physics

Greenhouse gas emissions by the United States

Greenhouse gas emissions by the United States is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Greenhouse gas emissions by the United States rather than just read about it. In short: The United States produced 7 billion metric tons of carbon dioxide equivalent greenhouse gas (GHG) emissions in 2025, the second largest in the world after greenhouse gas emissions by China and among the countries with the highest greenhouse gas emissions per person. In 2025 China is estimated to have emitted 29% of world GHG, followed by the United States with 12%, then India with 7%.

Key takeaways

Greenhouse gas emissions by the United States belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Greenhouse gas emissions by the United States to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Greenhouse gas emissions by the United States from memory before moving on to harder problems.

Reference excerpt

The United States produced 7 billion metric tons of carbon dioxide equivalent greenhouse gas (GHG) emissions in 2025, the second largest in the world after greenhouse gas emissions by China and among the countries with the highest greenhouse gas emissions per person. In 2025 China is estimated to have emitted 29% of world GHG, followed by the United States with 12%, then India with 7%. In total the United States has emitted a quarter of world GHG, more than any other country. Annual emissions are over 15 tons per person and, amongst the top eight emitters, it is the highest country by greenhouse gas emissions per person. The IEA estimates that the richest decile in the US emits over 55 tonnes of CO2 per capita each year. Because coal-fired power stations are gradually shutting down, in the 2010s emissions from electricity generation fell to second place behind transportation which is now the largest single source. In 2020, 27% of the GHG emissions of the United States were from transportation, 25% from electricity, 24% from industry, 13% from commercial and residential buildings and 11% from agriculture. U.S. energy-related CO2 emissions decreased by 3% in 2023, amounting to a reduction of approximately 134 million metric tons (MMmt). This reduction primarily occurred in the electric power sector, with a significant shift from coal-fired power to less carbon-intense fossil fuels such as natural gas, as well as sustainable energy sources like solar. In 2021, the electric power sector was the second largest source of U.S. greenhouse gas emissions, accounting for 25% of the U.S. total. U.S. greenhouse gas emissions are contributing to climate change in the United States, as well as worldwide.

Background

In context of climate change

Greenhouse gases absorb radiant energy from the Earth after the surface is warmed by sunlight. US emissions in 2022 involved carbon dioxide (CO2, 79.7%), methane (CH4, 11.1%), nitrous oxide (N2O, 6.1%) and other gases (e.g., fluorinated gases, 3.1%). Greenhouse gases vary in how long they remain in the atmosphere. Though methane and nitrous oxide are more potent greenhouse gasses than CO2, CO2 is longer-lived, remaining in the atmosphere for centuries. The average CO2 concentration in 2024 was over 424 parts per million (ppm), and exceeded 427 ppm in February 2025—each more than 50% higher than its pre-industrial level. Annual US national CO2 emissions were exceeded only by those of China, which has four times the US population. Regardless of where emissions occur, the emitted gases spread around the world. This anthropogenic (human-caused) increase in greenhouses gases has impacts on weather patterns, droughts, heat waves, wildfires, ocean acidification, sea level rise, glacial melting, average global temperatures, extinction of species, and so forth.

Sources of greenhouse gases Carbon dioxide enters the atmosphere through the mass burning of fossil fuels such as coal, natural gas, and oil along with trees, solid waste, and biological materials. In 2018, carbon dioxide was estimated to approximately be 81% of all USA greenhouse gases emitted in 2018. Natural sinks and reservoirs absorb carbon dioxide emissions through a process called the carbon cycle. Sinks and reservoirs can include the ocean, forests and vegetation, and the ground. Methane is mainly produced by livestock and agricultural practices. Methane was estimated to make up 10% of emitted greenhouse gases. From the decrease in non-agricultural GHG emissions during COVID-19, the percent of the USA's GHG emissions from livestock increased from 2.6% to about 5%, which is a smaller percentage than many other countries likely because the USA has more greenhouse gas emissions from vehicles, machines, and factories. Nitrous oxide is a greenhouse gas produced mainly by agriculture. Fluorinated gases are synthetically produced and used as substitutes for stratospheric ozone-depleting substances. Greenhouse gases are produced from a wide variety of human activities, though some of the greatest impacts come from burning fossil fuels, deforestation, agriculture and industrial manufacturing. In the United States, power generation was the largest source of emissions for many years, but in 2017, the transportation sector overtook it as the leading emissions source. As of that year, the breakdown was transportation at 29%, followed by electricity generation at 28% and industry at 22%. After carbon dioxide, the next most abundant compound is methane, though there have been methodological differences in how to measure its effects. According to a 2016 study, US methane emissions were underestimated by the EPA for at least a decade, by some 30 to 50 percent. Another area of concern is that of ozone-depleting substances such as chlorofluorocarbons (CFCs) and hydrofluorocarbons (HFCs), which are often potent greenhouse gases with serious global warming potential (GWP). However, significant progress has been made in reducing the usage of these gases as a result of the Montreal Protocol, the international treaty that took effect in 1989.

Major emissions-creating events In February 2018, an explosion and blowout in a natural gas well in Belmont County, Ohio was detected by the Copernicus Sentinel-5P satellite's Tropospheric Monitoring Instrument. The well was owned by XTO Energy. About 30 homes were evacuated, and brine and produced water were discharged into streams flowing into the Ohio River. The blowout lasted 20 days, releasing more than 50,000 tons of methane into the atmosphere. The blowout leaked more methane than is discharged by most European nations in a year from their oil and gas industries.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Greenhouse gas emissions by the United States

Start with the simplest possible case. Write down what Greenhouse gas emissions by the United States claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Greenhouse gas emissions by the United States before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Greenhouse gas emissions by the United States ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Greenhouse gas emissions by the United States

In research: Greenhouse gas emissions by the United States appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Greenhouse gas emissions by the United States in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Greenhouse gas emissions by the United States is common in secondary-school and first-year university syllabi. It links to neighbouring topics Energy in the United States, Greenhouse gas emissions in the United States, Low-carbon economy, so understanding it makes those chapters shorter.
In everyday life: Look for Greenhouse gas emissions by the United States outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Greenhouse gas emissions by the United States in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Greenhouse gas emissions by the United States means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Greenhouse gas emissions by the United States out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Greenhouse gas emissions by the United States in simple terms?

Why does Greenhouse gas emissions by the United States matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Greenhouse gas emissions by the United States?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Greenhouse gas emissions by the United States.