Studies: A Little Warming Can Destroy Societies

So some mysterious mechanism that we don't yet understand "amplified" the effect in the Yucatan, the scientists suggest, wreaking havoc on local weather patterns.

Whatever the cause, the droughts appear to have been real, based on the core sediments from the bottom of the lake. But weather was not the only thing ripping at the Mayan culture.

Experts have spent decades deciphering the writings of the Maya, and the story that emerges is not entirely flattering. They tell of local rulers who waged war on other cities; of torture and mutilation and human sacrifice.

Like the Maya, the Anasazi built great edifices with as many as 1,000 rooms, which they abandoned around 1300 following a severe drought that lasted from 1276 to 1299. Those carefully engineered structures and other elaborate monuments were built on the backs of laborers, some of whom must have been unhappy with the process.

So it's hard to say how much of a role the drought had. Like the Mayans, many Anasazi probably found their culture increasingly difficult to bear and just drifted off. But the drought, no doubt, made everybody's life harder. By the time the Spaniards conquered Central America in the 16th century, the relics of the Mayan civilization had been buried beneath centuries of jungle growth.

Most likely, drought contributed to the demise of the Mayan culture by wiping out agricultural resources that had become vital to an urban population that some experts believe numbered 2 million souls. Whether it was the primary cause of the collapse, or just one of many factors, will be debated for decades by experts. But there is a lesson in it for the modern world.

Brace for Fast Change

If the global climate is changing, and many experts believe it is, then we could be in for some real surprises ahead. Donald Kennedy, former president of Stanford University and now editor of the journal Science, has warned that we are making a big mistake if we expect a gradual, steady warming trend because of changing global climatic conditions, like the greenhouse effect that many experts believe is resulting from the burning of fossil fuels. Many changes will be abrupt, Kennedy argues.

"We may be unwise to rest our economic projections on the assumption that the probable climate future is a slow, steady ramp of increasing average global temperature," he told a symposium last year at the State University of New York.

He cited El Niño as one example of just how vulnerable we are to changing climatic conditions. An El Niño is caused by warming of the waters in the southwest Pacific Ocean, yet in recent years El Niños have caused flooding in North America and so much loss in rainfall in Africa that corn yields in Zimbabwe dropped by 10 percent.

"I think our society ought to entertain, now, the prospect that a sudden shift in the climate regime is a highly possible consequence of the warming trend we are experiencing now," Kennedy told the New York symposium.

In other words, hold on to your rain bonnets. We may be in for quite a ride.

Lee Dye’s column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.

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