Did Major Climate Change Begin Causing Humans 8,000 Years Ago?
"My guess is that the author is mistaken, but he is no dope. My reason for this opinion is that 8,000 years ago, there just were not enough humans to make a significant difference in climate."
That would SEEM to be common sense, but we don't really know how much CO2 it would take. A globally distributed source of CO2 for a few kYears could be a bigger factor, with fewer total emissions, than the periodic contributions of lightning fires or volcanism. Remember, by this time humans were everywhere...