The Maya city of Tulum. Photo by: Rhett A. Butler.
Researchers have garnered further evidence for a smoking gun behind the fall of the great Maya civilization: deforestation. At the American Geophysical Union (AGU) conference, climatologist Ben Cook presented recent research showing how the destruction of rainforests by the Mayan ultimately led to declines in precipitation and possibly civilization-rocking droughts. While the idea that the Maya may have committed ecological-suicide through deforestation has been widely discussed, including in Jared Diamond’s popular book Collapse, Cook’s findings add greater weight to the theory.
Modeling by Cook and his colleagues showed that replacing rainforest with agriculture led to increasing reflectivity of the land surface, known as albedo. This increase in reflectivity changed rainfall patterns.
“Farmland and pastures absorb slightly less energy from the sun than the rainforest because their surfaces tend to be lighter and more reflective,” explained Cook, with NASA’s Goddard Institute for Space Studies (GISS) and Columbia University’s Lamont-Doherty Earth Observatory in New York City, in a press release from AGU. “This means that there’s less energy available for convection and precipitation.”
Prior to the arrival of Columbus, the central American empire cut forests far-and-wide to feed a growing population. However, they didn’t realize that they were exacerbating their own decline. By a little after 900 AD the Maya civilization had largely collapsed.
 Aerial view of Amazon rainforest landscape scarred by open pit gold mines. Photo by: Rhett A. Butler. |
To tease out the smoking gun, Cook turned to the most detailed and accurate reconstructions yet of land-cover in the Yucatan peninsula before and after the collapse. The reconstruction shows that only a small percentage of forest survived in the Yucatan Peninsula between 800 and 950 AD.
Running climate models with the new data, Cook saw a clear change: precipitation fell by 10 to 20 percent generally. The effect was largest around the big Mayan population centers. During the Maya’s last stand between 800 and 950 AD rainfall fell 20 percent. The models also agree with precipitation records of the period taken from cave stalagmites.
Still, Cook says it’s likely that a number of impacts caused the decline of the Maya.
“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,” he says.
But a mega-drought would have crippled agriculture for a growing population, dried up vital water sources, and likely destabilized political and religious authority.
Cook’s findings buttress a previous study last year by Robert Oglesby, which also argued that deforestation played a significant role in the Maya collapse.
Following the Maya collapse, the Aztec civilization rose in the region. However, that civilization fell to smallpox and a small Spanish invasion force in 1519. Brought by the Europeans, smallpox killed ofd a significant, though highly debated, percentage of the indigenous people. Between 1500 and 1650 AD, forests returned with the population decline.
Scientists in recent years have begun to increasingly link precipitation patterns with tropical forests. A 2005 NASA study found that smoke from burning forests inhibits cloud production, decreasing rainfall. Meanwhile, a 2009 study in the Proceedings of the National Academy of Sciences found that historic deforestation in China and India caused a change in the monsoon, decreasing rainfall in China by 10 percent and India by 30 percent. Consequences may range beyond the region where deforestation occurs: according to NASA, the Amazon influences rainfall from Mexico to Texas; the Central American rainforest affects precipitation in the Midwest; and the tropical forests of Southeast Asia impacts rainfall in China and the Balkans. The most radical theory, however, from two Russian scientists, Victor Gorshkov and Anastassia Makarieva, argues that forests are a key driver of global precipitation. Acting as pumps, forests push precipitation from coastal areas into the continental interiors. In other words, a loss of forest may bring drought to continental centers, for example drought in Australia may be explained by the widespread loss of its coastal forests.
Even beyond precipitation, forests provide many services to human-kind: sequestering carbon, preserving the bulk of the world’s biodiversity, providing life-saving medicines, conserving vast freshwater reservoirs, and safeguarding indigenous cultures.
If the intriguing theory that the Maya did themselves in through deforestation holds, it provides a stark lesson to the world today. According to a recent analysis from the UN Food and Agriculture Organization (FAO) the world has lost 72.9 million hectares of forest between 1990 and 2005, an area twice the size of Germany. Logging, monoculture plantations, large-scale agriculture, mining, fossil fuel industries, roads, and other impacts are largely behind the current decline in the world’s forests.
“We could see these sorts of things happen again,” Cook said pointing to current forest loss in Central America.
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