Anthropogenic perturbations to atmospheric methane reflected in Greenland firn air clumped isotope measurements
- Malavika Sivan
- Jiayang Sun
- Patricia Martinerie
- Maria Elena Popa
- James Farquhar
- Maarten Krol
- Carina van der Veen
- Bibhasvata Dasgupta
- Mojhgan A. Haghnegahdar
- Camilla Marie Jensen
- Ji-Woong Yang
- Johannes Freitag
- Kévin Fourteau
- Thomas Blunier
- Thomas Röckmann
2026-07-15
The ongoing debate over the origin of rising atmospheric methane levels highlights gaps in our understanding of its global budget. To our knowledge, we present the first reconstructed clumped isotopic composition of atmospheric methane dating back to the early 1990s, based on large-volume firn air samples from the Greenland ice cap. Our measurements indicate that atmospheric ∆ 12 CH 2 D 2 around 1993 was 10 ± 2 per mil lower than in the mid-2020s, likely marking the lowest level over the last millennium. We attribute this shift to the unprecedented anthropogenic perturbation of global methane emissions during the industrial period. The temporal lag in the atmospheric isotopic signature reflects the disequilibrium effect caused by the longer atmospheric lifetime of 12 CH 2 D 2 relative to methane (CH 4 ). Moreover, our results suggest that the kinetic isotope effect in the removal of 12 CH 2 D 2 by the hydroxyl radical needs to be much smaller than previously estimated. Future changes in atmospheric ∆ 12 CH 2 D 2 will continue to reflect evolving CH 4 emission and removal pathways.