Environmentalists argue that energy efficiency mandates will save the climate by cutting energy consumption and thereby reducing greenhosue gas emissions. But consumers often take what they "save" through energy effiiciency in one place and "spend" it on more energy intensive products and services elsewhere. Big improvements in efficiency fueled consumers desires for bigger faster cars not better gas mileage. The demand for energy for lighting has exactly offset many-thousand-fold efficiency gains in lighting technologies over the past three centuries. It's a lot cheaper per square foot to heat and cool a house, so consumers build bigger houses. Reason Science Correspondent Ronald Bailey looks at how energy rebound undermines centrally planned energy efficiency.