Meghan Hodges
The United States is one of the world's top polluters, with its historical emissions contributing to global warming. In 2021, the US emitted about 5 billion metric tons of carbon dioxide, accounting for 13.49% of global emissions, more than twice that of all 28 countries in the European Union combined. The country, with just over 4% of the world's population, is responsible for almost a third of the excess carbon dioxide in the atmosphere, mainly due to its heavy reliance on fossil fuels. While the US has made efforts to reduce emissions through initiatives like the Clean Air Act and the Inflation Act, it still faces challenges in sectors such as transportation, agriculture, and energy production, which contribute significantly to greenhouse gas emissions.
| Characteristics | Values |
|---|---|
| Carbon dioxide emissions in 2018 | 81% of all USA greenhouse gases |
| Methane emissions in 2018 | 10% of emitted greenhouse gases |
| Livestock emissions during COVID-19 | 5% of emitted greenhouse gases |
| Carbon dioxide emissions in 2021 | 5 billion metric tons of carbon dioxide per year |
| Percentage of global emissions in 2021 | 13.49% |
| Percentage of global emissions in 2022 | 6,343.2 Million Metric Tons of CO₂ |
| Percentage of direct emissions from transportation | Over 94% |
| Percentage of direct emissions from agriculture | 5% |
| Percentage of total global emissions to maintain a 50% chance of meeting the 1.5°C target | 380 billion metric tons |
| Percentage of total global emissions to maintain a 50% chance of meeting the 2°C target | 1,230 billion metric tons |
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What You'll Learn
The USA's carbon dioxide emissions
Carbon dioxide is released into the atmosphere through the burning of fossil fuels such as coal, natural gas, and oil, as well as trees, solid waste, and biological materials. In 2018, carbon dioxide accounted for approximately 81% of all USA greenhouse gas emissions.
The United States has emitted a quarter of the world's greenhouse gases, more than any other country. In 2020, the US produced 5.2 billion metric tons of carbon dioxide, making it the second-largest emitter after China. That year, the US emitted 11% of the world's greenhouse gases, compared to China's 27%.
The US's carbon dioxide emissions are influenced by various sectors, including residential, commercial, industrial, transportation, and electric power. In 2024, US energy-related CO2 emissions declined by less than 1%, or 23 million metric tons. This decrease was driven by reductions in the residential and industrial sectors. Residential sector emissions decreased due to lower consumption of natural gas and petroleum products for space heating, while industrial sector emissions fell due to reduced manufacturing. Emissions from the commercial, transportation, and electric power sectors remained relatively unchanged.
The US government has implemented various programs and initiatives to reduce carbon dioxide emissions, such as the Regional Greenhouse Gas Initiative (RGGI), a state-level emissions capping and trading program, and the FreedomCAR and Fuel Partnership, which focuses on improving technology for hybrid electric vehicles. Additionally, the US Environmental Protection Agency has established reporting requirements for facilities producing over 25,000 metric tons of carbon dioxide annually, leading to increased transparency and monitoring of greenhouse gas emissions.
Despite these efforts, the US continues to be a major contributor to global carbon dioxide emissions, and its historical emissions have significantly contributed to global warming. According to estimates, to have a 50% chance of limiting global warming to 1.5°C above pre-industrial levels, humanity should limit emissions to no more than 500 billion metric tons. As of 2021, the US was releasing about 5 billion metric tons of carbon dioxide per year, which was about 13.49% of total global emissions.
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The USA's methane emissions
The United States, with just over 4% of the world's population, is responsible for almost a third of the excess carbon dioxide that is heating up the planet. In 2021, the US emitted about 5 billion metric tons of carbon dioxide, contributing to about 13.49% of the total global emissions.
Methane (CH4) is the second most abundant compound of greenhouse gas emissions in the US, after carbon dioxide. In 2022, methane accounted for 12% of all US greenhouse gas emissions from human activities. Methane is emitted from energy, industry, agriculture, land use, and waste management activities.
The largest source of methane emissions in the US is the agricultural sector, including the raising of livestock. The second-largest source is natural gas and petroleum systems, where methane is emitted during the production, processing, storage, transmission, distribution, and use of natural gas, as well as during the production, refinement, transportation, and storage of crude oil. Coal mining is also a source of methane emissions. Landfills are the third-largest source of methane emissions, as waste decomposes and generates methane.
There have been concerns about the underestimation of methane emissions in the US. A 2016 study found that the EPA had underestimated methane emissions by 30 to 50% over at least a decade. Stanford-led research also revealed that methane emissions from a large share of US oil and gas facilities are three times higher than official government estimates. Leaks from these facilities have been identified as a significant contributor to methane emissions, with midstream infrastructure, including pipelines and compressor stations, responsible for about half of the total emissions.
The US government is currently working to reduce methane emissions in various sectors, including agriculture, mining, landfill, and petroleum industries. The EPA's WasteWise program encourages businesses to recycle and reduce waste, while the Regional Greenhouse Gas Initiative (RGGI) is a state-level emissions capping and trading program that includes nine northeastern US states.
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The USA's ozone-depleting emissions
The United States, with just over 4% of the world's population, is responsible for almost a third of the excess carbon dioxide that is heating the planet. The country emits about 5 billion metric tons of carbon dioxide per year, which is about 13.49% of total global emissions. The typical American burns roughly twice as much carbon as the average person in Europe or Japan, and 10 times as much as the average person in India.
The US government uses six "criteria pollutants" as indicators of air quality: ozone, carbon monoxide, sulfur dioxide, nitrogen oxides, particulate matter, and lead. Notably, ozone-depleting substances (ODS) such as chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), halons, methyl bromide, carbon tetrachloride, hydrobromofluorocarbons, chlorobromomethane, and methyl chloroform are not included in these criteria. These ODS are stable in the troposphere and only degrade under intense ultraviolet light in the stratosphere, where they release chlorine or bromine atoms that deplete ozone molecules.
The US has taken steps to reduce ODS emissions, such as through the Clean Air Act and participation in the Montreal Protocol, an international treaty that took effect in 1989. Despite these efforts, a 2016 study found that US methane emissions were underestimated by 30-50% over the last decade. Methane, the second most abundant compound emitted, is mainly produced by livestock and agricultural practices and made up an estimated 10% of emitted greenhouse gases in 2018.
To address climate change, the Regional Greenhouse Gas Initiative (RGGI) was founded in 2007 as a state-level emissions capping and trading program by nine northeastern US states. Additionally, the EPA's WasteWise program encourages businesses to recycle and reduce waste, while the FreedomCAR and Fuel Partnership and Vehicle Technologies Program aim to improve technology for hybrid electric vehicles.
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The USA's vehicle emissions
The United States has been burning coal, oil, and natural gas for far longer than other countries. Despite having just over 4% of the world's population, the country is responsible for almost a third of the excess carbon dioxide that is heating the planet. The typical American burns roughly twice as much carbon as the average person in Europe or Japan and ten times as much as the average person in India.
The transportation sector is the largest source of US greenhouse gas emissions, accounting for 27.2% of the total. Cars and light-duty trucks (including pickups and SUVs) are responsible for 57.5% of transportation emissions. Medium- and heavy-duty vehicles, which include tractor-trailers, large pickups and vans, delivery trucks, buses, and garbage trucks, produce about 26% of transportation emissions.
US vehicle emission standards are set through a combination of legislative mandates enacted by Congress through Clean Air Act (CAA) amendments and executive regulations managed nationally by the Environmental Protection Agency (EPA), and more recently, the National Highway Traffic Safety Administration (NHTSA). These standards cover tailpipe pollution, including carbon monoxide, nitrogen oxides, and particulate emissions, and newer versions have incorporated fuel economy standards.
California has generally been the exception, having been granted a waiver and given the allowance to set stricter standards as it had established its own via the California Air Resources Board (CARB) prior to the 1970 CAA amendments. Several other states have since also received waivers to follow California's standards, which have also become a de facto standard for vehicle manufacturers to follow.
In December 2021, the EPA issued its final rule to revise existing national greenhouse gas emissions standards for passenger cars and light trucks through the model year 2026. The NHTSA issued its fuel economy standards for model year 2024-2026 light-duty vehicles in March 2022. The EPA also released new standards limiting nitrogen oxide (NOx) emissions from heavy-duty trucks in December 2022. Also in 2021, President Biden signed Executive Order 14037, Strengthening American Leadership in Clean Cars and Trucks, which sets a nonbinding target of making 50% of passenger cars and light-duty trucks zero-emission vehicles (ZEVs) by 2030.
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The USA's agricultural emissions
The United States has been burning coal, oil, and natural gas for a long time, and the country, with just over 4% of the world's population, is responsible for almost a third of the excess carbon dioxide heating the planet. In 2021, the US emitted about 5 billion metric tons of carbon dioxide, contributing to about 13.49% of total global emissions.
Agriculture is a significant contributor to the US's greenhouse gas emissions. In 2021, the agricultural sector accounted for 10.6% of US greenhouse gas emissions, emitting 312.6 million metric tons of nitrous oxide (N2O), 278.4 million metric tons of methane (CH4), 44.7 million metric tons of on-farm carbon dioxide (CO2), and 35.7 million metric tons emitted indirectly through electricity use in the agricultural sector. These emissions come from various farming activities, such as fertilizer application, manure storage and management, and enteric fermentation in animals.
The US Environmental Protection Agency (EPA) has reported that agricultural soil management activities, such as the application of synthetic and organic fertilizers, deposition of livestock manure, and growing nitrogen-fixing plants, were the largest contributors to US nitrous oxide emissions in 2022, accounting for 75% of total N2O emissions. Additionally, livestock management, especially ruminants like cattle, contributes to methane emissions through their normal digestive processes, known as enteric fermentation, which represents over a quarter of the agricultural sector's greenhouse gas emissions.
The EPA has also noted that smaller sources of agricultural emissions include carbon dioxide from liming and urea application, methane from rice cultivation, and burning crop residues, which produce methane and nitrous oxide. In 2022, direct greenhouse gas emissions from the agricultural sector accounted for 9.4% of total US greenhouse gas emissions.
It is important to note that the US government has recognized the need to reduce methane emissions in various sectors, including agriculture, and has implemented programs such as the Regional Greenhouse Gas Initiative (RGGI) to cap and trade emissions.
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Frequently asked questions
In 2021, the USA released about 5 billion metric tons of carbon dioxide, which was about 13.49% of total global emissions.
In 2022, the USA's total emissions were 6,343.2 million metric tons.
The USA is responsible for almost a third of the excess carbon dioxide that is heating the planet. The USA and the EU are significant contributors to pollution due to their industrial revolution periods and heavy reliance on fossil fuels.
The transportation sector is the largest source of direct greenhouse gas emissions, with over 94% of the fuel used for transportation being petroleum-based.
