Limitations

    In the period of about 1700-1950 AD, the number of rapid fluctuations of ¹⁴C content due to solar activity, and also due to the addition of a lot of "dead" carbon dioxide to the atmosphere by burning of fossil fuels, makes precise calibrated ages in this region impossible. Sometimes, some regions can be excluded, but in general the entire range is quoted as the calibrated age. This region has sometimes been called the "Stradivarius gap" to illustrate the limitations of radiocarbon dating.

    After 1950, an additional source of ¹⁴C has been added to this complicated picture. Because of contamination of the atmosphere by atmosphere nuclear weapons tests between 1950 and 1963, periods after 1950 AD are characterized by higher than "modern" levels of ¹⁴C (see, for example, Levin and Kromer [1997]). Figure 3 shows the changes in the ¹⁴C content of the post-1950 atmosphere. This amount of ¹⁴C can be used to "date" an object to a specific time period in the last ~50 years. This spike reached its peak in 1963-4 at about twice the natural level. Since the Atmospheric Test Ban Treaty was signed in 1963, atmospheric ¹⁴C has declined, due to mixing with the oceans, to about 110% of "modern" in 1997.

Figure 3. Increase of carbon-14 in the atmosphere due to
atmospheric nuclear weapons testing in the period 1950-1963 AD.
Subsequently, the level has declined to about 110% of the
pre-bomb level, due to re-equilibration with the ocean.