The energy-efficiency lever wins unanimous support since it means consuming less for the provision of an equal service. The laws of physics and the recent history of technological advances show that this necessary lever will not be sufficient. Energy sobriety is far more complex to develop as it implies considerable lifestyle and changes in the way society is organized. Energy consumption has allowed for the replacement of humans by machines and a tertiarization of economy. Before long, a shortage in fossil energy sources will necessarily occur, and renewable or nuclear energy will not make up for their replacement. Policy makers have three possibilities for the decades to come: consuming much less energy, developing nuclear energy, and carrying on exploiting fossil energy sources – particularly coal, non-conventional oils and shale gas – since resources exist, thereby increasing pollution and global warming with such consequences as respiratory diseases, floods, storms.