World energy supply up to the year 2100 has been analysed from a life cycle standpoint of the full fuel cycle. Five scenarios are set up and these scenarios are analysed and compared with regard to excess energy requirements, carbon emissions, health risks and investment costs for entire power generation systems. The current trend (fossil fuel-intensive) scenario of these scenarios is attractive from an investment standpoint, but deleterious froman environmental and risk standpoint, The CO2 removal and carbon recycle scenarios must get over the hard barriers of reducing excess energy use and investment costs through future technological innovations. Renewable energy technologies are environmentally appropriate and the renewable-intensive scenario could be introduced with acceptable cost burdens in long-term projections. The nuclear-intensive scenario is attractive from its economic, environmental and risk aspects, but must make efforts to acquire public and political acceptability for further worldwide adoption.