BunsenBwog: Mayans, Droughts, and the True Price of Corn

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Can you avoid the barrels?

Real life Donkey Kong

This week, our aspiring anthropologist, Zach Kagan, trekked down to 112th and Broadway to talk with climate scientist Benjamin Cook about his research on the real Mayan apocalypse, not the one purported to happen on December 21st, 2012.

Climate science tends to obsess with the far future. What will climate patterns be like in five, ten, fifty years from now? Will there be enough clean water for our grandchildren? Can we impede the rate of climate change or should we all just get used to the taste of nutritious Soylent Green?

While these questions are important, others like Columbia/NASA researcher Benjamin Cook and his collaborators are looking for answers from the past. Not the geologic past either, but specifically 1,300 years ago: the collapse of the Mayan civilization. The Classic Maya collapse has troubled generations of historians and archeologists. Why was it that, after centuries of expansion and increasing sophistication from 300 AD to 900 AD, the Mayans declined so rapidly? Cities were abandoned and people fragmented into smaller groups mainly along southern Mexico and Guatemala. There are dozens upon dozens of theories for this collapse, ranging from hostile invasions to revolts to disease. However, the most accepted one has recently been the drought theory.

The idea is that the Mayans suffered from a prolonged period of intense drought lasting for 200 years. Though it might not be as exciting as the climatic battle for Chichén Itzá, but water is crucial for producing food that sustains a society. After all, a society can only function as long as it produces enough food for everyone to eat, even if some people are rulers, priests, or merchants instead of farmers. A structured and heavily stratified society like the Mayans needed a large food surplus to exist. No water means no food surplus, which means no Mayan civilization. Evidence collected from tree rings, cave formations, and lakebeds seems to support this theory.

The drought theory makes the Classic Maya Collapse look like an open and shut case, but there is one loose end. What caused this 200-year drought? The Mayans could have been just unlucky, but they were used to droughts in the area and had withstood many before. One hypothesis is that the Mayans exacerbated the drought by clearing-cutting the forests and replacing them with farmland. Thick jungles absorb a lot of light, facilitating evapotranspiration and increasing the rate of rain cloud formation. When the Mayas replaced larger tracts of the forest with corn crops it increased the area’s albedo (the amount of light reflected back into space) and decreasing the amount of water that was sent back into the atmosphere.

Cook and his team wanted to test this theory. Using a computational climate model developed at NASA’s Goddard Institute for Space Studies (GISS, located right above Tom’s Diner), Cook analyzed the atmospheric conditions of the Mayan world. At their height, the Mayan population was around 19 million. Today, if you are trying to feed a growing population, you have a variety of options to produce more food: use fertilizers, irrigate, and use underground aquifers to increase crop yield. The Mayans, along with any preindustrial society, did not have that capability. If they wanted more food, it meant they needed to farm more land. Using the geological conditions of the Yucatan Peninsula, Cook calculated how much forest the Mayans would need to clear just to feed the entire population. According to the GISS climate model, that degree of deforestation would have resulted in a 5% to 20% decrease in rainfall.

Anything over a 10% decrease in rainfall can be considered a drought, so a 20% drop would be extremely taxing on the Mayan Civilization. But, Cook’s calculation only accounts for half of the drying during this period, which means that Mayan deforestation intensified an already occurring drought to the point where their social order crumbled under the strain.

It seems like a cautionary tale, warning the dangers of heedless expansion, but what can we really take from the Mayan collapse? Deforestation continues in South America, the Asia-Pacific, and Africa at alarming rates, often for the sake of creating farmland or grassland for cattle. Meanwhile, after over a thousand years, the lands that the Mayans once inhabited are now again lush forests with plentiful rainfall. However, few of us want to wait a thousand years for land to recover and become suitable for farming.  We have a water problem as well, but it is more complex than a lack of rainfall. Farmlands get pumped full of enough water and fertilizers until they can grow just about anything, but this system isn’t sustainable, especially with the threat of a looming water shortage.

Before you break out the Soylent Green, take a deep breath. There is actually a lot we can do to avoid eating ourselves to extinction à la the Mayans. Chiefly among them consuming less water-intensive crops like corn and beef. Given that the modern American actually eats more corn products than the average Mayan did a thousand years ago, living sustainably might be harder than we think. “I’m a heady [sic] optimist,” says Cook, “we can be successful with a decent standard of living and not go hungry.”

Special thanks to Benjamin Cook and NASA GISS.

Sherpa training course via Wikimedia Commons.

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  1. Anonymous  

    this reminds me that I never finished reading Jared Diamond's Collapse. I really should. I want to find out what he says about the Mayan collapse.

  2. Anonymous

    A very fine article, BunsenB, thanks for reminding us of this important consideration.

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