Coal
Coal is a combustible black or brownish-black sedimentary rock composed mostly of carbon and hydrocarbons. It is a nonrenewable energy source because it takes millions of years to create. The energy in coal comes from the energy stored by plants that lived hundreds of millions of years ago, when the earth was partly covered with swampy forests. For millions of years, water and dirt buried layers of the dead plants at the bottom of the swamps, trapping the energy of the dead plants. The heat and pressure from the top layers helped the plant remains turn into what we today call coal.
Worldwide coal reserves are slightly more than one trillion tons—enough to last approximately 180 years at current consumption levels. The countries with the largest reserves of coal are the United States, Russia, China, and India. Together they make up 67% of the world’s coal reserves.
In 2003, the last year for which world data are available, coal accounted for 24% of world energy consumption. The US Energy Information Administration expects coal use to double by 2030 to meet rising world energy demand.
In some countries, coal may be burned directly for heat or cooking, but most coal is used in power plants to generate electricity. Coal-burning power plants can be sources of air emissions, generating substantial greenhouse gases. But new technologies significantly reduce these emissions.
