Researcher Cites Role of Ancient Farming in Climate Change

By David A. Fahrenthold
Washington Post Staff Writer
Monday, September 28, 2009

Has climate change been around as long as the pyramids?

It is an odd-sounding idea, because the problem is usually assumed to be a modern one, the product of a world created by the Industrial Revolution and powered by high-polluting fossil fuels.

But a professor emeritus at the University of Virginia has suggested that people began altering the climate thousands of years ago, as primitive farmers burned forests and built methane-bubbling rice paddies. The practices produced enough greenhouse gases, he says, to warm the world by a degree or more.

Other scientists, however, have said the idea is deeply flawed and might be used to dampen modern alarms over climate change.

Understanding the debate requires a tour through polar ice sheets, the inner workings of the carbon molecule, the farming habits of 5,000-year-old Europeans and trapped air bubbles more ancient than Rome.

"The greenhouse gases went up, and they should have gone down" many thousands of years ago, said U-Va.'s William Ruddiman. "Why did that happen?"

His answer is based on circumstantial evidence. Ruddiman said two events in world history -- an apparent shift in the composition of the atmosphere and the first explosion of human agriculture -- took place at nearly the same time.

"Greenhouse gases do something they never did before," Ruddiman said. "And humans do something the Earth [had] never seen before."

Ruddiman first presented his idea of ancient climate change in 2003. But he returned to the subject last month, in a paper intended to rebut one major criticism -- that there were not enough people on the planet thousands of years ago for their emissions to make a difference.

Ruddiman's response: yes, there were. And in those days, one farmer was as destructive as multiple farmers are today.

He and Erle Ellis, a professor at the University of Maryland Baltimore County, wrote in the journal Quaternary Science Reviews that early farmers did not have modern fertilizer or factory-made tools, but they did have a lot of land. They would clear an area by cutting or burning it, farm the ground until it was nearly barren and move on.

"Those tens of millions [of people] had the impact of hundreds of millions, because per person, they had 10 times the impact," Ruddiman said. "And that's enough to start the curve turning around."

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