The variation is certainly partially the result of a change in the cosmic ray production rate of radiocarbon.
The cosmic-ray flux, and hence the production rate of C-14, is a function not only of the solar activity but also of the magnetic dipole moment of the Earth.4Though complex, this history of the earth’s magnetic field agrees with Barnes’ basic hypothesis, that the field has always freely decayed....
There are two main applications for radiometric dating.
Many people have been led to believe that radiometric dating methods have proved the earth to be billions of years old.
The procedures used are not necessarily in question. The secular (evolutionary) worldview interprets the universe and world to be billions of years old. The use of carbon-14 dating is often misunderstood.
Carbon-14 is mostly used to date once-living things (organic material). Carbon-14 is constantly being added to the atmosphere.
The earth has a magnetic field around it which helps protect us from harmful radiation from outer space. The stronger the field is around the earth, the fewer the number of cosmic rays that are able to reach the atmosphere.
This would result in a smaller production of The cause for the long term variation of the C-14 level is not known.