NOTICE (September 2017): Data previously stored at the CDIAC archive are being transitioned to the new, ESS-DIVE archive. This website provides access to the CDIAC data during the transition. If you have any questions regarding the new archive or the data transition, please contact

image image image image

Carbon-13 in CO2

Carbon-13 in CO2 is decreasing, as the fraction of atmospheric CO2 that is realized from combustion of fossil carbon is increasing. Ratios of 13C/12C in CO2 tend to be lower in the Northern Hemisphere, suggesting a fossil-fuel source that resides mainly in the Northern Hemisphere.