Preindustrial 14CH4 indicates greater anthropogenic fossil CH4 emissions

@article{Hmiel2020Preindustrial1I,
  title={Preindustrial 14CH4 indicates greater anthropogenic fossil CH4 emissions},
  author={Benjamin Hmiel and Vasilii V Petrenko and Michael Dyonisius and Christo Buizert and A. M. Smith and Philip F. Place and Christina M. Harth and Ross Beaudette and Quan Hua and B. Yang and Isaac Vimont and Sylvia E. Michel and Jeffrey P. Severinghaus and David M. Etheridge and Tony Bromley and Jochen Schmitt and Xavier Fa{\"i}n and Ray F. Weiss and Edward J. Dlugokencky},
  journal={Nature},
  year={2020},
  volume={578},
  pages={409 - 412}
}
Atmospheric methane (CH4) is a potent greenhouse gas, and its mole fraction has more than doubled since the preindustrial era1. Fossil fuel extraction and use are among the largest anthropogenic sources of CH4 emissions, but the precise magnitude of these contributions is a subject of debate2,3. Carbon-14 in CH4 (14CH4) can be used to distinguish between fossil (14C-free) CH4 emissions and contemporaneous biogenic sources; however, poorly constrained direct 14CH4 emissions from nuclear reactors… 
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