Perhaps it is unrealistic to try to shed light on these formidable questions. Our inability to correctly predict the economic situation ten years from now, and the unknown nature of scientific and technical discoveries, provide support for such a criticism. Nevertheless, our perspective stems from another mode of thought. The aim of providing descriptions of diversified long term scenarios is not to designate the boundaries of a predictable future or to specify the degree of certainty that we can apply with respect to this future. Rather, its goal is to emphasize the imbalances and main points of rupture. For example, we make the assumption that world population will stabilize around 11 billion inhabitants in the year 2100. Technological progress Without going into an in-depth 111 discussion of potential technological developments in the field of energy supply or that of its ultimate use in the 21 st century, we would like to stress the following points. There is significant potential for improving energy efficiency in already industrialized countries. This is also true in southern countries currently undergoing development. The history of industrialized countries, and more recently that of certain countries undergoing rapid industrialization, shows that productivity increase and energy consumption reduction are two elements in a single system of improvement [2|. (They are not opposed to each other as sometimes thought). Technological progress in the southern countries will have even greater consequences due to the rapid growth-rate of these countries. There is diversification of energy production is in two directions, first, by the simultaneous production of several energy carriers (electricity and heat for example), then by the diversification of the nature and quality of main supply sources utilized in obtaining a given amount of energy. This includes the generation of electricity from wood, waste-materials, sun, wind, and the manufacturing of fuel from biomass, coal, natural gas, electricity, etc. Within this latter context of diversification, renewable energy sources (sun. hydraulic, wind, biomass) have a great potential. In providing new solutions to energy concerns related to transportation, there are new energy vectors. These include hydrogen produced from electricity (nuclear, solar or hydraulic) and substitution fuels produced from biomass. Both cases provide new solutions to the problem posed by transportation, the importance of which is rapidly increasing world-wide. One of the major technological challenges of the 21st century resides in the bio-technological transformation of lignocellulose, and hence, in the direct transformation of wood into motor fuels.
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