Satellite Constraints on European Landfill Methane Emissions Reveal Underestimation in Reported Inventories

Abstract. This study evaluates the consistency between landfill methane emissions reported in European Union bottom-up inventories—the European Pollutant Release and Transfer Register (E-PRTR) and the Industrial Emissions Directive (IED)—and independent satellite-derived estimates compiled by the United Nations Environment Programme’s International Methane Emissions Observatory (IMEO). Additional emission estimates from GHGSat observations are included to extend the satellite-based assessment. Our study reveals that satellite detections remain limited, with cloud cover representing a major observational constraint, and primarily capture a subset of the largest emitters, preventing comprehensive characterization of landfill methane emissions across Europe. Among the datasets considered, GHGSat provides comparatively better spatial coverage and improved capability for detecting moderate emitters. The comparison between European Union inventory data and satellite-derived observations reveals a systematic underestimation of landfill methane emissions in bottom-up inventories. Measurements from NASA's high-resolution Earth Surface Mineral Dust Source Investigation (EMIT) instrument indicate methane emission rates that exceed reported inventory values by up to one order of magnitude. Additionally, satellite observations reveal pronounced seasonal variability in landfill emissions that is not captured by annual inventory reporting. Although the available observations cannot establish whether this bias is representative of the entire European landfill sector, if confirmed across a larger and representative sample of facilities, such systematic underestimation could indicate that the European anthropogenic methane budget is significantly underestimated. These findings highlight the need to integrate facility-level reporting with satellite observations to better constrain landfill methane emissions, improve emission verification, and support the assessment of progress toward EU methane-mitigation and climate-neutrality targets.