The Suess effect is a change in the ratio of the atmospheric concentrations of heavy isotopes of carbon (13C and 14C) by the admixture of large amounts of fossil-fuel derived CO2, which contains no 14CO2 and is depleted in 13CO2 relative to CO2 in the atmosphere and carbon in the upper ocean and the terrestrial biosphere .
[1] It was discovered by and is named for the Austrian chemist Hans Suess,[2] who noted the influence of this effect on the accuracy of radiocarbon dating.
This effect is the basis of radiocarbon dating, with the proviso that mass-dependent fractionation and the decrease in 14C due to radioactive decay and are accounted for.
In addition, most fossil fuels originate from C3 biological material produced tens to hundreds of millions of years ago.
Fossil fuels such as coal and oil are made primarily of plant material that was deposited millions of years ago.