"Since May 2012, a combination of higher prices for natural gas and increased demand for electricity during the summer months led electric systems across much of the country to increase their use of coal-fired units. In March 2013, coal-fired units generated a little over 130,000 megawatthours of electricity, while natural gas units produced nearly 85,000 megawatthours. Heading into the 2013 spring shoulder season (between winter and summer), when demand for electricity typically falls, higher prices for natural gas reduced the fuel's share of total generation below the record levels of last April."
While coal's power generation cost has dipped slightly from $2.41 per million Btu (British thermal unit) in March 2012 to $2.35 per million in March 2013, natural gas has risen from $2.96 per million Btu to $4.30 per million in the same period, a separate EIA report shows. The agency forecasts that gas will rise to $4.74 next year while coal will nudge up to $2.44.
Both fossil fuels emit nitrogen oxide pollutants and CO2 - a greenhouse gas that heats the planet - but coal's emissions are significantly higher. Natural gas' nitrogen oxide is about 30 percent of coal's, and its CO2 about 43 percent or slightly more.