C-14 Dating Results Calibrations of radiocarbon age determinations are applied to convert BP results to calendar years. The shortterm difference between the two is caused by fluctuations in the heliomagnetic modulation of the galactic cosmic radiation and, recently, large scale burning of fossil fuels and nuclear devices testing.
Geomagnetic variations are the probable cause of longer term differences.
The parameters for older samples, up to about 20,000 BP, as well as for all marine samples, have been inferred from other evidence. Good calibrations are presently provided for samples to about 10,000 BP . From 10,000 to 20,000 BP approximate calibrations are possible, but subject to change in the future. A Simplified Approach to Calibrating C14 Dates. It is always important to quote the data source and mathematics with your interpretations.