Interpretation of the Northern Hemispheric Record of 13C/12C Trends of Atmospheric CO2 in Tree Rings

  • Hans D. Freyer


The present long-term increase of atmospheric CO2 has been accompanied by changes in the isotopic composition of its carbon atoms. Both the ratios of stable 13CO2/12CO2 and radioactive 14CO2/12CO2 have decreased as a result of anthropogenic activity. The decrease of the latter, until the beginning of nuclear testing caused an increase in the mid-1950s, is almost exclusively due to dilution of atmospheric CO2 resulting from fossil fuel burning, from which the 14C isotope had already decayed. The decrease of the 13C/12C ratio is a better measure of total anthropogenic activity because it reflects not only fossil fuel burning but also CO2 released as a result of deforestation and agricultural manipulation of the soil. The CO2 from both of these sources is marked by a δ13C deficit of about 18 to 20‰ (PDB scale; e.g., Freyer 1979c).


Northern Hemisphere Tree Ring Atmospheric Carbon Dioxide Quercus Robur Regional Trend 
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© Springer Science+Business Media New York 1986

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  • Hans D. Freyer

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