Short answers, pulled from the story.
The rebound effect is the reduction in expected gains from technologies that increase resource efficiency, caused by behavioral or systemic responses that increase consumption. It is measured as the ratio of lost benefit compared to the expected environmental benefit when consumption is held constant. A 5% improvement in vehicle fuel efficiency that produces only a 2% drop in fuel use represents a 60% rebound effect.
William Stanley Jevons first described the rebound effect in his 1865 book The Coal Question. He observed that a more efficient steam engine made coal economically viable for many new uses in Britain, ultimately increasing total coal demand even as the coal required for any single use fell. The phenomenon became known as the Jevons paradox.
The Khazzoom-Brookes postulate is the idea, named by economist Harry Saunders in 1992, that energy efficiency gains paradoxically result in increases in energy use. Saunders modeled it across a range of neoclassical growth models and found the postulate held under a wide set of assumptions. It builds on earlier work by Daniel Khazzoom and Len Brookes on the relationship between efficiency and energy consumption.
In developed countries, the direct rebound effect for residential space heating and cooling typically ranges from roughly 5% to 40%. Studies of direct rebound effects across energy services broadly find a figure of around 30%. Low-income households tend to show higher rebounds than high-income households because they are more price sensitive.
Households given solar-powered lighting saw daily lighting hours rise from an average of two to six, because the solar lamps carried essentially zero operating cost. Direct rebounds ran between 50 and 80%, and the combined direct and indirect rebound exceeded 100%. Households continued using kerosene lamps alongside the solar lamps, and increased lighting enabled more cooking and expanded food trade with neighboring villages.
Mathis Wackernagel and William Rees proposed taxing away cost savings from efficiency gains and directing them toward natural capital rehabilitation. Specific instruments include green taxes, cap and trade programs, higher fuel taxes, and a restore approach that redirects part of the savings back to the resource. Vivanco, Kemp, and van der Voet outlined three broader strategies: raising environmental efficiency economy-wide, shifting consumption toward greener goods, and reducing absolute consumption.