“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.