Energy and the environment explained Where greenhouse gases come from

In the United States, most (about 74%) human-caused (anthropogenic) greenhouse gas (GHG) emissions come from burning fossil fuels—coal, natural gas, and petroleum—for energy use. Economic growth (with short-term fluctuations in growth rate) and weather patterns that affect heating and cooling needs are the main factors that drive the amount of energy consumed. Energy prices and government policies can also affect the sources or types of energy consumed.

Sources of GHG emissions estimates

The U.S. Environmental Protection Agency (EPA) publishes estimates for total U.S. GHG emissions to meet annual U.S. commitments under the United Nations Framework Convention on Climate Change (UNFCCC).¹ The U.S. Energy Information Administration (EIA) publishes estimates for energy-related carbon-dioxide (CO₂) emissions—emissions resulting from burning fuel sources for useful energy and non-fuel applications of energy sources—by energy source and by energy-consuming sector by month and year.²

Carbon dioxide

According to EPA, in 2022, CO₂ emissions accounted for about 80% of total gross U.S. anthropogenic GHG emissions (based on 100-year global warming potential). Burning fossil fuels accounted for 74% of total GHG emissions and for 93% of total U.S. anthropogenic CO₂ emissions in the United States. CO₂ emissions from other anthropogenic sources and activities were about 6% of total GHG emissions and 7% of total CO₂ emissions.

Other greenhouse gases

The U.S. and international GHG emissions estimates include several other GHGs that are emitted as a result of human activity:

• Methane (CH₄), which comes from landfills, coal mines, agriculture, and oil and natural gas operations
• Nitrous oxide (N₂O), which comes from using nitrogen fertilizers and burning fossil fuels and certain industrial and waste management processes
• High global warming potential (GWP) gases, which are human-made industrial gases:
  • Hydrofluorocarbons (HFCs)
  • Perfluorocarbons (PFCs)
  • Sulfur hexafluoride (SF₆)
  • Nitrogen trifluoride (NF₃)

The combined emissions of these other greenhouse gases accounted for about 20% of total U.S. anthropogenic GHG emissions in 2022.

The energy connection

Fossil fuels consist mainly of carbon and hydrogen. When fossil fuels are combusted (burned), oxygen combines with carbon to form CO₂ and with hydrogen to form water (H₂O). These reactions release heat, which we use for energy. The amount of CO₂ produced (emitted) depends on the carbon content of the fuel, and the amount of heat produced depends on the carbon and hydrogen content. Because natural gas is mostly methane (CH₄), it has a high hydrogen content, which means burning natural gas produces less CO₂ for the same amount of heat produced from burning other fossil fuels. For example, for the same amount of energy produced, burning natural gas produces about half the CO₂ that burning coal produces.

About half of U.S. energy-related CO₂ emissions were from petroleum use in 2023

In 2023, petroleum accounted for about 38% of U.S. energy consumption, but petroleum was the source of 47% of total annual U.S. energy-related CO₂ emissions. Natural gas accounted for about 36% of U.S. energy consumption and for about 37% of total annual energy-related CO₂ emissions. Coal accounted for about 9% of U.S. energy consumption and for about 16% of total annual energy-related CO₂ emissions.²

The transportation sector accounts for the largest share of U.S. energy-related CO₂ emissions

Consumption of fossil fuels accounts for most of the energy-related CO₂ emissions of the major energy-consuming sectors: commercial, industrial, residential, transportation, and electric power. Although the industrial sector was the highest energy end-use sector in 2023 (includes direct primary energy use and electricity purchases from the electric power sector), the transportation sector emitted more CO₂ because of its near complete dependence on petroleum fuels.

Emissions by the electric power sector can be allocated to each end-use sector according to their respective shares of total annual retail electricity purchases. Even when these electric emissions are apportioned to each sector, the transportation sector accounted for the largest share of U.S. energy end-use CO₂ emissions in 2023.

Natural gas was the highest source of industrial sector CO₂ emissions in 2023, followed by the sector's associated electric emissions, and then by petroleum and coal consumption. Most of the CO₂ emissions associated with energy use by the residential and commercial sectors can be attributed to their associated electric emissions.

The electric power sector accounts for about one third of total U.S. energy-related CO₂ emissions

In 2023, the electric power sector accounted for about 33% of total U.S. primary energy consumption and for about 30% of total U.S. energy-related CO₂ emissions. Natural gas accounted for 50% and coal for 49% of electric power sector CO₂ emissions. Emissions from burning petroleum fuels and non-biomass waste (mainly plastics) in waste-to-energy power plants and emissions from some types of geothermal power plants accounted for about 1% of power sector CO₂ emissions.

Last updated: June 18, 2024; data for 2023 are preliminary.