It's all comes from deep inside the earths.

Coal is the most important fuel producing electricity in around the world, but it is also the most controversial. As the greatest source of carbon dioxide of all fuels, environmentalists say it is critical to reduce the world's dependence on it in order to stem global warming.

Coal is a fossil fuel, and a sedimentary rock that is formed by geological action over millions of years. It has been used for various purposes since at least the Bronze Age more than 4,000 years ago. Today it is primarily used as a fuel source for power; power plants burn coal to make steam, which then turn turbines. It is also used for coking for metallurgical applications. The high temperatures created by the use of baked coal, known as coke, give steel its strength and flexibility. The paper and concrete industries also use coal in manufacturing.

While coal is contentious, coal consumption is growing. According to a recent U.S. Energy Department study, world coal consumption could increase by 65 percent between 2005 and 2030. Its share of world energy consumption could increase over that period from 27 percent to 29 percent.

As the economies of Asia, particularly China, rebounded from the 2008 global slowdown, their imports of coal soared, pushing prices up. By 2010, China was using half of the six billion tons of coal burned each year, and the price had doubled over five years.

Coal's preponderance is a reason why the U.S. government invests and encourages private efforts in carbon capture and sequestration efforts to lesson coal's impact on climate change, although most experts think a breakthrough is several years away at best.

In a few places, particularly South Africa, gasification of coal produces synthetic fuels. The Fischer-Tropsch synthetic fuel process was first used on a large scale by Nazi Germany to produce fuels for war.

Coal is mined, often by stripping the tops off mountains that can cause water contamination. The coal industry says that it has improved its practices to protect the environment, and that restoring land disturbed by strip mining in a vital part of the mining process. But coal, which is mined throughout Appalachia, particularly West Virginia and Kentucky, and Montana and Wyoming, is public enemy number one of the environmental movement.

The Energy Department reports that substantial new coal-fired capacity will come on line after 2015 in the United States, even though natural gas is currently the preferred choice for new generating capacity. But China and India should account for nearly 80 percent of the projected increase in world coal production over the next two decades. One reason for all the expected growth is the abundance of coal reserves around the world, including the United States, which is sometimes called the Saudi Arabia of coal.

There are currently about 600 coal-fired power plants across the United States.But while coal has long been considered a reliable and inexpensive source of energy in the United States, it is facing an uncertain future due to growing political pressure on American politicians to impose new regulations controlling its growth. While state and local governments have been blocking new coal plants across the country the last few years, coal executives are preparing for eventual carbon taxes or a cap-and-trade system like on already in place in Europe.

In 2009, Democrats in the House passed such a cap and trade bill, but one with enough concessions and exemptions to win the support of coal-state representatives and dismay environmentalists. A cap and trade bill died in the Senate in early 2010. Legislation developed by Democrats working with Senator Lindsey Graham, a South Carolina Republican, would phase in carbon limits and put more money into carbon sequestration, one of the great hopes for a cleaner coal industry.

In May 2010, the Environmental Protection Agency issued a long-awaited proposal to regulate coal ash, the toxic byproduct of burning coal to produce power. But the agency deferred a decision on whether to treat it as hazardous waste, drawing criticism from environmentalists who had hoped for a stronger stance.

Instead, the agency offered two alternatives, one that would regulate coal ash under strict hazardous-waste rules, and a weaker and less expensive option that would regulate it under the same framework that governs household garbage. The agency will choose between the options sometime after a 90-day comment period.

Either proposal would represent the first time that coal ash, which contains arsenic, mercury and other toxic substances, has been federally regulated. The risk posed by coal ash was made clear in late 2008, when a coal ash pond at the Tennessee Valley Authority's Kingston Fossil Plant in eastern Tennessee ruptured, spilling 5.4 million cubic yards of ash across 300 acres, prompting the E.P.A. to renew a decades-old promise to issue coal ash regulations. The cleanup will cost an estimated $1.2 billion.