"Global climate change induced by anthropogenic emissions of CO2 is currently a major issue facing humanity, but uncertainties in the magnitude and rate of climate change remain, and deterministic predictions are beyond our capacity. In this context, the study of how the geochemical carbon cycle established a relatively narrow band of variability in atmospheric CO2 concentrations over the last 400 ka is of great interest. However, large uncertainties in both weathering and volcanic CO2 fluxes prevent a truly quantitative assessment of this critical cycle. Measuring the global volcanic CO2 flux, GVFCO2, would allow us to better understand the likely impact large eruptions have had in Earth’s history, and constrain the natural vs. anthropogenic CO2 flux.We propose a truly innovative project to address head on the problem of determining GVFCO2. We will create new, compact instruments, utilising cutting-edge laser technologies, which will allow us to measure volcanic CO2, H2O, SO2 and HCl fluxes from aircraft. By flying below and through the volcanic plumes created by ~50 active volcanoes (~10% of all active volcanoes) of the Banda-Sunda arc in Indonesia, the majority of which have never been measured before, we will dramatically increase our understanding of GVFCO2 and geochemical cycles for all these species.Measuring the volcanic emissions from an entire subduction arc is an unprecedented experiment, providing insight into the slab and mantle heterogeneity and volatile mass balance. Perhaps the most important breakthrough that we will pursue will be the determination of the 37Cl/35Cl ratio from HCl emitted from each volcano. This ratio reflects the mantle/slab source proportion, and allows the input rate of volatiles to the mantle to be measured.The application of innovative new technology we propose here will produce ground-breaking insights into volcanology, isotope and gas geochemistry, volatile cycles, subduction and climate change."