A deconvolution of the tree ring based δ13C record

We assumed that the tree‐ring‐based 13 C/ 12 C record constructed by Freyer and Belacy (1983) to be representative of the fossil fuel and forest‐soil induced 13 C/ 12 C change for atmospheric CO 2 . Through the use of a modification of the Oeschger et al. ocean model, we have computed the contribution of the combustion of coal, oil, and natural gas to this observed 13 C/ 12 C change. A large residual remains when the tree‐ring‐based record is corrected for the contribution of fossil fuel CO 2 . A deconvolution was performed on this residual to determine the time history and magnitude of the forest‐soil reservoir changes over the past 150 years. Several important conclusions were reached. (1) The magnitude of the integrated CO 2 input from these sources was about 1.6 times that from fossil fuels. (2) The forest‐soil contribution reached a broad maximum centered at about 1900. (3) Over the 2 decade period covered by the Mauna Loa atmospheric CO 2 content record, the input from forests and soils was about 30% that from fossil fuels. (4) The 13 C/ 12 C trend over the last 20 years was dominated by the input of fossil fuel CO 2 . (5) The forest‐soil release did not contribute significantly to the secular increase in atmospheric CO 2 observed over the last 20 years. (6) The pre‐1850 atmospheric values must have been in the range 245 to 270×10 −6 atmospheres.