Researchers from the Oeschger Centre for Climate Change Research have disproven the hotly debated hypothesis that humans measurably influenced atmospheric concentrations of CO2 as early as during the stone age. The prestigious science magazine Naturehas published the results of the study, which was conducted together with the Alfred Wegener Institute for Polar and Marine Research based in Bremerhaven, Germany. For the first time, the scientists were able to perform carbon isotope (C-13) measurements on air trapped in an Antarctic ice core with a precision that permitted a quantification of the mechanisms responsible for the CO2 changes in the past 11,000 years.
This evidence renders untenable the hypothesis that agricultural activity by humans was responsible for a sudden change in the atmospheric CO2 trend 6,500 years ago. The hypothesis claimed that humans influenced the climate long before the industrial revolution and the steep rise in CO2 caused by the use of fossil fuels. The measurements show a clear increase of the carbon isotope C-13 along with a slight decrease of CO2, between 11,000 and 6'500 years ago. This is an indication of the growth of the biosphere: the uptake of carbon through the expansion of ecosystems after the end of the last ice age. By contrast, the subsequent increase of CO2 concentrations has led to no clear change in the concentration of C-13 which suggests ocean processes as a possible cause.
If humans had been responsible for the increase of CO2 in the atmosphere 6,500 years ago through a large-scale clearing of land, the share of C-13 would have clearly diminished since then, as model simulations demonstrate. However, the newest measurements show an increase, rather than a decrease. Therefore, the global influence of humans on CO2 levels in the atmosphere only began during the industrial revolution.
