Radiocarbon analyses are commonly used in a broad range of
fields, including earth science, archaeology, forgery detection,
isotope forensics, and physiology. Many applications are sensitive
to the radiocarbon (14C) content of atmospheric CO2, which has
varied since 1890 as a result of nuclear weapons testing, fossil fuel
emissions, and CO2 cycling between atmospheric, oceanic, and terrestrial
carbon reservoirs. Over this century, the ratio 14C/C in atmospheric
CO2 (Δ14CO2) will be determined by the amount of
fossil fuel combustion, which decreases Δ14CO2 because fossil fuels
have lost all 14C from radioactive decay. Simulations of Δ14CO2
using the emission scenarios from the Intergovernmental Panel
on Climate Change Fifth Assessment Report, the Representative
Concentration Pathways, indicate that ambitious emission reductions
could sustain Δ14CO2 near the preindustrial level of 0‰
through 2100, whereas “business-as-usual” emissions will reduce
Δ14CO2 to −250‰, equivalent to the depletion expected from over
2,000 y of radioactive decay. Given current emissions trends, fossil
fuel emission-driven artificial “aging” of the atmosphere is likely
to occur much faster and with a larger magnitude than previously
expected. This finding has strong and as yet unrecognized implications
for many applications of radiocarbon in various fields,
and it implies that radiocarbon dating may no longer provide definitive
ages for samples up to 2,000 y old.