Coal is formed from plant matter that was buried and is unable to biodegrade naturally, usually in low lying wetlands, resulting in a lack of oxygen needed for aerobic bacteria to digest it. It is initially turned into peat which then, as it is more deeply buried, slowly turned into lignite, then bituminous coal and finally anthracite coal. Coal is used in several ways such as being burned as fuel, or it can be converted into useful materials, such as mineral coke which is commonly used in steel refining, or as a precursor in producing chemical fertilisers such as ammonium nitrate. As a fuel source it is believed to have been used for at least 6000 years - being used for heating as well as the smelting of metals.
Coal is the most widely used means of energy production with the U.S. Energy Information Agency estimating 7.5 metric gigatonnes (8.3 x 109 short tons) being consumed in 2011 producing 8.584 TWh of electricity, an estimated 40 % of the world’s total power (Derived from World bank – world development indicators). New Zealand is less reliant on coal than most countries with 61.6 petajoules (pJ) of power being produced from coal out of 904.8 pJ total (6.8%) thanks to abundant renewables that provide about 40% of our energy . This is set to end in 2016 with the last remaining large scale coal fired power plant, located in Huntly, set to close. New Zealand does still have an estimated 15 billion tonnes in known reserves and exporting nearly 4 million tonnes annually, or 44% of domestic production.
While being one of the most abundant fuels it is also one of the dirtiest from its mining to its consumption. Its affects have been well documented from the great smog of 1952 in London that killed an estimated 4000 people, and more recent incidents of smog in the likes of Delhi and Beijing, to black lung disease in miners as a result of inhaling coal dust, and environmental pollution such as the water contamination resulting from the Kingston fossil plant spill in Tennessee in 2008. It also releases nitrous oxides, SO2, that causes acid rain, and is the largest source of CO2 - the main cause of global warming, as well as being responsible for the emission of mercury that contaminates food and water sources. Attempts to develop cleaner alternatives have yielded results, such as carbon capture and sequestration, however these technologies fail to fully deal with the issue and leave near permanent sources of pollution that could leak.
The Pike River Coalmine disaster in 2010, in which 29 men lost their lives, is the worst mining disaster in the last 100 years. It occurred due to a spontaneous explosion of methane built up in the mining tunnels.