Forest Razing by Ancient Maya Worsened Droughts, Says Study

Human-Influenced Climate Change May Have Contributed to Society’s Collapse

So, they increased the local albedo, cooled the surface and caused droughts… Okay. Cooling is known to be really bad for people and primary productivity.

For six centuries, the ancient Maya flourished, with more than a hundred city-states scattered across what is now southern Mexico and northern Central America. Then, in A.D. 695, the collapse of several cities in present day Guatemala marked the start of the Classic Maya’s slow decline. Prolonged drought is thought to have played a role, but a study published this week in the journal Geophysical Research Letters adds a new twist: The Maya may have made the droughts worse by clearing away forests for cities and crops, making a naturally drying climate drier.

“We’re not saying deforestation explains the entire drought, but it does explain a substantial portion of the overall drying that is thought to have occurred,” said the study’s lead author Benjamin Cook, a climate modeler at Columbia University’s Lamont-Doherty Earth Observatory and the NASA Goddard Institute for Space Studies.

More than 19 million people were scattered across the Maya empire at its height, between A.D. 250 and A.D. 900. Using population records and other data, the study authors reconstructed the progressive loss of rainforest across their territory as the civilization grew. The researchers ran computer simulations to see how lands newly dominated by crops would have affected climate. In the heavily logged Yucatan peninsula, they found that rainfall would have declined by as much as 15 percent while in other Maya lands, such as southern Mexico, it would have fallen by 5 percent. Overall, the researchers attributed 60 percent of the drying estimated at the time of the Maya’s peak to deforestation.

As crops like corn replace a forest’s dark canopy, more sunlight bounces back into space, said Cook. With the ground absorbing less energy from the sun, less water evaporates from the surface, releasing less moisture into the air to form rain-making clouds. “You basically slow things down—the ability to form clouds and precipitation,” he said.


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6 responses to “Forest Razing by Ancient Maya Worsened Droughts, Says Study

  1. Wouldn’t most of the precipitation in the Yucatan come from the Caribbean?
    I don’t understand how this effect could be

    • oops
      I was going to say I don’t understand how the effect of deforestation on rainfall could be so large

      • It’s been shown that deforestation has a significant effect on precipitation, enough to push semi-arid regions into arid (the Sahel for instance). As a straw that breaks the camel’s back, maybe. However, I think that they have far too much conviction in their conclusion. Hank has the more traditional and logical explanation. Droughts kill people, not nations, politics and war kill nations.

        • I can accept that deforestation can push a semi-arid region over the edge or that a drought can push a civilization on the brink over the edge, but the explanation given in the last paragraph makes no sense to me.
          Okay, I can see that the albedo of the canopy is lower than that of the crops, but underneath the canopy the ground is cooler in the shade of the rain forest than in the full sun, so the canopy should retain water at ground level, shouldn’t it?
          The prevailing winds should be bringing rain from clouds that formed over the Caribbeans. The statement that deforestation slows down “the ability to form clouds” seems wrong.

  2. The models are telling a very different story from that of anthropology and archeology. The Maya collapse was not gradual as Cook describes. It was rather sudden. So sudden that they left belongings stored in a way that made it clear they intended to return. They also abruptly abandoned numerous building construction projects, indicating that there was expansion of the cities taking place at the time.

    The reason for the sudden collapse of the Maya civilization was twofold: there was a political upheaval of the empire that resulted in brutal wars between Maya city states, disrupting trade routes and throwing the dynasty and their religion into chaos. In the midst of the political and social collapse a rapid onset drought dealt the final blow. The Classic Maya empire fractured into mostly small uncoordinated bands. The bands lacked the political cooperation to repopulate and rebuild the once great empire.

    Not all of the cities of the Maya empire were abandoned. Uxmal, Chichén Itzá and Mayapán continued to flourish under city state rule following the Classic Maya collapse. They remained cultural centers up to the invasion of the Spanish.

  3. Well, there’s certainly still some deforested areas in and around there. How’s the drought and why hasn’t Gautemala dried and blown away? This is reminiscent of defenders of the rain forests claiming that deforestation was what torched the Sahara. Apparently, the Sahara forest comes and goes on a time scale of thousands of years. They’re looking at one tree in a forest.

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