“Fossil carbon is a negligible component of the net atmospheric CO2 addition.”

A new study argues that the common practice of attributing the post-industrial rise in atmospheric CO2 entirely to fossil-fuel combustion is mathematically inconsistent with available isotopic data. Using Keeling plot analysis on instrumental records and historical reconstructions, the study finds a stable carbon isotope intercept (𝛿13C𝐼) of approximately -13.2 ‰ dating back to 1500 AD.

Because the 𝛿13C ratio [Carbon-13 Isotope Ratio] has remained unchanged over five centuries — despite a massive 10,000-fold increase in human-caused emissions — human activity cannot be the primary driver of atmospheric CO2 changes. Thus, the fossil fraction of the net carbon addition to the atmosphere, f, effectively equates to zero (f ≈ 0).

“The five-century invariance of 𝛿13C across a roughly 10⁴-fold increase in fossil emissions further collapses the admissible band to f ≈ 0.”

By applying a standard two-endmember mixture equation to this data, the authors demonstrate that the fossil-fuel fraction of the net carbon addition is strictly constrained to a maximum of 26%, and more likely the fraction is close to zero given the five-century invariance.

“If f ≈ 0, then the anthropogenic contribution to the net atmospheric CO2 addition is approximately zero…”

The authors’ conclusion about the lack of anthropogenic signature detected in the rising CO2 concentration is derived from IPCC-endorsed data and rests on mathematical certainties. Thus, critics cannot dismiss it without explicitly rejecting foundational principles of arithmetic and mass conservation, standard isotopic values, or the primary measurement datasets themselves.

Image Source: Cohler and Soon, 2026