If electricity use continues to double every nine years, huge amounts of power will have to come from 500 years» worth of coal
supplies and lots of nuclear power plants —
by this time possibly breeder or
fusion plants.
Supply of fuel, however, is not a problem: it seems that water
by weight contains roughly 100 to 300 times as much energy as gasoline, for the various
fusion reactions that may be feasible «early in the third millenium», as the authors phrase it.