DECLINE IN CONCENTRATION OF 13C RELATIVE TO 12C IN ATMOSPHERIC CO2
FIGURE 14.17 As the concentration of atmospheric CO2 increased after 1800, the relative concentration of 13C in atmospheric CO2 has declined, indicating that the buildup of atmospheric CO2 is largely the result of the burning of fossil fuels and biomass, which contain less 13C relative to 12C. (Data from Friedli et al., 1986, and Scripps CO2 Program)