A new paper published in Quaternary Science Reviews reconstructs CO2 levels during the termination of the last ice age and finds CO2 spiked to levels near or even exceeding those of the present, obviously without any human influence. According to the authors, "The record clearly demonstrates that [CO2 levels were] significantly higher than usually reported for the Last [Glacial] Termination," with levels of up to ~425 ppm about 12,750 years ago, which exceeds the present CO2 concentration of 395 ppm.
http://hockeyschtick.blogspot.com/2013/ ... igher.html
source of above graph
Scientists: Carbon dixode at highest level in 800,000 years
ScienceDirect, Oct 2009
Last Time Carbon Dioxide Levels Were This High: 15 Million Years Ago, Scientists Report