The atmosphere is not the only reservoir for civilization's emissions of carbon.  This page brings the oceans into the picture.  Over longer time scales, most of the carbn emitted today will end up in the ocean.

 

 Ocean Acidification: Explained in 60 seconds

 

Source  WXhift  |  climate indicators: ocean acidification [web + youtube]

 

CO2 Past.  CO2 Present.  CO2 Future.