This lecture discusses historical climate emissions, focusing on big polluting nations and climate justice. It explores the responsibility of countries for climate change, analyzing emissions from 1850 to 2021. The lecture delves into the atmospheric chemical reactions involving greenhouse gases like methane, CO2, and ozone, impacting climate feedback and sensitivity. It explains the role of OH radicals as the main atmospheric oxidant and the sinks of OH in the troposphere. The lecture also covers methane oxidation, ozone formation, and the impact of CO and CH4 oxidation on ozone production. Additionally, it addresses the methane riddle, global methane emissions trends, and the atmospheric chemistry behind methane's effective radiative forcing through ozone.