All people require the production and use of energy. Energy is used for transformation, heating, cooling, cooking, lighting, and industrial production. The world energy supply depends on many different resources including traditional fuels such as firewood and animal waste which are significant energy sources in many developing countries. Fossil fuels – coal, oil and gas – account for more than 90% of global energy production but they are nonrenewable, that is, they can be used up – and their use causes air pollution. In particular, factories using coal have been one of the worst industrial polluters since the beginning of the Industrial Revolution of the 19th century. Moreover, mining or drilling for fossil fuels has caused extensive environmental damage.