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Low rank coal tends to have a smoky flame and easy ignition whereas high rank coal is known for its clean flame and difficult ignition.  All of these types of coals can be found in three major United States regions known as The Appalachian Basin, The Illinois Basin, and the northern Great Plains and Rocky Mountain region.  To recover coal from these significantly large coal reserves, workers use a process called strip mining. By using this process, strip miners can recover all the coal in a deposit, and each worker achieves very high productivity, recovering 30-40 tons per worker per day. Sixty percent of coal in the United States comes from strip mining.
Burning of fossil fuels contribute to a highly carbon dioxide emissions, which causes global warming. Coal has been using as the largest and primary resource of fossil fuel for generating the electricity, heat, and industrial purposes. Due to the high content of carbon dioxide in coal, it produces a high percentage of carbon dioxide emission into the atmosphere more than other fossil fuels, when it is combusted (Biologicaldiversity.org, 2014). By 2012, 41 percent of global electricity is generated by coal-fired power plants and it accounts for 39 percent of U.S electricity, which is equal around 83 percent of greenhouse gas emissions in the United States (Worldcoal.org, 2014). Furthermore, the second largest source of carbon dioxide producer is petroleum, which emits about three-fourths of carbon dioxide as combustion of coal (Biologicaldiversity.org, 2014).