It launched the Industrial Revolution, birthed the modern energy economy, and put civilization on a trajectory toward hypercomplexity and exponential growth. And now that remarkable rock that burns is helping cook the planet.

Coal is the fossilized remains of ancient plants that accumulated on the bottom of shallow water bodies before being buried by sediment during the Carboniferous and Permian periods some 363–245 million years ago. There are four basic kinds of coal, which vary in their energy density due mainly to carbon content: Anthracite has the highest energy content, followed by bituminous, sub-bituminous, and lastly lignite (also called “brown coal”).

Large coal deposits are located in the United States, Russia, China, and Australia. Globally, coal use is increasing rapidly, particularly in China, which burns roughly half of the world’s annual coal production. Consequently, China has become the world’s leading emitter of greenhouse gas pollution. The United States, sometimes called the “Saudi Arabia of coal,” has roughly 29 percent of the world’s coal reserves,which are used to provide nearly half of U.S. electricity generation. There are more than 600 coal-fired electricity generating facilities in the United States, with dozens of new ones either under construction or seeking permits. Clean energy activists have successfully blocked more than a hundred proposed coal plants in recent years, and low natural gas prices are leading utilities to close some older, heavily polluting coal plants or convert them to natural gas.

Coal is relatively easy to mine, transport, and store and is perceived to be a cheap source of energy. It is very expensive, however, if the associated ecological and public health costs are considered. A 2011 study published in the Annals of the New York Academy of Sciences attempted a full life-cycle accounting of coal’s public health and environmental costs; it estimated that these “externalities” may exceed $500 billion annually in the United States alone. Coal combustion can also release large quantities of toxins including mercury, lead, arsenic, and sulfur dioxide. Particulates released by coal burning are also a major pollutant and are blamed for tens of thousands of heart attacks and premature deaths in the United States each year.

Globally, coal burning is responsible for more than 40 percent of human-caused carbon dioxide emissions, and thus is a key factor in climate change. Coal mining, processing, and burning also produce vast amounts of liquid and solid pollution including coal combustion ash, which has caused contamination in dozens of states according to EPA and conservation group studies.

Recent efforts have sought to clean up coal’s image with promises of carbon capture and storage (CCS) and smokestack scrubbers. But there are serious doubts about the scalability of CCS technology, and both sequestration and scrubbers require additional energy—meaning yet more coal must be burned to generate the equivalent energy delivered to consumers.