I have always thought that the answer to the question in the subtitle of this David Owen article was clear: make the things we do with energy using less of it. Now I am rethinkng that proposition. Owen writes about the application of "Jevons paradox" to energy consumption: the economical use of a resource results not in less consumption, but of more! This theory was published in 1865 by William Stanley Jevons in a remarkable book, "The Coal Question", and has been revisited by many modern economists, including William Nordhaus of Yale and others, who often call the effect "rebound". To the extent that it is applicable, it makes the sanguine assertion that we can conserve our way out of the energy crisis somewhat problematic. For example, making refrigeration and air conditioning more efficient has led to more rather than less energy being used for those purposes. The efficiency of residential air conditioners increased by twenty eight percent between 1993 and 2005, but the energy consumed for cooling increased by thirty seven percent during the same period. Economists are arguing about how widely the Jevons paradox is applicable, but the situation is not as straightforward as most of us naively believe.