Papers published in Science of Climate Change by Harde and Salby (2021), and by Berry (2021) contend that the well documented growth of atmospheric CO2 in recent decades is predominantly a natural phenomenon rather than human caused. Both papers are wrong on two counts. First, they focus only on their own (suspect) calculations of anthropogenic atmospheric carbon levels, rather than on measured total carbon levels. The present concentration of anthropogenic carbon in the atmosphere, even correctly calculated, does not establish the human contribution to the rise in total atmospheric carbon. Second, the models these authors develop for determining present anthropogenic atmospheric carbon levels are incompatible with 14C data. The sources of background “anomalous 14C” postulated by Harde and Salby fall well short of being large enough to salvage their model. A highly questionable assumption built into Harde and Salby’s model is explicitly identified.

A misunderstanding of the definition of the variable “Delta14C” , commonly used in radiocarbon dating and tracing applications to quantify 14C levels, has led at least thee authors to reach wrong conclusions about the fate of carbon introduced into the atmosphere. Models motivated by the mistake are excluded by the very same 14C data, properly interpreted.