A change to U.S. GHGRP requirements for landfills in 2016 may mostly explain the substantial disagreement between TD estimates of emissions and GHGRP self-reported rates in Figure generally . Two methods are used to estimate CH4 emissions from U.S. landfills with gas capture systems, which account for the majority (~75%) of landfills and waste emissions reporting to the U.S. GHGRP: first-order decay (FOD) and collection efficiency assumption (CEA, . Operators of landfills with gas collection systems may choose which estimate they report to the GHRGP annually. Most are opting to report estimates derived with the CEA method, which consistently estimates lower emissions than the FOD method . Latitude in the method used for landfill CH4 emissions reporting may be unique to the U.S. ; to our knowledge, the FOD method is followed in Canada to estimate and report landfill emissions rates which are submitted annually to the Intergovernmental Panel on Climate Change (IPCC, . Reporting favoring the CEA method has produced a misleading trend that CH4 emissions from landfills in the U.S. are decreasing; actual emissions are likely higher and may be trending upwards in response to increasing waste deposition. We refer readers to for a detailed overview of these estimation methods for GHGRP reporting and trends in reported U.S. landfill CH4 emissions. Results from the studies suggest that key issues with the CEA method are overestimates of gas collection system efficiencies by landfill operators and higher assumed soil oxidation rates relative to the FOD method. More CH4 emissions are likely being emitted diffusely through the landfill surface, cover gaps, or other associated infrastructure than anticipated.