By the time a halt was called to aboveground nuclear testing in 1963, levels of carbon-14 in the atmosphere had doubled beyond natural background levels, says Frisén. By taking this into account, one can see detectable changes in levels of carbon-14 in modern DNA, he says.
"Most molecules of the cell will turn over all the time.
So detecting the subtle change in the ratio of normal to naturally occurring radioactive carbon over just a few years is incredibly hard.
But Jonas Frisén of the Karolinska Institute in Stockholm, Sweden, says it can be done if one takes advantage of the signal left by nuclear testing, which spewed high levels of carbon-14 into the air during the Cold War.
Radiocarbon dating, which is used to calculate the age of certain organic materials, has been found to be unreliable, and sometimes wildly so - a discovery that could upset previous studies on climate change, scientists from China and Germany said in a new paper.