New clues about what caused the collapse of Mayan civilizationS

The abandoned cities and giant monuments of the Maya, found throughout the Yucatán, are one of the greatest mysteries in human history. Why did this great empire collapse suddenly in 950 AD, leaving its massive urban centers to be consumed by jungle? New evidence suggests that the Mayans may have created such vast farms that they managed to change the local climate in a catastrophic way.

It's long been surmised that the Mayan empire fell largely because of a 200-year drought that struck the region in 800 AD, but now it appears that the drought may have been amplified by Mayan agricultural practices. At the empire's height, in 800, scientists estimate that the entire Yucatán had been stripped of forests to make way for farms to feed Mayan urbanites. Farmers burned the native plants so they could plant maize and other edibles. By the time Europeans arrived on the continent, however, the Mayan cities had long ago been swallowed by jungle again. The Aztec empire was also an agricultural powerhouse, but hadn't deforested nearly as much land as the Maya.

Ben Cook, a climatologist who works with groups at NASA and Columbia University, has just published an analysis of historical climate models that show how the deforestation of the Yucatán could have helped tip the climate over into a drought. By analyzing climate simulations, Cook was able to determine that rainfall fell by 20 percent in the period between 800 and 950. It's likely that loss of the forest increased the albedo, or reflectivity, of the land's surface. With more light bouncing back into space, the area would have less energy to produce rainfall.

New clues about what caused the collapse of Mayan civilizationS

In a release about his work from NASA, Cook said:

I wouldn't argue that deforestation causes drought or that it's entirely responsible for the decline of the Maya, but our results do show that deforestation can bias the climate toward drought and that about half of the dryness in the pre-Colonial period was the result of deforestation.

In a sense, the Mayans were victims of their super-advanced agricultural techniques. They were the factory farmers of what Westerners would call the Medieval era. Just as people do in cities and farms today, the Maya managed to completely alter their environments and even change the climate.

Climatologist Dorothy Peteet, also associated with NASA and Columbia, has analyzed core samples to reconstruct historical climate conditions. She amplifies Cook's claims, explaining that deforestation could lead to local droughts in areas like the Northeast United States. She said:

People don't generally think about the Northeast as an area that can experience drought, but there's geologic evidence that shows major droughts can and do occur. It's something scientists can't ignore. What we're finding in these sediment cores has big implications for the region.

Read more about ancient climate change and the future of drought at NASA.

Photo by Rui Vale de Sousa via Shutterstock.