Fall of Empires Hastened 'Little Ice Age'

Dec. 22, 2008 -- The vast empires of the Incas and Aztecs were highly advanced. They kept detailed tax records, built elaborate temples, and at their height, Central and South America boasted a thriving population of as many as 60 million souls.

But their grand civilizations bore another trapping of modernity, scientists have found, one that until recently was thought unique to our industrialized world: human-induced climate change.

In the 16th century, the diseases Europeans brought to the New World decimated native peoples. With no natural defense against smallpox, yellow fever, and a host of exotic new pathogens, 90 percent of the population was dead by 1600.

"We're talking about wiping out about 9 percent of the world's population at the time," said Richard Nevle of Bellarmine College Preparatory School, in San Jose, Calif.

Related Content:

According to Nevle and co-author Dennis Bird of Stanford University, the killing left a lasting impact on the global climate. Suddenly as much as 500,000 square kilometers (193,051 square miles) of cleared farmland was no longer being tended, an area slightly larger than California. And as the rainforest crept back in, it vacuumed carbon dioxide out of the atmosphere in the process.

In all, the authors estimate that reforestation of South and Central America could've removed up to ten billion tons of carbon from the atmosphere.

Around the same time, climate records show from that global temperatures cooled about 0.1 degrees centigrade (about 0.2 degrees Fahrenheit) from 1500 until 1750. But in northern Europe the dip was far more dramatic, and came to be known as the Little Ice Age.