Tracing sources of atmospheric methane using clumped isotopes

With an approximately ten-year lifetime and strong infrared absorption, methane is one of the most important greenhouse gases and a target for mitigation. Here, we describe unique measurements of rare isotopic variants of methane (isotopologues, in particular, (CH3D)-C-13 and (CH2D2)-C-12) in air, which when used in combination with traditional isotope and concentration constraints, add valuable new information about the balance of atmospheric CH4 sources. Importantly, information from these isotopologue analyses distinguishes between different proposed histories of fossil fuel to microbial methane emissions, even when the traditional isotope and concentration records are the same. Consideration of these isotopologues also supports recent assertions that increases in microbial emissions are driving the most recent rise in atmospheric methane.