Radiocarbon and the global environment: natural variability and the human influence

Over the last 50,000 years, atmospheric 14C changes can be reconstructed from the difference between 14C and calendar ages. The two main causes responsible for the observed changes in atmospheric 14C are the modulation of the 14C production rate by the geomagnetic field and the modification of the carbon-14 oceanic budget by climatic changes. Atmospheric 14C was higher by a factor of 2 at the onset of the upper Paleolithic. Variations of similar amplitude were recorded in the 50's and early 60's, following the atmospheric detonation of nuclear bombs. The cumulative contribution of nuclear industry from its start to now is of the order of 1/100 of the bomb 14C inventory. Representing annually 14% of the 14C natural production rate, this contribution to the 14C/12C isotopic ratio is presently counterbalanced by the dilution effect of the fossil CO2 emissions (Suess effect). (authors)