Lawrence Berkeley National Laboratory

Atmospheric methane (CH₄) concentrations are accelerating global warming as net emissions increase. Observing systems that quantify sources remain too sparse and fragmented to detect trends-especially in remote regions where climate-driven natural emissions may be rising. We provide a framework for quantifying uncertainty reductions through the implementation of a global ecosystem-methane observing system designed to: (i) substantially lower uncertainty in sectoral and regional emissions, (ii) separate co-occurring anthropogenic and natural fluxes, and (iii) trend detection at regional scales to verify mitigation progress and provide early warning of natural feedbacks. Using bottom-up inventories and process-model ensembles for 2014-2023, we show that anthropogenic emissions remain uncertain by ∼32% globally, while natural sources-tropical and boreal-arctic wetlands, fires, and inland waters-carry far larger uncertainties (+ 70%) and trend uncertainties reaching ∼200%. Additional observations must match spatial emission structure to increase observability of emissions: high-resolution satellite constellations for point sources combined with expanded flux networks and wetland mapping for diffuse sources, and denser ground-based atmospheric column measurements to restore observability in under-sampled tropics and high latitudes. Notional analyses indicate that targeted additions of flux towers and ∼20 in situ atmospheric column concentration instruments per key tropical region could reduce continental-scale uncertainties at modest cost.