It’s definitely true that CO2 has increased in the past, especially in the glacial/interglacial periods. During this period of time, CO2 has increased and decreased by 100ppm, from roughly 180-330ppm. These increases occurred over a 400,000 year period. This was roughly 5,000-20,000 years depending on the glacial cycle. However, with that being said, Sparky, we’ve seen an increase of 100ppm in 150 years. Click here to look at the comparison between slow glacial termination vs the industrial revolution. When scientists analyzed the isotopes of the carbon/oxygen atoms comprising the atmospheric CO2, which is similar to carbon dating, they determined a human fingerprint of sorts. They discovered old carbon which is a result of fossil fuel deposits, then combined with newer oxygen found in the air nowadays. The present and continued combustion of hydrocarbons is definitely the source of increasing CO2 levels.