If the Yedoma thaws, will we notice? Quantifying detection limits of top-down methane monitoring infrastructures

Abstract. Large quantities of carbon are stored in Yedoma permafrost. When temperatures rise, its high ice content is a catalyst for rapid degradation, which in turn may cause the release of large quantities of carbon. 40 % to 70 % of the radiative forcing from this release is expected to be in the form of CH4. In this observing system simulation experiment, we examined the capabilities of three atmospheric GHG monitoring platforms i.e. tall towers, and the TROPOMI and MERLIN satellite instruments, to detect changes in CH4 release from increased Yedoma thaw. A set of environments are simulated with the GEOS-5 model: one representing a “natural” emission case as the reference, a second featuring enhanced CH4 release from Yedoma soils. From within these modelled environments, synthetic measurements are generated following best in situ practices and realistic error characterizations. For the satellites we find the lowest detection limits when aggregating measurements over a 112 d period, at Yedoma fluxes of 144 % to 367 % of current conditions. These factors are up to 1.2 times higher when taking transport modelling uncertainties into account. The tall tower network shows a wide range of detection lower limits, the lowest at only 107 % of current fluxes, but has considerably higher lower detection limits when factoring in transport modelling errors. Overall, the individual systems appear to lack the ability to detect and attribute small changes in Yedoma CH4 fluxes, and would either need to be used in combination or require a considerable time to detect changes under higher emission scenarios.