Natural gas can provide twice the energy that coal does per unit weight, and natural gas produces around half of the carbon dioxide produced by coal per unit of power (Cathles et al., 2012, p. 531; Clark, 2013). Coal combustion emits 93 tons of carbon dioxide equivalents per terajoule of electricity, while natural gas produces 57 tons of carbon dioxide equivalents per terajoule (Broderick et al., 2011, p. 109). A terajoule is the same amount of solar energy that reaches an area of 1.5 football fields in one day. Natural gas is also considered to be a cleaner fuel than coal because it does not produce sulfur, mercury, ash, and particulates that are harmful to the environment and human health (Cathles et al., 2012, p. 526). Hayhoe et al. (2002) shows that substituting gas for coal using a 100-year span instead of a 20-year span does reduce global warming potential. “They consider the warming effects of decreasing [sulfur dioxide] and black carbon emissions as coal burning is reduced, as well as the warming effects of [carbon dioxide] and [methane] emissions” (as cited in Cathles et al., 2012, p. 527).
When the full life-cycle greenhouse gas emissions are analyzed, including the production and combustion emissions, the advantage of natural gas is maintained only when burned in modern and efficient power plants. A coal-fired power plant has a thermal efficiency on average of 33 percent, while a gas-fired plant ranges in efficiency from 40 to 60 percent (IEA, 2012, p. 6; as cited in Broderick et al., 2011, p. 63). Before the EPA revised its emissions estimate, the average gas-fired power plant was about 32 percent cleaner than coal-fired power plants, according to Paulina Jaramillo, an assistant professor of engineering and public policy at Carnegie Mellon University. However, about half of the 1,600 U.S. gas-fired power plants “operate at the lowest end of the efficiency spectrum.” Currently, the median U.S. gas-powered plant is just 40 percent cleaner than coal, while the 800 inefficient gas-fired plants offer only a 25 percent advantage, according to calculations by ProPublica based on Jaramillo’s formulas.
As the advantages of natural gas versus coal become smaller with revised emissions estimates, the political push for a move to natural gas becomes weaker. Power utilities are apprehensive to invest in a fuel that may lose the government’s support in the long run. “Billions of dollars of taxpayer and industry investment in new infrastructure, drilling and planning could be spent for limited gain” (Lustgarten, 2011b).