Methane mitigation, especially in the near-term, is critical for meeting global climate goals. The U.S. and China, as two of the largest global methane emitters, will play a significant role in global mitigation efforts through national methane emissions reduction, as well as by collaborating on key methane topics, as outlined in recent joint statements issued by both countries. Current methane emission estimates are highly uncertain, given that methane emission factors (i.e. the emissions intensity of different activities) are highly dependent on local conditions. This analysis evaluated around 50 estimates of methane emissions in the U.S. and China across all major sectors to identify areas of uncertainty and highlight opportunities for cross-country collaboration. Shared sources of emissions with high uncertainty include waste and livestock emissions, as well as abandoned fossil production sites (coal mines and oil wells), which present opportunities for knowledge sharing and joint leadership. Key areas for collaboration include improving data collection, monitoring and availability to develop more detailed emission factors that take into account local conditions and temporal sources of emissions. The U.S. and China can jointly collaborate on developing a transparent, multi-scale approach to emissions inventory development and mechanism for integrating multiple methodologies into national emissions estimates, to improve accuracy of emissions estimates and better inform mitigation strategies and policy discussions.

International frameworks for climate mitigation that build from national actions have been developed under the United National Framework Convention on Climate Change and advanced most recently through the Paris Climate Agreement. In parallel, sub-national actors have set greenhouse gas (GHG) reduction goals and developed corresponding climate mitigation plans. Within the U.S., multi-state coalitions have formed to facilitate coordination of related science and policy. Here, utilizing the forum of the NASA Carbon Monitoring System’s Multi-State Working Group (MSWG), we collected and reviewed climate mitigation plans for 11 states in the Regional Greenhouse Gas Initiative (RGGI) region of the Eastern U.S. For each state we reviewed the 1) policy framework for climate mitigation, 2) GHG reduction goals, 3) inclusion of forest carbon in the state’s climate action plan, 4) existing science used to estimate forest carbon, and 5) stated needs for carbon monitoring science. Across the region, we found important differences across all categories. While all states have GHG reduction goals and framework documents, nearly three-quarters of all states do not account for forest carbon when planning GHG reductions; those that do account for forest carbon use a variety of scientific methods with various levels of planning detail and guidance. We suggest that a common, efficient, standardized forest carbon monitoring system would provide important benefits to states and the geographic region as a whole. In addition, such a system would allow for more effective transparency and progress tracking to support state, national, and international efforts to increase ambition and implementation of climate goals.