evidence: Carbon isotopes, 14C and 13C, in atmospheric CO2 are changing in response to fossil fuel emissions and other human activities.[…]Emissions of CO2 from fossil fuel combustion and land use change reduce the ratio of 13C/12C in atmospheric CO2 (δ13CO2). This is because 12C is preferentially assimilated during photosynthesis and δ13C in plant-derived carbon in terrestrial ecosystems and fossil fuels is lower than atmospheric δ13CO2.[…]Cement manufacturing also involves "fossil" carbon in that the source material is geological and therefore free of any 14C.[…]Since the Industrial Revolution, the carbon isotopic composition of atmospheric CO2 has undergone dramatic changes as a result of human activities and the response of the natural carbon cycle to them. The relative amount of atmospheric 14C and 13C in CO2 has decreased because of the addition of 14C- and 13C-depleted fossil carbon. [...] - As a result of the increased CO2 concentration, the isotopic signature δ13C in the atmosphere has decreased; [...] - Human CO2 emissions have played a minor role in the recent climatic evolution, which is hardly discernible in observational data and unnecessary to invoke in modelling the observed behaviours, including the change in the isotopic signature δ13C in the atmosphere.