What is the rebound effect in energy efficiency improvements?

• A. Efficiency gains always reduce total energy use.
• B. Efficiency gains lower costs, which may increase or maintain energy consumption, offsetting some savings.
• C. Rebound only occurs with heating systems.
• D. Rebound means energy prices increase after efficiency.

Answer: (B)

The rebound effect shows that making energy use more efficient often lowers the cost of using energy, which can lead to using more energy services or engaging in more activity, so total energy use doesn’t drop as much as expected and can even rise in some cases. When a device or system runs more efficiently, you pay less per unit of service (like heating per hour or miles driven). That lower cost can encourage keeping the indoor temperature a bit warmer, driving more miles, or buying and using more energy-using devices. As a result, total energy consumption may fall, but not by as much as the efficiency gain alone would suggest, and it can offset a portion of the savings.

This idea is illustrated by examples outside heating: a more efficient car costs less to operate per mile, which can lead to more driving; an efficient appliance runs cheaper to operate, which can lead to running it longer or buying more of it. The key point is the link between lower energy cost and increased or maintained energy use, rather than the notion that efficiency automatically and always reduces total energy use.

The other statements don’t fit because rebound isn’t limited to heating systems, and efficiency does not cause energy prices to rise as a direct consequence.