The global carbon dioxide (CO 2 ) flux from subaerial volcanoes remains poorly quantified, limiting our understanding of the deep carbon cycle during geologic time and in modern Earth. Past attempts to extrapolate the global volcanic CO 2 flux have been biased by observations being available for a relatively small number of accessible volcanoes. Here, we propose that the strong, but yet unmeasured, CO 2 emissions from several remote degassing volcanoes worldwide can be predicted using regional/global relationships between the CO 2 /S T ratio of volcanic gases and whole-rock trace element compositions (e.g., Ba/La). From these globally linked gas/rock compositions, we predict the CO 2 /S T gas ratio of 34 top-degassing remote volcanoes with no available gas measurements. By scaling to volcanic SO 2 fluxes from a global catalogue, we estimate a cumulative “unmeasured” CO 2 output of 11.4 ± 1.1 Mt/yr (or 0.26 ± 0.02·10 12 mol/yr). In combination with the measured CO 2 output of 27.4 ± 3.6 Mt/yr (or 0.62 ± 0.08·10 12 mol/yr), our results constrain the time-averaged (2005–2015) cumulative CO 2 flux from the Earth’s 91 most actively degassing subaerial volcanoes at 38.7 ± 2.9 Mt/yr (or 0.88 ± 0.06·10 12 mol/yr).

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