What will energy use patterns in the year 2100 look like? Such long-term predictions are difficult, risky, and perhaps impossible. Could an American citizen in 1860 have predicted what the pattern of today's energy use would be like?

Yet, there are reasons to believe that some dramatic changes in the ways we use energy may be in store over the next century. Most importantly, the world's supplies of nonrenewable energy—especially, coal, oil, and natural gas—continue to decrease. Critics have been warning for a least two decades that time was running out for the fossil fuels and that we could not count on using them as prolifically as we had in the past.

For at least two decades, experts have debated the best way to structure our energy use patterns in the future. The two most common themes have been described...