The isotopic ratios tell a different story. 

http://www.realclimate.org/index.php/archives/2004/12/how-do-we-know-that-recent-cosub2sub-increases-are-due-to-human-activities-updated/

CDIAC (who I've submitted to in the past and are amazing people) have been directly measuring this ratio since 1990.

http://cdiac.ornl.gov/trends/co2/graphics/delta_13c_in_co2.html