Image copyright SPL Image caption Radiocarbon dating was used to determine the true age of the Shroud of Turin

Growing emissions from the burning of fossil fuels are threatening the effectiveness of radiocarbon dating, according to new research.

The dating method has been used for decades to accurately determine the age of a wide range of artefacts.

But using fossil fuels pumps a type of carbon into the atmosphere that confuses the dating technique.

Scientists say that by 2050, new clothes could have the same radiocarbon date as items 1,000 years old.

Developed in the late 1940s, the method measures carbon-14, a radioactive form of the element. It's produced in the atmosphere and then absorbed by plants through photosynthesis.

Animals that eat the plants ingest the carbon-14. Scientists are able to work out the age of almost anything organic by comparing the level of carbon-14 to non-radioactive carbon in the sample.

The method has been used to accurately determine the ages of thousands of artefacts and to uncover art fraud.

Perhaps the most famous case where radiocarbon dating was used was in the investigation of the Shroud of Turin, which scientists in 1988 determined had originated in the 13th century, more than 1,200 years after the death of Christ - whose image it is supposed to represent.

Bad dates

However, the use of carbon based fossil fuels such as coal and oil since the industrial revolution have increased the amount of non-radioactive carbon in the atmosphere. As the emissions grow, so does the diluting effect on carbon-14 and the accuracy of the ageing technique is lost.

"As carbon-14 decays over time the fraction will decrease so that's how we use it for dating," the paper's author Dr Heather Graven told BBC News.

"But we can also change this ratio of radioactive carbon to total carbon, if we are adding non-radioactive carbon and that's what's happening with fossil fuels, we get this dilution effect."

The study looked at the likely carbon emissions pathways over the next century and suggested that the increases in non-radioactive carbon by 2020 could start to impact the dating technique.

"If we did any current measurements on new products, they will end up having the same fraction of radiocarbon to total carbon as something that's lost it over time due to decay," said Dr Graven.

"So if we just measure the fraction they'll look like they have the same age for radiocarbon dating."

At current rates of emissions increase, according to the research, a new piece of clothing in 2050 would have the same carbon date as a robe worn by William the Conqueror 1,000 years earlier.

"It really depends on how much emissions increase or decrease over the next century, in terms of how strong this dilution effect gets," said Dr Graven.

"If we reduce emissions rapidly we might stay around a carbon age of 100 years in the atmosphere but if we strongly increase emissions we could get to an age of 1,000 years by 2050 and around 2,000 years by 2100."

The research has been published in the journal, Proceedings of the National Academy of Sciences.

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