While our modern civilization is driving global warming by polluting the atmosphere, the Earth's climate is affected by other factors, such as changes in solar activity and volcanoes [source: U.S. Global Change Research Program]. The Mayans' plight seems to be largely the result of such natural cycles.
Scientists who've studied mineral deposits left by dripping water in caves have been able to construct a 2,000-year-long history of weather patterns in Central America. In an article published in Science in 2012, the researchers revealed that for the first several hundred years of Mayan civilization, the Mayans benefited from unusually wet weather that made it easier to grow crops, and enabled the Mayan population to expand. That also made the Mayan kings look pretty good, because they could claim credit for conducting the blood sacrifices and other rituals that kept the rains coming [source: Zabarenko]. (It's hard to say whether or not they really believed in their own magical powers.)
But around 660 AD, the weather changed, and rain became more infrequent. That probably created a lot of tensions in Mayan society, because "they're doing the ceremonies and nothing's happening," Pennsylvania State University anthropologist Douglas Kennett explained in a 2012 interview with Reuters [source: Zabarenko].
Additionally, the Mayans also may have accelerated climate change by cutting down the forest around them, probably for fuel and to create wood plaster for use in their ornate buildings [source: Diamond]. From studying pollen found in ancient layers of Central American lake sediment, scientists learned that around 800 AD, about a century before the Mayan civilization began to crumble, tree pollen disappeared almost completely and was replaced by pollen from weeds. That suggested that the region's forests had all but disappeared.
Without trees and their root systems to keep soil in place, erosion would have worsened, carrying away fertile topsoil, which would have crippled Mayan agriculture. Additionally, trees function as natural air conditioners, drawing water through their leaves and cooling the local air when the water evaporates [source: U.S. Forest Service]. You can experience this same effect if you live in a city. In a park with trees, it's going to seem cooler than it does out in a city block with just buildings and asphalt all around. Computer simulations indicate that the region's temperature would have increased by as much as 6 degrees Fahrenheit [source: NASA].
That change would have been enough to alter the weather even more. Researchers who've analyzed changes in river sediment have found that in the century after deforestation, rainfall declined, with intense multi-year droughts occurring around 810, 860 and 910 AD [source: Haug, et al.].
Since the Mayans probably depended upon rain captured in reservoirs for drinking water, they would have faced not only hunger, but thirst as well [source: NASA]. It's not hard to imagine how a panicked Mayan population would have fled their once-great cities, as their way of life collapsed into a pre-Columbian version of "Mad Max." In the next section, we'll talk about whether their plight should be a warning to us.