Indeed, by doing almost 20 seconds of research on google (type in “variations in C14”, click on Google Scholar) the second link is this article from 1954: Carbon 13 in plants and the relationships between carbon 13 and carbon 14 variations in nature So, this issue has been known about for a long time. Then we compare the two and adjust the radiocarbon date to the known date. That’s less than 1% if you’re interested in that sort of thing. But this is already almost a thousand words and I’ve only done ONE! Long story short, scientists have always known that variations in C-14 concentration happen.
Do you honestly think that no one has done anything about it? By making thousands (if not millions) of these adjustments we get a very good idea of how old a piece of unknown material can be. The 2009 calibration set extends the ‘well calibrated range’ to 50,000 years using the varves in a Japanese lake. This is unlike the creationists which think it happened, but can’t be bothered to check.
Scientists, using rigorous methods have established a process to eliminate this problem by calibrating radiocarbon dating results to items of a known age.
In this way, items of unknown age can be tested and an age determined to a reasonable degree of accuracy. More tomorrow where we explore the concept of isochron dating and how it neatly destroys most of the rest of these ‘issues’.
When an organism dies it ceases to replenish carbon in its tissues and the decay of carbon 14 to nitrogen 14 changes the ratio of carbon 12 to carbon 14.