emissions in the atmosphere at the same time as it is planning to triple, even quadruple, its energy use. By 2100, the world that these children's children will inhabit may need 30 or 40 trillion watts. And to prevent massive greenhouse build-up, most of this must be carbon-free. MARTY HOFFERT: The magnitude of the job is massive. If you confront the problem honestly - I mean, if you really look at the problem, and you say, "What I want to do is I want to stabilize the amount of carbon dioxide in the atmosphere at some level twice the pre-industrial level of CO2 - it's almost impossible to do that unless there is a truly massive transition in the global energy system away from fossil fuels. That is the bitter pill at the bottom of all of these discussions. NARRATOR: If America consumes ever larger amounts of energy, and if the developing nations follow in its footsteps, then the world must sooner or later confront an awesome challenge: to find a carbon-free replacement for fossil fuels. Where will this energy come from? Some say the technology has already been invented- renewable energy. Solar power, the energy of the wind, and biomass, the growing of vegetable matter to use for fuel. DAN LASHOF, Natural Resources Defense Council: I think it is very credible that over a longer period of time, we can get the majority of our electricity from new renewable energy sources. NARRATOR: Others argue that what we need is