If you're a fan of murder mysteries or forensic detective dramas, you'll know that carbon dating is a crucial way of figuring out just how old those faded bones buried way out in the woods actually are. But a researcher in the UK has pointed out a rather large problem: because of increased levels of carbon in our atmosphere, the organic tissue attached to humans and animals is appearing to be older than it really is.

"Given current emissions trends, fossil fuel emission-driven artificial 'ageing' of the atmosphere is likely to occur much faster and with a larger magnitude than previously expected," Heather Graven from the Imperial College London writes. "This finding has strong and as yet unrecognised implications for many applications of radiocarbon in various fields, and it implies that radiocarbon dating may no longer provide definitive ages for samples up to 2,000 years old."

Graven's predictions, which were published in the Proceedings of the National Academy of Sciences, are based on the assumption that carbon emission levels will continue to rise. If they can be reined in and reduced, radiocarbon dating could still be of use.

Radiocarbon (or C-14 ) is created in the atmosphere when cosmic rays combine with nitrogen. Trace amounts of it are taken up by plants and enter the food chain, and because C-14 is a radioactive isotope, it naturally decays and leaves behind stable carbon atoms. Want to know how old a sample is? Compare the number of stable carbon atoms to the number of radioactive carbon atoms to figure out how long ago it was fossilised (upon death, a living organism stops taking in new carbon, thus dating it).

The problem is that the fossil fuels we're pouring into the atmosphere have lost all their C-14 over millions of years, changing the balance of the atmosphere and reducing C-14 levels. As living humans and animals take in less C-14, they will appear to be ageing in a radiocarbon dating sense, even though they're not yet dead. 

By 2050, she says, new clothes could have the same radiocarbon date as clothes that are 1,000 years old, if fossil fuel emissions are not checked. From dating archaeological digs to uncovering art fraud, this poses a serious challenge for forensic scientists.

"We can see from atmospheric observations that radiocarbon levels are steadily decreasing. How low they go depends on changes in our fossil fuel emissions," says Graven in a press release. "If we reduced fossil fuel emissions, it would be good news for radiocarbon dating."