Fossil fuel burning weakens carbon dating methods

Growing carbon emissions can throw a spanner in the works for dating techniques used in archaeology and forensics. If emissions continue to rise, radiocarbon dating will not be able to provide definitive ages for samples ranging up to 2,000 years.

Carbon released into the air by burning fossil fuels ends up diluting the radioactive isotope of carbon used to date organisms and objects, says a study done by Imperial College, London.

By 2050, humans and organisms will have the same 'carbon age' as their ancestors from a thousand years ago.

The decades-old radiocarbon dating method measures radioactive carbon-14 in samples studied.

This isotope is produced in the atmosphere when cosmic rays convert nitrogen-14 into C-14.
It is then absorbed by plants through photosynthesis. When eaten by animals the carbon-14 becomes a useful age reckoner.

As it decays over time, leaving behind stable carbon atoms the C-14 allows scientists to compare the ratio of stable to radioactive carbon atoms and determine a sample's age.

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.

Physicist Heather Graven of Imperial College looked at how atmospheric C-14 will change over the 21st century under varying emission scenarios.

Under aggressive reduction by 2020, atmospheric C-14 will decline to pre-industrial concentrations and stay flat over the 21st century. That would limit carbon age similarity to 100 years.

On the other hand under a rising emission scenario, levels of C-14 will fall below pre-industrial levels and life forms will 'age' faster. By the end of the century, new products and 2,000-year-old items will show the same age.

At current rates of emissions, by 2050 a new T-shirt would have the same radiocarbon date as a robe worn by William the Conqueror a thousand years earlier.

The study has been published in the Proceedings Of The National Academies Of Sciences.

The CO2 levels in the atmosphere have raced from 280ppm (parts per million) in 1800 to 290ppm in 1900 and crossed the 400ppm mark this year.

Net global emissions of carbon must drop 40-70% by 2050, hitting zero by the end of the century, the IPCC has said if the planet is to avoid a catastrophic temperature rise beyond 2C.