US energy-related CO2 emissions declined in 2019, nearly all due to the electric sector

U.S. energy-related carbon dioxide emissions declined by 3% in 2019 relative to the prior year, almost entirely due to the changing mix of fuels used to generate electricity. Transportation now exceeds electric power as the energy-related sector contributing the most CO2 emissions, according to recently released federal data.

 

The U.S. Energy Information Administration tracks estimated domestic energy-related CO2 emissions, by multiplying energy consumption, measured in British thermal units, by a "carbon factor" representing the average carbon intensity of each source. According to EIA, total energy-related CO2 emissions in 2019 decreased by about 150 million metric tons (MMmt) relative to their 2018 level. This roughly reverses the 3% year-over-year increase experienced in 2018.

Through the twentieth century, the electric power sector was responsible for the largest share of domestic carbon emissions. U.S. total energy-related CO2 emissions peaked in 2007, and have since declined by about 15%.

U.S. total CO2 emissions from the electric power sector also peaked in 2007, but have since declined even more than than other energy-related sectors. According to EIA data, U.S. electric power sector emissions have fallen 33% below their 2007 peak "because less electricity has been generated from coal and more electricity has been generated from natural gas (which emits less CO2 when combusted) and non-carbon sources." 

This trend toward decarbonization of the electric power sector continued in 2019, leading EIA to attribute nearly all (96%) of the 2019 year-over-year decline to changes in the fuels and resources used to generate electricity. In particular, non-carbon-emitting generation such as nuclear and renewable sources generated a record 38% of total U.S. electric generation in 2019.  As a result of these changes and energy efficiency gains, EIA calculates the total carbon intensity of domestic electricity has fallen from 619 metric tons per megawatthour (mt/MWh) in 2005 to 408 mt/MWh in 2019.

Transportation has long been a significant contributor of CO2 emissions. While U.S. transportation-related CO2 emissions declined slightly in 2019, the transportation sector now emits more CO2 than any other energy-related sector tracked in EIA's carbon reporting. In some states, such as Maine, the transportation sector is responsible for more than half of all tracked carbon emissions.