The cost of energy limited the growth of technology until fossil fuels came into use, around three hundred years ago. Fossil fuels contain so much energy that they provide a remarkable return on investment even when used inefficiently.
The abundant, cheap energy provided by fossil fuels has made it possible for humans to exploit a staggering variety of resources, effectively expanding their resource base.
In particular, the development of mechanized agriculture has allowed relatively few farmers to work vast tracts of land, producing an abundance of food and making possible a wild growth of population.
Around 8,000 BC, world population was something like five million. By the time of Christ, it was 200 to 300 million.
By 1650, it was 500 million, and by 1800 it was one billion.
The population of the world reached two billion by 1930.
By the beginning of the 60's it was three billion; in 1975 it was four billion; and after only eleven years it was five billion. Now it crossed 6 billion.
The demand for energy will not remain at current rates; it can be expected to grow at an ever-quickening pace. Hydropower furnishes about 5.5% of the energy currently consumed. Its potential may be as much as five times greater, but this is not sufficient to take over fossil fuels. Moreover, huge dams would submerge rich agricultural soils.
The production of electricity from nuclear fission has been increasing, but nuclear sources still supply only about 5.2% of the world's total energy needs. Fission reactors could produce a great deal more, especially if fast-breeder reactors were used.
But anyone with a fast-breeder reactor can make nuclear weapons, so there is considerable political pressure to prevent the proliferation of such reactors.
Moreover, public confidence in all types of reactors is low, and the cost of their construction is high. These social constraints make it unlikely that fission's contribution to the world's energy needs would grow fast in the next few years.
Controlled thermonuclear fusion is an alluring solution to the world's energy problems because the "fuel" it would use is deuterium, which can be extracted from plain water.
The energy from one percent of the deuterium in the world's oceans would be about five hundred thousand times as great as all the energy available from fossil fuels. But controlled fusion is still experimental, the technology for its commercialization has not yet been developed, and the first operational facility could not come on line much before 2040.
Visionaries also support the potential of wind, waves, tides, ocean thermal energy conversion, and geothermal sources.
All of these might be able to furnish a portion of the energy in certain localities, but none can supply 75% of the world's energy needs. Solar thermal collection devices are only feasible where it is hot and sunny, and photovoltaic are too inefficient to compete with the cheap energy available from fossil fuels.
While no single energy source is ready to take the place of fossil fuels, their diminishing availability may be offset by a regimen of conservation and a combination of alternative energy sources.
Technology must find a way to fuel itself, and extensive research could find the right combinations of energy sources for a balanced technological growth.