Primary energy needs and greenhouse effect increase: what can be done?

Primary energy needs are estimated to grow by a factor of 2.3 from now to 2050. At the same time, the necessary reduction of CO2 emissions may lead to a drastic cut in the use of fossil fuels. To avoid an energy shortage, a very large share of energy production has to be met by renewable energies or nuclear energy. These two kinds of energy have specific environmental impacts and constraints which are briefly discussed. A significant contribution of renewable energies implies that large land areas and a good energy storage technology are available while nuclear energy cannot be sufficiently extended using the present PWR reactor technology. Using an optimised new option for energy production, it is shown that nuclear energy can provide a significant share of energy needs. But we point out that it is no longer the time to discuss which energy has to be developed but to develop both at the appropriate significantly increased production level.