Jevons paradox

Jevons paradox is the observation that making a resource more efficient to use can increase, rather than decrease, total consumption of that resource. It is named for the economist William Stanley Jevons, who observed in his 1865 book The Coal Question that improvements in the efficiency of steam engines, far from reducing Britain’s coal consumption, increased it, because cheaper, more efficient engines made steam power economical for many more uses than before.

In software and computing, the paradox is invoked wherever an efficiency gain makes a resource cheap enough to use more liberally, offsetting or reversing the expected saving. Faster processors and cheaper memory, rather than letting programs run within a fixed resource budget, have historically enabled software to grow more resource-hungry, a pattern related to Wirth’s law's observation that software expands to consume the hardware gains meant to speed it up. More efficient caching or compression can similarly lead to systems being used more heavily, saturating other parts of the system that the efficiency gain did not touch.

The paradox is a caution against assuming that an efficiency improvement automatically translates into a proportional resource saving at the system level. Whether it does depends on whether demand for the resource is elastic: whether cheaper access unlocks new uses that were not economical before.

See also

• Laws and principles

References

• Jevons, William Stanley (1865). The Coal Question: An Inquiry Concerning the Progress of the Nation, and the Probable Exhaustion of Our Coal-Mines. Macmillan.