Long-term and interannual variations of atmospheric methane observed by the NIES and collaborative observation networks

Abstract

Effective action for climate change mitigation requires an accurate understanding of global greenhouse gas budgets, including those of methane (CH4). Atmospheric measurement data provide key constraints for estimating the magnitudes and distributions of sources and sinks and are utilized in atmospheric chemistry transport modeling studies. Long-term atmospheric measurement networks have revealed decadal, interannual, and seasonal variations in atmospheric CH4. In 2020, a record-breaking annual CH4 increase was recorded, but its cause is still unknown. This study analyzes atmospheric CH4 variations using data from the National Institute for Environmental Studies (NIES) and its collaborative observation networks. Datasets from ground, mobile, and satellite platforms, employing diverse measurement techniques, confirmed past episodes, recent remarkable increases, and spatial distributions of atmospheric CH4. Our data clearly showed a sustained CH4 increase from 2020 to 2022, with the highest annual increase in 2021. The atmospheric CH4 increase was pronounced in the northern mid-to-high latitudes in 2020, but the enhancement shifted south in 2021 and 2022. This study demonstrates the capability of observational data from the NIES and collaborative networks in accurately characterizing spatiotemporal variations in atmospheric CH4 regularly, supporting the improvement of our estimates of the global CH4 budget. (Figure presented.)