Being led by the Japan Agency for Marine–Earth Science and Technology (JAMSTEC), this theme focuses on three major GHGs with global impact (CO₂, CH₄, N₂O). The Analyses utilizing different modeling approaches aim to better understand the mechanisms driving GHG variability, while also generating fine-scale estimates of the sources and sinks and improving the accuracy of models for climate projections. Sub-theme (1) employs an Earth System Model (ESM), which is capable of simulating the Earth’s climate and GHG cycles—including the emission, uptake, and transport of GHGs and their feedback to the climate system—to analyze long-term variations in the global GHG cycle, including gas exchange between the atmosphere, land, and ocean. Sub-theme (2) utilizes atmospheric chemistry-transport models combined with global observational datasets to estimate global and regional budgets of the GHGs. Given that the ESM is also used to project future climate change and has contributed to International Panel on Climate Change (IPCC) Assessment Reports, integration of these two sub-themes will assess accuracy and reliability of historical simulations and aim toward improved future projection.