Researcher Cites Role of Ancient Farming in Climate Change

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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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