A Global Methane Observation System to Reduce Uncertainty for Anthropogenic and Natural Sources and Sinks for Detecting and Attributing Climate Feedbacks.

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.