Our modern society requires power and that is not going to change. The cost of power is a key factor in determining the cost of production, and the cost of living. Although power plants are regulated by federal and state laws to protect human health and the environment, there is a wide variation of environmental impacts associated with power generation technologies. In the U.S. natural gas is used to produce 21 % of its electricity. Coal is used to product 48 % of electricity. With the existing power plants in place coal is still much cheaper than natural gas for generating electricity, but the tightening of regulations by the EPA under the Clean Air Act of coal powered generating plants for carbon emissions, mercury, arsenic, acid gases and the Cross-State Air Pollution Rule (even with recent modifications) will decrease that financial advantage because coal burns dirtier than natural gas.
The nation's coal-fired power plants were built as the nation grew and industrialized in the first half of the 20th century when coal was the most abundant and cheapest available fuel. The coal burning power plants emit 48 tons of mercury annually as well as particulates and other pollutants. According to the EPA, Mercury can cause neurological disorders in children and the mercury emissions from power plants pose "significant hazards to public health" and must be reduced. By forcing the plants to curb emissions of mercury, arsenic and acid gases, the EPA says it can prevent as many as 17,000 premature deaths a year caused by breathing air laced with coal-fueled pollution. These new regulations will require existing plants to meet emission standards that are at least as stringent as the top 12% best-performing coal facilities and may force some plants to convert to natural gas fuel or to shut down entirely. The generating capacity will have to be replaced with new plants that burn cleaner fuels and produce less pollution, but the cost of power will increase.
The mercury, arsenic, and acid gas regulations should not be confused with the Cross-State Air Pollution Rule which is a separate set of EPA regulations, aimed at slashing smokestack emissions that can travel into neighboring states, and were recently changed to allow 10 states (notably Texas who sued the EPA), to emit more smog-causing pollution than had initially been permitted. The change will allow the 10 states to emit 76,000 tons more pollution (70,000 tons will come from Texas) or about 2% of the total pollution the EPA will regulate under this new rule. The rule is designed to decrease smokestack emissions, mostly from coal-fired power plants, in 27 states, that contribute to unhealthy air downwind and is expected to prevent up to 34,000 untimely deaths and combined with the other rules will prevent 51,000 premature deaths, but the cost in terms of increased electrical rates, jobs and lives disrupted by unemployment and diminished economic opportunity. The recent changes give more leeway to the dirtiest facilities, but the EPA explains that the change was made because it became apparent that air stack scrubbers were not as efficient as initially assumed in the EPA’s first version of the Cross-State Air Pollution Rule. Nonetheless, the primary impact of the new rules will be on coal-fired plants more than 40 years old that have not yet installed state-of-the-art pollution controls. Many of these plants are inefficient and will be replaced by more efficient combined cycle natural gas plants. Edison Electric Institute, an industry trade group, claims the combined new rules will cost utilities up to $129 billion and eliminate one-fifth of America's coal capacity.
Natural gas is the cleanest of the fossil fuels. Burning natural gas in the place of coal emits fewer harmful pollutants. Methane, the principle component of natural gas, is itself a potent greenhouse gas. Methane has an ability to trap heat almost 21 times more effectively than carbon dioxide. This year researchers at Carnegie Mellon University compared greenhouse gas emissions from the Marcellus Shale region with emissions from coal used for electricity generation. The authors found that natural gas from the Marcellus shale had lower life cycle greenhouse gas emissions than coal for production of electricity by 20–50% depending upon plant efficiencies and natural gas emissions variability. Shale sourced natural gas could provide a reliable source of natural gas for our nation in this century and might make the conversion of some power generation worthwhile. However we need to remember that the gas still is a limited resource and be cautious about what other impacts fracking might have on our other resources especially water. At least in the medium term the environmental impact from power generation will be determined by the efficiency and care of how fuel is obtained, transported, generated and used. Improving efficiency is the low lying fruit that can have an immense impact and should not be ignored while we are busy dreaming of the someday world of renewable energy. Natural gas from shale rock is plentiful in North America. Despite billions of dollars in DOE solar generation loan guarantees the generating capacity of solar power in the nation will continue to be under 3% of power generation.