Emissions of sulfur dioxide (SO₂), nitrogen oxides (NOx) and carbon dioxide (CO₂) from the electric power sector will remain mostly flat through mid-century, assuming no changes to current laws and regulations.

The Energy Department's Energy Information Administration (EIA) said that SO₂ and NOx emissions have declined over the past several decades, largely because of regulations put into effect under the Clean Air Act Amendments of 1990.

For SO₂, the regulations included acid rain cap-and-trade program deadlines in 1995 and 2000. One of the main regulations affecting NOx emissions was the 2003 expansion of the Environmental Protection Agency’s (EPA) NOx Budget Trading Program (Title I) to include most states east of the Mississippi River.

In addition, the EPA’s Mercury and Air Toxics Standards (MATS), announced in 2011 and implemented in 2015, required power generators to comply with emissions limits for toxic air pollutants associated with fuel combustion such as mercury, arsenic and heavy metals. Although MATS targets mercury and air toxics emissions, power plants’ compliance with the rule also decreased emissions of SO₂ and NOx.

None of these programs targeted CO₂ emissions explicitly, but EIA said they did indirectly affect the economics of power plant fuel use and operation rates as well as plant investment and retirement decisions. CO₂ emissions in the U.S. electric power sector have been generally declining since their 2007 peak of 2.4 billion metric tons (mt).

EIA projects that electric power sector CO₂ emissions will remain relatively unchanged through mid-century, falling by around 0.1 billion metric tons from 2018 through 2050. By 2050, U.S. electric power sector emissions will be about 1.6 billion metric tons, or nearly equal what they were in 1984.

Although emissions are expected to remain relatively flat, EIA projects a 23% increase in electricity generation from 2018 to 2050. Added electricity generation is expected to come mostly from natural gas and renewable energy resources, which emit less or no carbon dioxide as part of their electricity generation.

EIA said that more than one-third of the coal-fired capacity in place in 2018 is expected to retire by 2050, largely because of decreased competitiveness with relatively low cost natural gas combined-cycle generators that operate at high efficiencies. Also, renewables that are currently benefiting from production and investment tax credits and state renewable portfolio standards have seen cost reductions in recent years that make them more competitive in the future.

The largest source of new generation capacity in the projection is from renewable energy, principally solar photovoltaic, and in the near term, wind. Combined renewables generation capacity across all sectors will increase by almost 400 gigawatts (GW) by 2050, EIA said. The next largest source of added generation capacity will be from natural gas, about 360 GW.

These additions of low- and non-carbon generation capacity will allow generation to increase while holding CO₂ emissions mostly flat. The carbon intensity of the electric power sector, expressed in tons of CO₂ per megawatt hour produced, is projected to decline by 26% from 2018 to 2050, or slightly less than 1% per year.