Fossil fuels continue to be the main source of energy consumption in the United States, which uses a quarter of the world's oil and a fifth of all the coal consumed each year. Globally, total energy use is projected to increase more than 50 percent by 2025, with the fastest growth expected in emerging economies such as China and India. Although energy is central to the modern human existence, the effects of producing and using fossil fuels have grown increasingly severe -- depleting a nonrenewable source of energy while creating pollution and greenhouse gases. Environmentalists, politicians and industry leaders are calling for the development of newer, more efficient energy technology and the reduction of our dependence on fossil fuels. What is the future of energy?