Soil microbial CH₄ consumption as the second largest sink to the atmospheric CH₄ behind hydroxyl radical oxidation plays an important role in reducing its tropospheric burden. Conventional knowledge is that methanotrophs consume CH₄ in upland soils that are rich in organic matter (1, 2). The size of this removal from the atmosphere is around 40 million tons per year (3, 4), and it has doubled in the 20th century and will double again by the end of the 21st century (4). The large uncertainty of these quantifications can be constrained by a) using spatially and temporally explicit satellite soil moisture data (e.g., SMAP), b) incorporation of new discoveries on methanotrophs (e.g., high-affinity methanotrophs, HAM) into existing biogeochemistry models (5), c) using increasingly available CH₄ consumption data (1) to constrain model parameters, and d) using the remotely sensed atmospheric CH₄ data and atmospheric transport and inversion modeling (3, 5).

This project will update the assessment of global soil CH₄ sink capacity and its uncertainties using the state-of-the-art soil CH₄ biogeochemistry and atmospheric transport and inversion modeling. The assessment will be provided for the period of 2016-2024 that has quality satellite data of soil moisture and atmospheric CH₄ concentration. The uncertainty information will be derived from uncertain model algorithms, parameterization, and forcing data.

A set of hierarchical biogeochemistry models incorporated with different levels of understanding of microbial processes and controls will be driven with various forcings. The estimated soil sinks will be fed to atmospheric inversion models as a prior to invert the sink as a posterior based on satellite retrieval data of atmospheric CH₄ concentration and in situ flask measurements. The inverted sink and atmospheric concentrations will be compared with biogeochemistry model estimates and satellite and in situ concentration data.

Spatially and temporally explicit assessment of the global soil CH₄ sink and the developed modeling tools will significantly help the concerted global efforts to increase soil CH₄ sink and reduce its atmospheric concentrations and facilitate the global CH₄ cycle studies in several fronts:

1. The study will provide a benchmark of the global soil sink capacity with the state-of-the-art understanding of soil CH₄ sink processes and controls;
2. The study will guide in situ and satellite and remote sensing observations of CH₄ sink and source fluxes to accurately project its future sink and source strengths;

The findings will help enhance soil CH₄ sink and reduce its emissions at country and global scales.