This topic is led by the Japan Agency for Marine-Earth Science and Technology, focusing on the three major GHGs (CO₂, CH₄, N₂O) that have global impact. Through analysis using various models, we aim to understand GHG variation mechanisms while improving the accuracy of emission/absorption estimates and prediction models. Sub-theme (1) analyzes long-term variations in GHG cycles, including gas exchange with land and sea, using an 'Earth System Model' that simulates the Earth's climate and material cycles (from GHG emissions/absorption to transport and climate feedback). Sub-theme (2) simulates atmospheric GHG transport and chemical reactions using atmospheric transport models and global observational information to globally estimate GHG emissions and absorption at the surface. The Earth System Model (MIROC-ESM) used here also contributes to future climate change predictions published in IPCC reports, and collaboration between the two sub-themes will lead to improved accuracy of this prediction model.