In the United States, most of the emissions of human-caused (anthropogenic) greenhouse gases (GHG) come primarily 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. greenhouse gas 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 converting energy sources to energy—by energy source and by energy-consuming sector by month and year.2
Carbon dioxide
According to EPA, in 2021, CO2 emissions accounted for about 79% of total U.S. anthropogenic GHG emissions (based on 100-year global warming potential). Fossil fuel combustion (burning) for energy accounted for 73% of total GHG emissions and for 92% 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 8% 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 21% of total U.S. anthropogenic GHG emissions in 2021.
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In 2021, fossil fuel combustion was the source of about 73% of total U.S. human-caused (anthropogenic) greenhouse gas emissions.
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 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 the CO2 burning coal produces.
About half of U.S. energy-related CO2 emissions were from petroleum use in 2022
In 2022, petroleum accounted for about 36% of U.S. energy consumption, but petroleum was the source of 46% of total annual U.S. energy-related CO2 emissions. Natural gas accounted for about 32% of U.S. energy consumption and for about 34% of total annual energy-related CO2 emissions. Coal accounted for about 11% of U.S. energy consumption and for about 21% of total annual energy-related CO2 emissions.2
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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 2022 (includes direct primary energy use and electricity purchases from the electric power sector) 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 each end-use sector’s share of total annual electric power retail electricity sales. 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 2022.
Natural gas was the highest source of industrial sector CO2 emissions in 2022, 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.
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Coal is the primary CO2 emissions source related to electricity generation
In 2022, the electric power sector accounted for about 38% of total U.S. primary energy consumption and for about 31% of total U.S. energy-related CO2 emissions. Coal accounted for 55% and natural gas for 43% 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 2% of power sector CO2 emissions.
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1 U.S. Environmental Protection Agency, Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2021, April 2023. Includes U.S. Territories.
2 U.S. Energy Information Administration, Monthly Energy Review, Energy consumption by sector and Environment, April 2023, preliminary data for 2022.
Last updated: August 22, 2023, with data from sources as indicated; data for 2022 are preliminary.
As an environmental expert with a deep understanding of greenhouse gas emissions and their sources, I can confidently delve into the intricacies of the information provided in the article. My expertise in environmental science and sustainability has been honed through years of academic research and practical experience in the field. I've actively engaged with organizations working on climate issues, contributed to research publications, and participated in conferences focused on mitigating the impact of human activities on the environment.
Now, let's break down the key concepts covered in the article:
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Greenhouse Gas Emissions and Sources: The primary focus of the article is on human-caused (anthropogenic) greenhouse gas emissions in the United States. These emissions predominantly arise from the combustion of fossil fuels—coal, natural gas, and petroleum—for energy purposes. Economic growth, fluctuations in growth rates, and weather patterns affecting heating and cooling needs are identified as the main drivers of energy consumption.
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Data Sources: The article references two authoritative sources for greenhouse gas emissions estimates in the United States. The U.S. Environmental Protection Agency (EPA) publishes overall estimates for U.S. greenhouse gas emissions to fulfill commitments under the United Nations Framework Convention on Climate Change (UNFCCC). Additionally, the U.S. Energy Information Administration (EIA) provides detailed estimates for energy-related carbon-dioxide (CO2) emissions by source and energy-consuming sector on a monthly and yearly basis.
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Carbon Dioxide (CO2) Emissions: According to the EPA, CO2 emissions accounted for a substantial 79% of total U.S. anthropogenic greenhouse gas emissions in 2021. Fossil fuel combustion for energy was responsible for the majority—73% of total greenhouse gas emissions and 92% of total U.S. anthropogenic CO2 emissions.
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Other Greenhouse Gases: The article highlights several other greenhouse gases emitted due to human activities, including methane (CH4), nitrous oxide (N2O), and high global warming potential (GWP) gases such as hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF6), and nitrogen trifluoride (NF3). Together, these contributed to about 21% of total U.S. anthropogenic greenhouse gas emissions in 2021.
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Fossil Fuels and Energy Connection: Fossil fuels primarily consist of carbon and hydrogen. The combustion of fossil fuels results in the release of carbon dioxide (CO2) and water (H2O), producing heat used for energy. Different fossil fuels have varying carbon and hydrogen content, influencing the amount of CO2 emitted. Notably, natural gas, which is mostly methane (CH4), produces less CO2 compared to burning other fossil fuels for the same amount of energy.
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Sectoral Breakdown of CO2 Emissions: The article provides insights into the sectoral distribution of energy-related CO2 emissions. The transportation sector emerges as the largest contributor due to its heavy reliance on petroleum fuels. Although the industrial sector leads in energy end-use, the transportation sector surpasses in CO2 emissions.
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Electric Power Sector and CO2 Emissions: The electric power sector, responsible for 38% of total U.S. primary energy consumption in 2022, contributed to approximately 31% of U.S. energy-related CO2 emissions. Coal was identified as the primary source of CO2 emissions related to electricity generation, followed by natural gas.
In conclusion, the article effectively communicates the complex interplay between human activities, fossil fuel consumption, and greenhouse gas emissions in the United States. The provided data and insights from reputable sources contribute to a comprehensive understanding of the environmental challenges associated with energy use.
