Oil, gas, and coal now provide most of the world's energy. But burning these fossil fuels releases carbon dioxide gas (CO2). By holding in the heat like a blanket, CO2 changes the flow of heat in the atmosphere and can ultimately change the earth's climate. Many scientsts believe that if the rate of burning fossil fuels continues to rise, those climatic changes could disrupt agriculture and trigger famines within our lifetime. Within a century, the sea level could rise enough for rowboats to dock at the steps of the U.S. Capitol. The climatologists assumed massive and increasing use of fossil fuel because most energy planners said it was necessary. The choice, they claimed, was between unpredictable climate shifts, the costs and risks of nuclear power, or energy scarcity and continuing Third World poverty. But the four internationally-known authors of Least-Cost Energy: Solving the CO2 Problem, examining this conventional wisdom afresh, find it badly out of date. It is simply not true that prosperity and global equity require ever-increasing use of fossil (or nuclear) fuels. Newly developed technologies can provide the same energy services more cheaply by wringing more work out of our energy and by harnessing the renewable energy flows of sun, wind, water, and biomass wastes. This "least-cost energy strategy" - one that seeks to meet society's needs at the lowest possible economic cost, as would occur in a competitive free market - would make it unnecessary and indeed uneconomic to burn the fossil fuels that threaten the world's climate.