http://earthobservatory.nasa.gov/IOTD/v ... c=eoa-iotd
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.Sometime during the ninth century A.D., an apparently prosperous Mayan society collapsed within decades. Why? Could the collapse of the Mayan civilization be a warning to us today?
One possible explanation for the downfall is drought. Central America is naturally prone to drought, but one recent study suggests that Mayan activities may have deepened the dry conditions. In an effort to sustain one of the highest population densities in history, the Mayans transformed the land. They removed nearly all of the forest and replaced it with agricultural land. The top map shows how little native forest (dark green) remained at the end of the Mayan period.
By cutting down the forest, the Mayans essentially changed their local climate. When NASA scientist Ben Cook examined Mayan land use in the Goddard Institute for Space Studies general circulation model, he found that the climate was warmer and drier during the rainy season (June, July, and August) than it would have been had natural forest remained in place. Though deforestation didn’t cause a drought, it amplified natural droughts when they occurred. The center and lower images illustrate the change. Places that are drier (brown) and warmer (red) than normal correspond to areas where the forest had been cleared.