The background of energy and renewable energy is presented. Next the Green Agenda and energy, Energiewende is discussed in detail. In this regard, electricity carbon dioxide emissions and costs in various countries, e.g. Germany in pre- and post-reunification, are analysed. In the following, nuclear energy and electricity generation are discussed, also presenting the worldwide temporal variation of nuclear reactors operating and their net capacity. Based on recorded nuclear accidents and nuclear waste management, an extended discussion is made on radioactive environmental contamination from nuclear energy. In this context, the rational use of nuclear energy is discussed in detail. Finally, an exploration is presented on the potential of decarbonisation in the global energy system and energy resources and the environment, providing information on global energy production from various fuels and the world energy consumption by energy source.