Did you know?
Fossil fuels are the source of about 80% of U.S. primary energy use and the source of about 75% of total greenhouse gas emissions.
In the United States, most of the emissions of human-caused (anthropogenic) greenhouse gases (GHG) come primarily from burning fossil fuels (coal, hydrocarbon gas liquids, 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.
In 2015, emissions of carbon dioxide (CO2) resulting from the combustion of fossil fuels for energy were equal to 77% of total U.S. anthropogenic GHG emissions (based on global warming potential) and about 93% of total U.S. anthropogenic CO2 emissions. Carbon dioxide emissions from other anthropogenic sources and activities were about 5% of total GHG emissions and about 7% of total CO2 emissions.1
Other greenhouse gases
The U.S. and international GHG emissions estimates include several other GHG 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, burning fossil fuels, and using 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 gases accounted for about 18% of total U.S. anthropogenic GHG emissions in 2015.
The energy connection
Fossil fuels consist mainly of carbon and hydrogen. When fossil fuels are burned, oxygen combines with carbon to form CO2 and with hydrogen to form water (H2O). These reactions release heat that we use for energy. The amount of CO2 produced depends on the carbon content of the fuel, and the amount of heat produced depends on the carbon and hydrogen content. Because natural gas, which is mostly methane (CH4), has a high hydrogen content, combustion of 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 of the amount of CO2 produced by burning coal.
About half of U.S. energy-related CO2 emissions are from petroleum use
In 2016, about 45% of U.S. energy-related carbon dioxide emissions came from burning petroleum fuels, 29% came from burning natural gas, and 28% came from burning coal.2 Although the industrial sector is the largest consumer of energy (including direct fuel use and electricity purchased from the electric power sector), the transportation sector emits more CO2 because of its near complete dependence on petroleum fuels.
The residential sector and the commercial sector have lower CO2 emission levels than the transportation sector and the industrial sector. Most of the CO2 emissions associated with energy use by the residential and commercial sectors are from fossil fuel combustion by the electric power sector, which produces the electricity that the residential and commercial sectors purchase from electric utilities.
Coal is the dominant CO2 emissions source related to electricity generation
In 2016, the electric power sector accounted for about 39% of U.S. primary energy consumption and produced 35% of total U.S. energy-related CO2 emissions. Coal accounted for 68% and natural gas for 30% of the CO2 emissions from the electric power sector.