As we grapple with climate change, it's important to remember that this isn't the first time climate change has threatened grand, seemingly unstoppable civilizations.
The Ancestral Puebloans, also known as the "Anasazi" by the Navajo, are one of the most famous examples of an ancient civilization that collapsed due to climate change. Once dominant across the Colorado Plateau in places like Chaco Canyon and Mesa Verde (pictured), the Ancestral Puebloans abandoned their distinctive homes sometime in the 12th and 13th centuries, and it's not completely understood why they left. There's evidence of warfare, human sacrifice and cannibalism, but many scientists speculate that devastating environmental changes caused by climate change are largely to blame.
According to NOAA's Paleoclimatology branch, the decline in the Mesa Verde and Chaco Canyon villages "coincided with a prolonged drought in the San Juan Basin between 1130 and 1180. Lack of rainfall combined with an overtaxed environment may have led to food shortages. Even the clever irrigation methods of the Chacoans could not overcome prolonged drought. Under these pressures Chaco and the outliers may have experienced a slow social disintegration. The people began to drift away."
Here are four more ancient civilizations that went the way of the dodo because of climate change. Their ecological circumstances may have been vastly different from the ones we face today, but their stories offer vital lessons for modern times.
Khmer Empire of ancient Cambodia
First established in the ninth century, Angkor Wat was once the world's largest pre-industrial urban center. As the pride and joy of the powerful Khmer Empire, the city was famous for its immense wealth, opulent legacy of art and architecture and sophisticated network of waterways and reservoirs or barays that were optimized for storing summer monsoon waters.
However, by the 15th century, the marvelous city had been laid to waste by ecological overexploitation and a devastating water crisis caused by severe climatic fluctuations.
As scientist Mary Beth Day tells LiveScience, "Angkor can be an example of how technology isn't always sufficient to prevent major collapse during times of severe instability. Angkor had a highly sophisticated water management infrastructure, but this technologic advantage was not enough to prevent its collapse in the face of extreme environmental conditions."
Norse Viking settlers of Greenland
While Christopher Columbus is often celebrated for being the first European to "discover" North America, it's now widely accepted that Norse Vikings were way ahead of him by more than 500 years. While these initial settlements on the southern tip of Greenland thrived for many years, they descended into decline starting around the 14th century.
Scientists and historians have come up with several theories that speculate on the possible causes for the decline, though the overarching catalyst was likely the result of climate change. The arrival of the Norse Vikings in Greenland coincided with the Medieval Warm Period, which lasted from about 800 to 1200 A.D. During this time, the usually frigid Greenland boasted a relatively mild climate that was easy to farm and live off. However, as the world descended into the "Little Ice Age" of the 14th and 15th centuries, the settlements began to fail. By the mid-1500s, all Norse settlements had been abandoned for warmer lands.
Indus Valley civilization of present day Pakistan
Also known as the Harappan Civilization, this Bronze Age society once boasted a population of more than 5 million and was notable for its highly detailed urban planning and water systems. Two major cities that belonged to this civilization — Mohenjo-daro (pictured) and Harappa — were first discovered and excavated in the 19th century.
What led to their ruinous state? Two centuries of relentless drought. Scientists came to this conclusion after studying the layers of lake sediment from an ancient lake known as Kotla Dahar. Scientific American explains the nitty gritty of the findings:
"Kotla Dahar is a closed basin, filled only by rain and runoff and without outlets. Thus precipitation and evaporation alone determine its water volume. During drought, oxygen-16, which is lighter than oxygen-18, evaporates faster, so that the remaining water in the lake and, consequently, the snails' shells, become enriched with oxygen-18. The team's reconstruction showed a spike in the relative amount of oxygen-18 between 4,200 and 4,000 years ago. This suggests that precipitation dramatically decreased during that time. Moreover, their data suggests that the regular summer monsoons stopped for some 200 years."
The decline coincides with similar droughts suffered by civilizations in Egypt and Greece around the same time.
Maya civilization of ancient Mexico
The classic Maya collapse of the 8th and 9th centuries has captivated researchers for years. Although scholars are quick to point out that the Mayan civilization didn't technically "collapse," there's a great deal of mystery shrouding the abandonment of the Mayans' grand pyramids, palaces and observatories.
There are numerous theories that attempt to explain what happened — from epidemic diseases to foreign invasions. The leading theory, however, is that sudden climate change brought about an extremely severe "megadrought" that lasted 200 years.
Because many of the great Mayan cities were situated in seasonal deserts, residents were entirely dependent on the vast and complex rainwater storage system. Any fluctuations in annual rainfall averages meant dire consequences. As these cities were flung into a centuries-long drought, it didn't take long before the citizenry dispersed and fragmented.