last until the 1800s. Data from tree rings shows the Khmer Empire experienced drought alternating with punishing monsoons that filled its water infrastructure with silt. As the city’s population dwindled, repairing the irrigation system became impossible. 

Crop failures and water shortages led to social upheaval. Citizens converted to Buddhism, princes struggled for power, and the Ayutthaya Empire saw an opportunity for invasion. The sacking of the city in 1431 was just the nail in the coffin. 

The Mississippian Culture // United States

Cahokia—once the largest urban center of Mississipian culture—is a UNESCO World Heritage Site that’s protected by the state of Illinois as the Cahokia Mounds State Historic Site. It’s only a 15-minute drive from modern St. Louis.

The Mississippian culture flourished across the southeast and midwest United States from about 800 to 1500. Its people were known for building elaborate earthwork mounds, trade networks, and corn-based agriculture, which flourished during an unusually warm and wet period known as the Medieval Climate Anomaly. Cahokia grew from an agricultural village to an important political and religious center that was home to tens of thousands of people. 

But it all came crashing down at the beginning of the Little Ice Age. Core samples taken from nearby lakes show that rain shifted to the west, which disrupted the corn harvest and caused the Mississippi River to burst its banks. Cahokia flooded around 1150 CE.

In the period following the flood, archaeologists note an increase in defensive palisades and burned villages, indicating civil unrest. By the time Europeans arrived in the 1500s, all that was left of the once-great Mississipian culture’s settlements were ruins.

The Maya Civilization // Central America

Covering modern-day southeastern Mexico, Guatemala, and Belize, the Maya Civilization is known for its architecture, hieroglyphic writing, and astronomy charts. Although fragments survived into the modern period, the Maya suffered a political collapse around the year 900 CE. 

The Maya Civilization was composed of about 60 city-states, each ruled religiously and politically by a k’uhul ajaw. Depending on the region, the citizens cleared forests and used wetland or dry farming techniques; they also developed irrigation systems. The Maya had figured out a system that worked, allowing them to thrive throughout Central America. Until a major drought hit. 

Evidence for this change in climate comes from stalagmites in Yok Balum Cave in Belize. These cave formations need water to grow, and the more there is, the bigger they get; this means they provide remarkably accurate rainfall data for the past 2000 years. Based on data from the stalagmites, the Maya had prospered during an unusually wet period, and the civilization’s decline corresponds with one of the worst droughts in the region’s history. 

The Maya city-states didn’t get along at the best of the times, so the drought was a one-way ticket to war. Civilians fled and trade patterns shifted from land-based to sea-based to avoid the violence. Within a few generations, the once-great cities were all but forgotten.

The Indus Valley Civilization // Pakistan and India

The Harappan culture settled in the Indus River Valley of modern-day Pakistan and India starting around 3300 BCE, forming the Indus Valley Civilization. They thrived in the valley: Remarkable urban planning allowed the cities to take advantage of the river’s annual floods through a water management system while also creating drainage to keep the water away from urban centers. 

About 4200 years ago, one of the most significant climate events of the modern epoch—the 4.2-kiloyear event—hit the Indus Valley Civilization. A disruption in ocean currents weakened the monsoon rains so they no longer traveled far enough inland to flood the Indus River; the Indus Valley Civilization had no choice but to abandon their cities and move closer to the coast. Archaeologists believe this disrupted trade between Ancient Egypt and the Middle East.  

Evidence for the climatic event comes from a stalagmite found in India’s Caves of Meghalaya. The 4.2-kiloyear event was so disruptive that in 2018, the International Union of Geological Sciences officially recognized the current geologic age as the Meghalayan Age.  

The Akkadian Empire // Iraq

The Akkadians—considered by many to be the world’s first empire—ruled from 2300 to 2150 BCE. Centered on the lost city of Akkad, the civilization spanned across Mesopotamia, now part of modern-day Iraq [PDF]. 

The 4.2-kiloyear that devastated the Indus Valley Civilization hit the Akkadian Empire hard. Iraq experiences a northwesterly wind known as a shamal, which picks up sand from Jordan and Syria, often becoming a sandstorm. Winds can reach 40 miles per hour and dump piles of sand on roadways. For the Akkadian Empire, the increasingly cold and dry weather created longer and more frequent shamals. A marine sediment core from the Gulf of Omar indicates that a lot of silt was blowing into the area, which wasn’t good for growing food. Archeological studies show that cities on the northern plain were abandoned; clay tablets mention a mass migration to the south. 

But the Akkadians had their own explanation for their demise—divine retribution. They believed the gods were angered by their leader and sent the Gutian people to destroy them as punishment.  Like the Khmer Empire, though, the invaders weren’t the true cause of the destruction. The fate of the empire had already been decided by climate change. 

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