Stanley Jevons was a 19th century polymath who became fascinated with the idea of analyzing everyday problems through mathematics. He invented the concept of “marginal utility,” now an essential of economics, and in 1870 demonstrated to the Royal Society a “Logic Piano,” which was an early version of the computer. Jevons greatest contribution, however, is probably the “Paradox” he observed in studying the history of coal consumption.
Jevons calculated that James Watt’s redesign of the steam engine had improved its efficiency by a factor of ten over the original 18th century design of Thomas Newcomen. Therefore, you might expect that coal consumption in Britain would have declined. Instead, it had increased by a factor of ten. Why? Jevons realized that when energy efficiency improves, people are more likely to demand more consumption using the same amount of energy rather than producing the same amount of goods using less energy. Thus, as steam engines became more efficient, wider and wider applications were found and coal consumption multiplied. This paradox is discussed at much greater length in a recently published book, The Conundrum, by New Yorker writer David Owen.
You can see Jevons’ Paradox in action by comparing the above graph with the previous one of energy used per dollar of GDP. Although we use less energy per dollar, energy consumption has still risen steadily from 75 quadrillion BTUs (“quads”) in 1974 to just under 100 today. This is both because GDP growth has outstripped the efficiency improvements and because of Jevons' Paradox - people elect to employ these improvements to increase consumption rather than to decrease energy input. The only time energy consumption has decline absolutely has been during periods of recession from 1974-75, 1979-1982 and 2008-2010.
The lesson is this: Those who believe we can decrease our overall energy consumption through improvements in efficiency are likely to be disappointed.