COPENHAGEN–Revolutionizing the energy industry to achieve a target concentration of greenhouse gases in the atmosphere of no more than 450 parts per million (ppm) would require building 17 nuclear power plants a year between now and 2030; 17,000 wind turbines a year; or two hydropower dams on the scale of Three Gorges Dam in China, according to the International Energy Agency . Such an effort would require an investment of $10.5 trillion during the next 20 years but would ultimately yield savings of $8.6 trillion, the IEA estimated. [More]