From 1950 to 1985, U.S. electric power sector CO2 emissions increased from just 278 million metric tons to 1.6 billion metric tons. By this point, emissions from electric power had overtaken those produced by both the industrial and transportation sectors to become the most polluting U.S. sector. Power sector emissions continued to rise in the following years as electricity demand grew, and by 2007 electric power-related emissions had reached a peak of 2.42 billion metric tons of CO2. Since then, however, electricity-related CO2 emissions have been on a downward trajectory, and by 2016 they had fallen back below transportation sector emissions, and in 2020 they dropped to 1.45 billion metric tons.
Sources of U.S. power emissions
Coal combustion is the main source of electric power sector emissions. Coal is the most carbon-intensive electricity source and produces roughly twice as much CO2 when burned as natural gas. In 2007, coal power emissions totaled 1.9 billion metric tons - roughly 80 percent of total U.S. power sector emissions that year. Although coal-fired emissions had dropped to 786 million metric tons in 2020, they still accounted for more than 50 percent of electricity-related emissions. Some of the biggest polluters in the United States are coal-fired power plants, such as the James H. Miller Jr plant in Alabama. From 2009 to 2019, five of the most polluting power plants in the U.S. had emitted more than one billion metric tons of CO2, with the James H. Miller plant producing more than 240 million metric tons alone.Many of the most polluting power plants are in Texas, whose electric power industry produced 218 million metric tons of CO2 emissions in 2020. Although this was far higher than emissions from electricity generation in any other state, electric power emissions in Texas have fallen by more than 17 percent since 2005.
Why have electric power emissions fallen in the U.S.?
In addition to the rapid growth of renewable energy, there are several other factors as to why electric power sector emissions have fallen so substantially in the U.S. Technological advancements have vastly improved energy efficiency, while environmental policies - such as the Cross-State Air Pollution Rule (CSAPR) – have led to the closures of many coal-fired power plants across the country. Low natural gas prices fueled by the fracking boom have also resulted in coal-fired power plants switching to natural gas. In 2007 - when power sector emissions peaked – coal accounted for half of the U.S. electricity mix. By 2020, coal’s share of electricity generation had fallen to less than 20 percent. In comparison, natural gas and renewables shares had increased to 41 percent and 20 percent, respectively. The transition away from coal power has also helped lower sulfur dioxide emissions from electric utilities, which in turn has also lowered the number of deaths attributable to air pollution.The U.S. power sector has made substantial progress in reducing its emissions over the past 15 years. In 2005, “business as usual” projections by the EIA showed that electricity demand would have increased between 2005 and 2020, with coal power generation remaining the primary source of electricity. This would have seen power sector CO2 emissions increase to more than three billion metric tons by 2020. Actual 2020 emissions were roughly 50 percent lower than these projections. Thus, the U.S. is now halfway towards a carbon-free power sector, and there have been proposals to decarbonize the power sector by 2035. Currently, 17 states have set targets of reaching 100 percent clean electricity by 2050 or sooner.
