Coal

Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements; chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed if dead plant matter decays into peat and over millions of years the heat and pressure of deep burial converts the peat into coal. Vast deposits of coal originate in former wetlands—called coal forests—that covered much of the Earth's tropical land areas during the late Carboniferous (Pennsylvanian) and Permian times. As a fossil fuel burned for heat, coal supplies about a quarter of the world's primary energy and two-fifths of its electricity. Some iron and steel making and other industrial processes burn coal.

The extraction and use of coal cause many premature deaths and much illness. Coal damages the environment, including by climate change as it is the largest anthropogenic source of carbon dioxide, 14 Gt in 2016, which is 40% of the total fossil fuel emissions. As part of the worldwide energy transition many countries have stopped using or use less coal, and the UN Secretary General has asked governments to stop building new coal plants by 2020.

The largest consumer and importer of coal is China. China mines almost half the world's coal, followed by India with about a tenth. Australia accounts for about a third of world coal exports followed by Indonesia and Russia.