The change in the ratios of carbon isotopes (specifically, the 14 C: 12 C and 13 C: 12 C ratios) caused by release of carbon from fossil fuels. Such materials essentially lack any 14C, because, during their burial underground, 14C decays radioactively to 14N (nitrogen-14). They are also strongly depleted in 13C because of the preferential uptake of 12C, relative to 13C, by the original bacteria and plants from which fossil fuels later formed. Burning the fuels produces carbon dioxide, whose carbon consists almost entirely of the 12C isotope, and thus subsequently dilutes the ratios in all carbon reservoirs. See also carbon cycle; carbon dating.
Subjects: Meteorology and Climatology.