"Technological change will not necessarily reduce dependence on fossil fuels. Energy taxes or a system of caps on energy use and trade in emissions permits are necessary," Eckaus said in a statement. "There is no a priori reason to think technology has the potential for reducing energy use while meeting the tests of economics. It's politically unappetizing in the U.S., but in Europe, gas costs $6 a gallon. Make energy more expensive: People will use less of it."