Correcting an Error in Some Interpretations of Atmospheric 14C Data

Abstract

The variable “∆14C”, commonly used in radiocarbon dating and tracing applications to quantify 14C levels, is a measure of the ratio of the radioisotope 14C to other carbon in a sample. After atmospheric nuclear testing in the 1950’s and 1960’s nearly doubled atmospheric 14C, the later evolution of ∆14C allowed insights into the dynamics of carbon exchange between the atmosphere and terrestrial and marine sinks. But a few authors without backgrounds in isotope measurements have confused ∆14C with excess 14C concentration. They erroneously interpret the present recovery of ∆14C to near its pre bomb test value as evidence that atmospheric 14C concentration has returned to its earlier value. From this they reach further incorrect conclusions about the fate of anthropogenic CO2 introduced into the atmosphere by fossil fuel burning. An estimate of the true time dependence of atmospheric 14C concentration over the past century, calculated from averaged atmospheric ∆14C and CO2 data is presented. The data show that 14C concentrations remain over 30% above 1950 values, and have begun to increase, even as ∆14C continues to fall. This confirms the prediction of a conventional model of the carbon cycle. The unconventional models of carbon dynamics motivated by the mistake, on the other hand, are excluded by the properly interpreted 14C data.