Page - 62 - in Water, Energy, and Environment - A Primer

temperaturesandpressuredeepintheEarthovermillionsofyears, was firstmentioned in the 16th century. Today, it is understood that petroleum and natural gas are the products of anaerobic (low oxygen) decomposition of dead organisms such as aquatic phytoplankton and zooplankton. Coal and natural gas are understood to be decomposition products of terrestrial plants. While these processes are still underway, fossil fuels are considered to be non-renewable resources because they take tens to hundreds of millions of years to form, while they are being consumedat high rates today. 6.1 COAL Coal isusedprimarily toheatwater toproduce steamtogenerate electricity. China is the world’s leading coal producer (45%), followed by the US at 11%. Just over one third of global electricity is currently generated by burning coal. While the world has large reserves of coal, its downside is that coal combustion produces a wide range of air pollutants that are harmful to human health and the environment. These include sulphur dioxide (SO2) which is responsible for acid rain; nitrogen oxides (NOx), a family of oxides that contribute to the formation of smog, acid rain, and ozone; mercury (Hg), a cumulative poison when taken into the body; and radioactivity from elements like uranium and thorium that are often found in coal deposits. As discussed in Chapter 4, coal combustion is also amajor source of the greenhousegasCO2. The term ‘cleancoal’was introduced in2008bycoal industry groups at a time when the US Congress was considering legislation to limit CO2 emissions.While deliberately vague, it is usually interpreted to mean coal-fired power plants that capture and sequester the CO2 emitted from smokestacks. This process has been given the name Carbon Capture and Sequestration (CCS). It is a complex and contentious approach to reducing CO2 emissions from industries such as power Water,Energy, andEnvironment–APrimer62