This obscure Civil War-era figure gave us a paradoxical warning. Do we have time to heed it today?

In 1865, the economist William Stanley Jevons looked at the industrializing world and noted a distinct, counterintuitive rhythm to the smoke rising over England. The assumption of the time, a naive view that persists with a certain obstinacy, was that improving the efficiency of coal use would lead to a conservation of coal. Jevons observed precisely the opposite. As the steam engines became more efficient, coal became cheaper to use, and the demand for coal did not decline; it skyrocketed.

This phenomenon, later called the Jevons Effect, suggests a fundamental truth of economics that we seem determined to forget: When a resource becomes easier and cheaper to consume, and demand for it is elastic, we do not consume less of it. We often consume a great