Energy sources: a realistic outlook.

Projections to the middle of the next century indicate that unabated historical global energy trends would lead to an annual global energy demand about four times present levels, primarily due to population and economic growth. But extensive global conservation and energy-efficient systems might reduce this value by half. The cumulative effect of the coming half century's use may strain the world's low-cost resources, particularly oil. The future fuel mix is further complicated by the environmental thrust to reduce the global use of carbon-based fuels. The interaction of the principal factors influencing future energy resource and technology options are projected.