A new study led by Ohio University scientists suggests that early Native Americans left a bigger carbon footprint than previously thought, providing more evidence that humans impacted global climate long before the modern industrial era.

Chemical analysis of a stalagmite found in the mountainous Buckeye Creek basin of West Virginia suggests that native people contributed a significant level of greenhouse gases to the atmosphere through land use practices. The early Native Americans burned trees to actively manage the forests to yield the nuts and fruit that were a large part of their diets.

"They had achieved a pretty sophisticated level of living that I don't think people have fully appreciated," said Gregory Springer, an associate professor of geological sciences at Ohio University and lead author of the study, which was published a recent issue of the journal The Holocene. "They were very advanced, and they knew how to get the most out of the forests and landscapes they lived in. This was all across North America, not just a few locations."

Initially, Springer and research collaborators from University of Texas at Arlington and University of Minnesota were studying historic drought cycles in North America using carbon isotopes in stalagmites. To their surprise, the carbon record contained evidence of a major change in the local ecosystem beginning at 100 B.C. This intrigued the team because an archeological excavation in a nearby cave had yielded evidence of a Native American community there 2,000 years ago.

Springer recruited two Ohio University graduate students to examine stream sediments, and with the help of Harold Rowe of University of Texas at Arlington, the team found very high levels of charcoal beginning 2,000 years ago, as well as a carbon isotope history similar to the stalagmite.

This evidence suggests that Native Americans significantly altered the local ecosystem by clearing and burning forests, probably to make fields and enhance the growth of nut trees, Springer said. This picture conflicts with the popular notion that early Native Americans had little impact on North American landscapes. They were better land stewards than the European colonialists who followed, he said, but they apparently cleared more land and burned more forest than previously thought.

"Long before we were burning fossil fuels, we were already pumping greenhouse gasses into the atmosphere. It wasn't at the same level as today, but it sets the stage," Springer said.

This long-ago land clearing would have impacted global climate, Springer added. Ongoing clearing and burning of the Amazon rainforest, for example, is one of the world's largest sources of greenhouse gas emissions. Prehistoric burning by Native Americans was less intense, but a non-trivial source of greenhouse gases to the atmosphere, he said.