Understanding, quantifying, and tracking atmospheric methane and emissions is essential for addressing concerns and informing decisions that affect the climate, economy, and human health and safety. Atmospheric methane is a potent greenhouse gas (GHG) that contributes to global warming. While carbon dioxide is by far the dominant cause of the rise in global average temperatures, methane also plays a significant role because it absorbs more energy per unit mass than carbon dioxide does, giving it a disproportionately large effect on global radiative forcing. In addition to contributing to climate change, methane also affects human health as a precursor to ozone pollution in the lower atmosphere. Improving Characterization of Anthropogenic Methane Emissions in the United States summarizes the current state of understanding of methane emissions sources and the measurement approaches and evaluates opportunities for methodological and inventory development improvements. This report will inform future research agendas of various U.S. agencies, including NOAA, the EPA, the DOE, NASA, the U.S. Department of Agriculture (USDA), and the National Science Foundation (NSF). Table of Contents Front Matter Summary 1 Introduction 2 Current Inventories of Methane Emissions 3 Methane Emission Measurement and Monitoring Methods 4 Addressing Uncertainties in Anthropogenic Methane Emissions 5 Presenting Methane Emission Data and Results 6 Meeting the Challenges of Characterizing Methane Emissions References Glossary Appendix A: Acronyms and Abbreviations Appendix B: Definition of U.S. Greenhouse Gas Inventory Categories Appendix C: Other Anthropogenic Sources of Methane Appendix D: U.S. Greenhouse Gas Inventory Development Appendix E: Acknowledgment of Those Who Provided Input to the Committee Appendix F: Common Units for Reporting Methane Concentrations and Emissions Appendix G: Biographical Sketches of Committee Members Appendix H: Disclosure of Conflict of Interest