Coal, petroleum, and natural gas supplied 81.5% of global primary energy in 2023, a dependence created over two centuries of industrialisation that has enabled unprecedented economic growth while imposing substantial environmental costs. This chapter examines fossil-fuel chemistry, formation, extraction, refining, and combustion; evaluates impacts from air pollution and climate forcing to water contamination and ecological damage; and considers the external costs that are not fully reflected in market prices. Global energy-related emissions exceeded 40 Gt CO₂-equivalent for the first time in 2023. Understanding both the functional advantages of fossil fuels—high energy density, storability, dispatchability, and infrastructure compatibility—and their environmental and public-health costs is essential for evaluating energy-transition alternatives (Energy Institute, 2024).
Keywords:fossil fuels, combustion emissions, air pollution, climate change, external costs, energy transition