The set of constraining assumptions retained pertain to: • UN estimates of regional demographic evolution, up to 2100 [6], which appear as the main factor in the demand (table 1); • Fossil-fuel and renewable resource estimates based on the World Energy Conference publications [7] and our previously cited analyses [8], • The strong connection between the energy system and the environment which induces external constraints on the structure of world energy supplies. The NOE scenario assumes a sustained effort focussed on energy conservation and diversification of energy resources. In particular, emphasis is placed on the use of renewable energy resources, instead of fossil-fuel resources. Environmental constraints lead to the following decisions: • Reduction of fossil fuel induced CO2 emissions to levels lower or equal to the biosphere's maximal capacity of absorption, by the year 2100. For emissions at the end of the cycle, we use the value of three gigatons of carbon [9] as the annual limit. This is a temporary value thought by many scientists to be the limit beyond which oceans are no longer capable of reabsorbing the excess of CO2 in the form of carbonate. • The halt of all nuclear fission energy production by 2100. In fact, this constraint involves the halt of all construction of new reactors after the year 2070.
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