Did the Mayan civilization end because of climate change?

Unlike other vanished civilizations, at least some of the Mayans' written records have survived, which has enabled scholars to partially reconstruct their history. But those tantalizing clues have only made the mystery of their decline more frustrating [source: Diamond]. Over the years, researchers have developed various theories about what caused the decline of Mayan civilization. Here are three of the most prominent ones:

While scientists aren't completely discounting all those possibilities, in recent years they've added another theory. Increasingly, they suspect that Mayan society collapsed because of the stress of climate change -- a risk that faces modern civilization today, as we burn huge amounts of fossil fuels and spew greenhouse gas emissions that warm the planet. The Mayans, though, didn't have gas-guzzling SUVs, and they didn't need coal-burning power plants to power their big-screen TVs and air conditioners, since they didn't have those either. So what was the deal with them? We'll look at possible explanations in the next section.

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.

You've probably heard the claims that the Mayan calendar prophecies the end of the world in 2012 -- an idea that for some reason is tremendously appealing to modern-day apocalypse junkies, even though it's totally incorrect. Here's the 411: While December 21, 2012 corresponds to the end of a Mayan calendar cycle, the calendar calls for another cycle to begin immediately after that [source: Wolchover].

That said, there are some lesson from the Mayan collapse that we ignore at our own peril. Scientists worry that we are repeating the same pattern of deforestation that may have exacerbated climate change in Central America more than a millennium ago, except on a far more massive scale. Trees are about 50 percent carbon, and in the U.S alone, they presently absorb between 1 and 3 million metric tons (984,206 to 2,952,691 tons) of atmosphere-warming carbon dioxide, which offsets between 20 and 46 percent of what Americans spew into the atmosphere by burning coal and gasoline. But when we cut down trees or burn them, they release their stored carbon into the atmosphere, and they aren't around to absorb any more of it [source: Johnson].

Over the past several centuries, the U.S. has cut down about 90 percent of the forests that once covered the continent, and what remains is still in peril. In the Pacific Northwest, for example, about 80 percent of the old-growth forestland is slated for eventual logging [source: University of Michigan]. Worse yet, in nations in the developing world -- Latin America, the Caribbean, Africa, and Asia -- once-lush forests have been disappearing at an alarming rate, thanks to logging, agriculture, and need for living space. In recent years, there's been some international progress in slowing the rate of deforestation, but we still face the risk that it will push us even faster into climate chaos [source: Johnson]. It's a problem that we must work harder to solve.