Global warming sparked by ancient farming methods

http://www.cnn.com/2009/TECH/science/08/18/ancient.global.warming/index.html

Global warming is something that has slowly been affecting the earth for many years, but just when did it start? A new study shows that ancient man may have started global warming through massive deforestation and burning that could have permanently altered the Earth's climate. This study, done by the University of Virginia shows that over thousands of years, farmers burned down so many forests on such a large scale that huge amounts of carbon dioxide were pumped into the atmosphere. Causing the earth to heat up, thus starting global warming. That slashing and burning on such a large scale spewed enormous amounts of greenhouse gasses into the atmosphere and warmed the planet, the study says.

Lead study author William Ruddiman says "It seems like a common-sense idea that there weren't enough people around 5, 6, 7,000 years ago to have any significant impact on climate. But if you allow for the fact that those people, person by person, had something like 10 times as much of an effect or cleared 10 times as much land as people do today on average, that bumps up the effect of those earlier farmers considerably, and it does make them a factor in contributing to the rise of greenhouse gasses."