The economies of the world are driven by energy supplies, and the future of these supplies is in question. Most industrialized economies depend largely on petroleum energy supplies, and geologic studies of petroleum resources suggest that the global production of petroleum will peak around the year 2000. In economies of developing countries, the traditional sector depends largely on biomass resources, and the exploitation of these resources is proceeding in a way that is not sustainable in the long term. Coal is a widely available fossil fuel, but its combustion creates many problems, the most severe of which is probably carbon dioxide emissions and the associated greenhouse effect. Nuclear power does not produce carbon dioxide, but it generates radioactive wastes, involves the risk of serious accidents, and complicates the international management of nuclear weapons.