The widespread availability of fossil fuels during the 20th century has permitted an unprecedented growth in energy availability - from the meager supplies obtainable from food and wood to today's vastly larger energy supply of coal, oil, and natural gas.

The success of fossil fuels in the marketplace has occurred largely because of their ability to address the most vexing attributes of renewable energy, which is diffuse, intermittent and found in forms (such as photons) that are difficult to use in modern machines. Nature's work over millennia to compress and chemically transform prehistoric organic debris has produced fossil fuels that are rich in energy, easy to store and transport, and readily useable on a large scale.

Electrification of our energy economy and the rise of automotive transportation are two of the most significant technological revolutions of the 20th century, exemplifying the massive change in lifestyle due to the growth in fossil energy supplies. From negligible energy markets in 1900, electrical generation now accounts for 34% of primary energy consumption in the United States, while transportation consumes 27% of our energy supply.² Increased fossil fuel use has financed both energy expansions: coal and natural gas provide more than 65% of the energy used to generate this nation's electricity, while oil fuels virtually all the 190 million vehicles now cruising U.S. roadways. Renewable energy, however, provides less than 2% of the energy used in either market.³

The electricity and transportation energy revolutions of this century have, to date, affected different and largely non-overlapping markets. Electricity is used extensively in the commercial, industrial, and residential sectors, but it supplies barely a blip of energy to transportation markets. On the other hand, oil is not a heavy hitter in electrical generation, now contributing a mere 3% of energy input for electricity.⁴ Oil use in transportation, however, is huge and growing. More than two-thirds of the oil consumption in the United States is used in transportation, mostly to power cars, trucks, and buses. Aircraft account for about 14% of transportation oil consumption, while locomotives and ships are the chief consumers of the remaining 5%.⁵ Annual oil use in the transportation sector alone has surpassed total domestic oil production every year since 1986.⁶

Continued reliance on fossil fuels either for electrification or transportation cannot continue into the indefinite future. The world is currently using fossil fuels 100,000 times faster than they are being recreated by natural forces.⁷ As readily exploitable reserves are consumed, the remaining fossil resources become more costly and difficult to extract. Using the remainder will have troubling political and social repercussions and disturbing environmental consequences, such as global climate change, that threaten the existence of life on Earth.

Completing the energy transformation that began a century ago requires shifting from fossil fuels to sustainable energy systems. This transformation demands the development of energy systems capable of manufacturing energy carriers directly from renewable energy resources, avoiding the detour through fossil fuels.⁸ It took nature eons to create fossil fuels, whereas in just a few years, renewable resources must be captured, concentrated, and stored in energy carriers in sufficient quantities to supply energy end use markets effectively.

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