Greenhouse gas emissions by the United States

The United States was one of the world's largest emitters of greenhouse gases (GHGs), emitting roughly 6,343.2 million metric tons of carbon dioxide and equivalents in 2022, up from 5,222 million metric tons in 2020. At the same time, the country has been the largest historical emitter of GHGs, releasing more into the atmosphere through human activity than any other country in history. Some of the most common greenhouse gases—gases that trap heat inside Earth’s atmosphere—are carbon dioxide, methane, and nitrous oxide. Human activity, such as burning fossil fuels and cutting down trees, has greatly increased the concentration of greenhouse gases in the atmosphere. Scientists believe that higher GHG concentrations are responsible for causing climate change, which is the long-term shift of Earth’s temperature and climate patterns.

Since the United States had the highest historical greenhouse gas output in the early 2020s, many people believed it should take on a central role in the global fight to reduce the negative effects of climate change, which had already caused economic instability and social unrest in some parts of the world.

Overview

Types and Sources of Greenhouse Gases

When released into the atmosphere, greenhouse gases cause Earth to warm. Some GHGs occur naturally, such as carbon dioxide, methane, and nitrous oxide. However, others are not found in nature and have been created by humans. For example, people make sulfur hexafluoride to use in electric systems and other applications. Sulfur hexafluoride is the world’s most potent GHG, which means that it can trap the most radiation in the atmosphere. However, Earth’s atmosphere contains a much lower concentration of this gas than other GHGs, such as carbon dioxide. Therefore, other greenhouse gases have a more significant impact on climate change than sulfur hexafluoride.

Human activity is the only way human-made GHGs, such as sulfur hexafluoride, enter the atmosphere. However, naturally occurring GHGs are in the atmosphere because of human activity and biochemical processes in nature, such as photosynthesis, respiration, and decomposition. These processes help the gases cycle between the environment and the atmosphere. For example, trees and other plants sequester, or trap, atmospheric carbon dioxide to use during photosynthesis. However, after a tree dies and begins to decompose, it emits some of its carbon back into the atmosphere, so cutting down trees and clearing land contribute to climate change. Other human activities also affect greenhouse gas concentrations in the atmosphere. For example, people produce carbon dioxide by burning fossil fuels.

Fortunately, people can also take actions to reduce GHGs in the atmosphere. For example, they can plant trees, which sequester carbon dioxide.

Human Greenhouse Gas Emissions

The concentrations of atmospheric greenhouse gases such as carbon dioxide, methane, and nitrous oxide have increased dramatically since the 1700s. Atmospheric carbon dioxide increased from roughly 280 parts per million (ppm) in the mid-1700s to roughly 415 ppm in 2021. Although the concentration of carbon dioxide can be affected by natural processes and human actions, scientists believe that human activity is responsible for the dramatic increase in the gas since the 1700s; they have found a strong correlation between the rise in atmospheric carbon dioxide levels and the rise in human carbon dioxide emissions. Also, from the 1700s to 2021, atmospheric methane concentrations nearly tripled, reaching roughly 1,900 parts per billion (ppb) in 2021 (Tollefson, 2022).

Human GHG emissions were extremely limited until the mid-1700s. At that time, the Industrial Revolution reshaped societies worldwide by steering them away from agrarian economies and toward those driven by mechanical manufacturing and industry. During the Industrial Revolution, people began burning coal and other fossil fuels, which emitted carbon dioxide and other greenhouse gases into the atmosphere. These emitted gases built up over decades, causing climate change.

Although the concentration of carbon dioxide and other GHGs increased significantly from the 1700s to the 2000s, only a few countries are responsible for most of the emissions that fueled the increase. At the beginning of the Industrial Revolution, the United Kingdom (UK) was the largest emitter of carbon dioxide. In 1850, the UK produced six times as much carbon dioxide as the next-largest producer, the United States. In roughly 1911, the United States overtook the UK in carbon dioxide production. The United States remained the top producer of carbon dioxide emissions until 2006, when China surpassed it.

Greenhouse Gas Emissions in the United States

In 2020, the United States emitted 5,222 million metric tons of carbon dioxide (after accounting for sequestrations; “Inventory of U.S.,” 2022). The 2020 emissions were roughly 21 percent lower than the country’s emissions in 2005 and about 7 percent lower than in 1990. This decline occurred for numerous reasons, including improved technology, economic changes, and population changes, but primarily, emissions were lower in 2020 because of the COVID-19 pandemic. However, in 2022, US emissions reached 6,343.2 million metric tons of carbon dioxide, which was a decrease of only 3 percent from 1990 levels.

Behind China, the United States is the world's second-largest producer of carbon dioxide. In 2022, carbon dioxide made up approximately 80 percent of the United States’ total greenhouse gas emissions. In 2022, burning fossil fuels to generate electricity accounted for about 30 percent of the United States' carbon dioxide emissions and 24 percent of the nation's total emissions. The United States also emitted carbon dioxide through cement production and other industrial processes. Carbon dioxide was also the greenhouse gas with the largest decrease in production between 2005 and 2020 in the United States. This reduction was caused in part by the country’s pivot from coal to natural gas as a fuel for electricity production, as burning natural gas produces less carbon dioxide than burning coal. Land use in the United States also affects net carbon dioxide emissions, with long-term forests sequestering more carbon than other land uses. However, as COVID-19 pandemic restrictions were lifted and patterns of life returned to normal, emissions spiked, exceeding pre-pandemic levels.

The next most-abundant greenhouse gas produced globally, and in the US, is methane, which made up roughly 11 percent of the country’s greenhouse gas production in the early and mid-2020s. The agricultural industry (also called the land use, land-use change, and forestry sector, or LULUCF) was one of the largest contributors to methane emissions. Livestock, including cattle and sheep, produce methane as part of their digestive processes. The energy industry is also responsible for a significant portion of the United States’ methane emissions. Methane is a component of natural gas and escapes into the atmosphere when natural gas is produced, transported, and used (“Overview of greenhouse gases,” 2022).

Nitrous oxide made up roughly 6 percent of US greenhouse gas emissions in 2022. The country produced nitrous oxide through agriculture, industrial processes, energy production, and other industries. Roughly 75 percent of the United States’ nitrous oxide production came from its agricultural sector. Nitrogen is cycled out of the atmosphere during the nitrogen cycle, mostly by bacteria that break down the substance in soil and the ocean. The United States reduced its nitrous oxide production by about 3 percent from 1990 to 2022.

About 3 percent of the GHGs in the United States produced in 2020 were fluorinated gases. Between 1990 and 2022, the United States increased its production of fluorinated gases by about 105 percent. This occurred when the US government limited ozone-depleting substances (ODSs), such as chlorofluorocarbons (CFCs). People substituted CFCs and other ODSs with fluorinated gases. Unlike many GHGs, fluorinated gases are produced only by human activity and have no natural source.

Sources of Greenhouse Gas Emission in the United States

Various industries and economic sectors contribute to the United States’ greenhouse gas emissions, and the gases they produce differ. The economic sectors that produced the most GHGs in the early and mid-2020s were transportation, electricity generation, industry, agriculture, and homes and businesses.

Transportation was the sector with the highest contribution of GHGs in the United States in 2022, contributing roughly 28 percent of all GHGs produced by the country that year. This was largely because of the industry’s reliance on petroleum-based fuels. The transportation sector moves people and goods by car, truck, train, ship, plane, and other vehicles. Carbon dioxide was the most produced greenhouse gas by the transportation industry, which increased as demand for travel and the use of larger vehicles rose. The US government increased fuel-efficiency requirements at that time, and this change helped reduce the overall increase in carbon dioxide emissions from this sector. The transportation industry emitted relatively small amounts of methane and nitrous oxide in 2020 (“Inventory of US,” 2022).

The electrical generation sector contributed about 25 percent of the United States’ greenhouse gas emissions in 2022. The total emissions from this sector decreased by about 15 percent from 1990 to 2022, in part due to increased use of renewable energy sources. In 1990, nearly all the power in the United States was generated by burning fossil fuels. Furthermore, using natural gas in place of coal, which produces more carbon dioxide than natural gas, helped reduce carbon dioxide emissions.

The industrial sector accounted for about 23 percent of total US greenhouse gas emissions in 2022. Industrial sector emissions in the United States decreased by about 22 percent between 1990 and 2022, mainly due to changes in fuel types, particularly the replacement of coal with natural gas. This reduction also occurred because of changes in the US economy, such as in the manufacturing sector, which began making materials and products that required less energy to produce.

The agricultural sector (also called the land use, land-use change, and forestry sector, or LULUCF) contributed about 13 percent of the United States’ GHGs in 2022. Contributing to this sector’s greenhouse gas emissions were manure management, livestock production, and soil management (e.g., through chemical fertilizers). The agricultural sector was the largest producer of nitrous oxide in the early and mid-2020s; worsening this issue, carbon sequestration from this sector declined by 11 percent between 1990 and 2022.

Businesses and homes, or the commercial and residential sectors, produced roughly 7 and 6 percent, respectively, of the total GHGs created in the United States in 2020. The commercial and residential sectors increased overall greenhouse gas production from 1990 to 2020. Annual fluctuations are common in these sectors, as changing weather conditions affect the demand for heating fuel.

Further Insights

When greenhouse gas emissions from human activities increase, they accumulate in the atmosphere, contributing to the greenhouse effect. This process is fueled by energy from the sun. Earth receives the sun’s energy through visible light, ultraviolet radiation, and infrared radiation. Most of the sun’s energy is in the form of infrared radiation, which fuels Earth’s climate system and warms the planet. Greenhouse gases act like a blanket around Earth, keeping the heat energy trapped in the atmosphere. Therefore, an increase in atmospheric GHGs leads to an increase in Earth’s temperature. Furthermore, GHGs can make it easier for more infrared radiation to reach Earth’s surface. Since energy fuels Earth’s climate systems, an increase in atmospheric energy will cause the climate to change.

Earth’s climate system consists of many interrelated components. When one component changes, it often affects other components in the system. For example, an increase in temperature can reduce the amount of snow cover on land. White snow reflects more radiation than darker land, so when the snow melts, Earth’s surface absorbs more heat and becomes even hotter.

Climate change has occurred in the past, with changes in atmospheric GHGs making Earth colder or warmer. Climate change can greatly alter life on Earth by affecting weather patterns (including extreme temperatures and storms) and sea levels. Many organizations, governments, and individuals want to limit the amount of greenhouse gases that human activities are allowed to release into the atmosphere.

Viewpoints

Scientists discovered that greenhouse gases were a threat to the environment in the 1960s. At that time, some scientists began predicting that a warming planet could lead to climate change. By the 1990s, most scientists, governments, and organizations worldwide asserted that reducing greenhouse gas emissions was necessary to prevent the most catastrophic effects of climate change. In 1992, countries around the world, including the United States, joined the United Nations Framework Convention on Climate Change, which called for reductions in greenhouse gas emissions. In the late 1990s, most countries signed the Kyoto Protocol, which also called for reducing greenhouse gas emissions. The United States was one of the few developed nations that refused to adopt the protocol. However, in 2015, the country adopted the Paris Agreement (PA), another international treaty that set standards for countries to follow to reduce greenhouse gas emissions and mitigate the harm caused by climate change. However, two years later, in 2017, newly elected US President Donald Trump withdrew the United States from the treaty. Although President Joe Biden reentered the PA in 2021, the country had already faced criticism for its intention to exit.

Although the United States was no longer the largest carbon dioxide emitter by the 2010s, it was still the largest historical carbon dioxide emitter. By the 2020s, the United States had produced roughly 20 to 25 percent of the total carbon dioxide emissions ever created by human activity. The next-largest historical emitter was China, which had produced roughly 10 to 15 percent of all carbon dioxide emissions.

The United States’ historic contributions to greenhouse gas emissions and its reluctance to join the international community in reducing them drew heavy criticism from climate activists, climate scientists, and leaders of other governments. The United States faced particularly harsh criticism because it had emitted historic levels of GHGs to build its own economy, while many other countries could not use fossil fuels to rapidly expand their economies.

Those who support climate justice initiatives often assert that countries like the United States, whose economies greatly benefited from record-breaking greenhouse gas emissions, should lead global efforts to reduce emissions and stop using fossil fuels first, before developing nations.

A 2020 poll from the Pew Research Center found that most Americans (65 percent) believed the US government should do more to address climate change (Tyson, A., & Kennedy, 2020). Yale University's 2024 Climate Change in the American Mind survey supported this finding, reporting that 55 percent of registered voters agreed that the government should do more to protect people from the negative health impacts of climate change. However, notably, 20 percent responded that efforts should remain at the current levels, and 15 percent stated that efforts should be reduced. In 2025, as Donald Trump began his second term as president, the nation announced its intention to withdraw from the Paris Agreement, increase fossil fuel production, and reverse numerous existing climate laws and regulations. Critics noted that this shift could have detrimental environmental consequences as the nation's total emissions increase.

Bibliography

Climate change indicators: Atmospheric concentrations of greenhouse gases. (2021, July 21). United States Environmental Protection Agency. Retrieved January 22, 2026, from https://19january2021snapshot.epa.gov/climate-indicators/climate-change-indicators-atmospheric-concentrations-greenhouse-gases_.html

The greenhouse effect and our planet. (2022, July 19). National Geographic. Retrieved January 22, 2026, from https://education.nationalgeographic.org/resource/greenhouse-effect-our-planet

Inventory of U.S. greenhouse gases emissions and sinks. (2022). United States Environmental Protection Agency. Retrieved January 22, 2026, from https://www.epa.gov/system/files/documents/2022-04/us-ghg-inventory-2022-main-text.pdf

Lindsey, R. (2025, May 21). Climate change: atmospheric carbon dioxide . National Oceanic and Atmospheric Administration. Retrieved January 22, 2026, from https://www.climate.gov/news-features/understanding-climate/climate-change-atmospheric-carbon-dioxide

Overview of greenhouse gases. (2025, December 29). United States Environmental Protection Agency. Retrieved January 22, 2026, from https://www.epa.gov/ghgemissions/overview-greenhouse-gases

Sources of greenhouse gas emissions. (2025, March 31). United States Environmental Protection Agency. Retrieved January 22, 2026, from https://www.epa.gov/ghgemissions/sources-greenhouse-gas-emissions

Tollefson, J. (2022, February 8). Scientists raise alarm over ‘dangerously fast’ growth in atmospheric methane. Nature. Retrieved January 22, 2026, from https://www.nature.com/articles/d41586-022-00312-2

Tyson, A., & Kennedy, B. (2020, June 23). Two-thirds of Americans think the government should do more on climate. Pew Research Center. Retrieved January 22, 2026, from https://www.pewresearch.org/science/2020/06/23/two-thirds-of-americans-think-government-should-do-more-on-climate

Van Houtan, K. S. (2021). The geographic disparity of historical greenhouse emissions and projected climate change. Science Advances, 7(29). Retrieved January 22, 2026, from https://doi.org/10.1126/sciadv.abe4342