A team led by Gregory Springer from Ohio University was using the ratios of carbon isotopes in stalagmites to study historic drought cycles in North America when they found something surprising. A stalagmite from a cave in the mountainous Buckeye Creek basin in West Virginia showed evidence of a large change in the local ecosystem beginning around 100 BC. The results were particularly intriguing because an archaeological dig in a nearby cave had turned up evidence of a Native American community living there around the same time.

In order to gather more evidence, the team examined stream sediments, finding very high levels of charcoal beginning around 2,000 years ago, as well as a carbon isotope signature similar to that in the stalagmite.

Taken together, the researchers say in a paper published in the Holocene, the two strands of evidence suggest that Native Americans were involved in large-scale clearing and burning of forests, probably to create fields and to stimulate the growth of nut trees. This would have led to significant releases of CO2 and methane. ‘Long before we were burning fossil fuels, we were already pumping greenhouse gases into the atmosphere,’ Springer said. ‘It wasn’t at the same level as today, but it sets the stage.’

June 2010