Impact of fossil fuel emissions on atmospheric radiocarbon and various applications of radiocarbon over this century

Abstract

Radiocarbon analyses are commonly used in a broad range of fields, including earth science, archaeology, forgery detection, isotope forensics, and physiology. Many applications are sensitive to the radiocarbon (14C) content of atmospheric CO2, which has varied since 1890 as a result of nuclear weapons testing, fossil fuel emissions, and CO2 cycling between atmospheric, oceanic, and terrestrial carbon reservoirs. Over this century, the ratio 14C/C in atmospheric CO2 (Δ14CO2) will be determined by the amount of fossil fuel combustion, which decreases Δ14CO2 because fossil fuels have lost all 14C from radioactive decay. Simulations of Δ14CO2 using the emission scenarios from the Intergovernmental Panel on Climate Change Fifth Assessment Report, the Representative Concentration Pathways, indicate that ambitious emission reductions could sustain Δ14CO2 near the preindustrial level of 0‰ through 2100, whereas “business-as-usual” emissions will reduce Δ14CO2 to −250‰, equivalent to the depletion expected from over 2,000 y of radioactive decay. Given current emissions trends, fossil fuel emission-driven artificial “aging” of the atmosphere is likely to occur much faster and with a larger magnitude than previously expected. This finding has strong and as yet unrecognized 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 y old.

C4MIP – The Coupled Climate–Carbon Cycle Model Intercomparison Project: experimental protocol for CMIP6

“…The atmospheric forcing data sets will be available at the C4MIP website. We also plan to make available atmospheric forcing data for carbon isotopes for the ssp585 scenario and for other scenarios and extensions using a simple carbon cycle model, following Graven (2015).…”

Compiled records of carbon isotopes in atmospheric CO<sub>2</sub> for historical simulations in CMIP6

“…Carbon isotopes will also be included in the simulation of future scenarios. In a separate paper, we will provide atmospheric 14 C and δ 13 C for future scenarios in CMIP6 created with a simple carbon cycle model (Graven, 2015) and CO 2 emission and concentration scenarios from ScenarioMIP (O'Neill et al, 2016).…”

“…This adjustment takes into account that 14 C observed at Macquarie Island is lower than the stations further north and south, resulting from gas exchange over the Southern Ocean . Macquarie Island data are available for 1993. For 2015 Neumayer data were available, so the annual mean at Neumayer was adjusted by −2 ‰, which is the mean difference between Neumayer and the calculated Southern Hemisphere average for 2010-14.…”

Radiocarbon analysis of stratospheric CO<sub>2</sub> retrieved from AirCore sampling

“…Figure 6b shows the measured radiocarbon concentration in the extracted CO 2 samples, with orange triangles representing samples from 15 July 2014 and cyan circles representing samples from 16 July 2014. The present 14 C value for tropospheric CO 2 is ≈ 20 ‰ (Levin et al, 2013;Graven, 2015;Hua et al, 2013). The uncertainties in the 14 C values, shown in Fig.…”