The goal of this theme is to evaluate national, regional, and global budgets of GHGs and other climate-relevant substances by estimating and aggregating emission and absorption fluxes of individual substances at the Earth’s surface. Unlike the top-down approach of Themes 1 and 2 that estimate surface fluxes based on observational atmospheric data, Theme 3 adopts a bottom-up approach that aggregates ground-based data of individual sources and sinks. Through the collection of detailed and highly accurate information, the bottom-up approach enables estimation of spatial distributions and breakdowns of emissions, which is difficult to do through top-down analyses. The theme comprises the following three sub-themes: (1) assessment based on models of natural emissions and removals together with anthropogenic emission inventories (University of Tokyo and Institute of Applied Energy); (2) evaluation of the magnitudes and changes in surface emissions based on satellite observational data (Chiba University); and (3) observation and model-based evaluation of CO₂ and CH₄ emissions and removals by forest soil (Forestry and Forest Products Research Institute).