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earth science

Greenhouse gas emissions

Greenhouse gas emissions is a earth science 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 rather than just read about it. In short: Greenhouse gas emissions (GHG emissions) from human activities intensify the greenhouse effect which contributes to climate change. Carbon dioxide (CO2) from burning fossil fuels (such as coal, oil, and natural gas) is the main cause of climate change.

Greenhouse gas emissions — main illustration
Greenhouse gas emissions — illustration

Key takeaways

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

Reference excerpt

Greenhouse gas emissions (GHG emissions) from human activities intensify the greenhouse effect which contributes to climate change. Carbon dioxide (CO2) from burning fossil fuels (such as coal, oil, and natural gas) is the main cause of climate change. The largest annual emissions are from China followed by the United States, which has higher emissions per capita. The main producers fueling the emissions globally are large oil and gas companies. Emissions from human activities have increased atmospheric carbon dioxide by about 50% over pre-industrial levels. The growing levels of emissions have varied, but have been consistent among all greenhouse gases. Over 60 billion tons were emitted in 2025, higher than any year before. Total cumulative emissions from 1870 to 2022 were 703 GtC (2575 GtCO2), of which 484±20 GtC (1773±73 GtCO2) from fossil fuels and industry, and 219±60 GtC (802±220 GtCO2) from land use change. Land-use change, such as deforestation, caused about 31% of cumulative emissions over 1870–2022, coal 32%, oil 24%, and gas 10%. Carbon dioxide is the main greenhouse gas resulting from human activities. It accounts for more than half of warming. Methane (CH4) emissions have almost the same short-term impact. Nitrous oxide (N2O) and fluorinated gases (F-gases) play a lesser role in comparison. Emissions of carbon dioxide, methane and nitrous oxide in 2023 were all higher than ever before. Electricity generation, heat and transport are major emitters; overall energy is responsible for around 73% of emissions. A growing concern for electricity usage is the expansion of artificial intelligence (AI), which is projected to significantly increase global energy demand. Deforestation and other changes in land use also emit carbon dioxide and methane. The largest source of anthropogenic methane emissions is agriculture, closely followed by gas venting and fugitive emissions from the fossil-fuel industry. The largest agricultural methane source is livestock. Agricultural soils emit nitrous oxide partly due to fertilizers. Similarly, fluorinated gases from refrigerants play an outsized role in total human emissions. The current CO2-equivalent emission rates, averaging 4.9 tonnes per person per year, are well over twice the estimated rate of 2.3 tons required to stay within the 2030 Paris Agreement increase of 1.5 °C (2.7 °F) over pre-industrial levels. Annual per capita emissions in the industrialized countries are typically as much as ten times the average in developing countries.

The carbon footprint (or greenhouse gas footprint) serves as an indicator to compare the amount of greenhouse gases emitted over the entire life cycle from the production of a good or service along the supply chain to its final consumption. Carbon accounting (or greenhouse gas accounting) is a framework of methods to measure and track how much greenhouse gas an organization emits. This accounting is used to help understand the various effects of emissions on positive and negative impacts they have on the climate including on human mortality.

Relevance for greenhouse effect and global warming

Overview of main sources

Relevant greenhouse gases

The major anthropogenic (human origin) sources of greenhouse gases are carbon dioxide (CO2), nitrous oxide (N2O), methane and three groups of fluorinated gases (sulfur hexafluoride (SF6), hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs, sulphur hexafluoride (SF6), and nitrogen trifluoride (NF3)). Though the greenhouse effect is heavily driven by water vapor, human emissions of water vapor are not a significant contributor to warming. Although CFCs are greenhouse gases, they are regulated by the Montreal Protocol which was motivated by CFCs' contribution to ozone depletion rather than by their contribution to global warming. Ozone depletion has only a minor role in greenhouse warming, though the two processes are sometimes confused in the media. In 2016, negotiators from over 170 nations meeting at the summit of the United Nations Environment Programme reached a legally binding accord to phase out hydrofluorocarbons (HFCs) in the Kigali Amendment to the Montreal Protocol. The use of CFC-12 (except some essential uses) has been phased out due to its ozone depleting properties. The phasing-out of less active HCFC-compounds will be completed in 2030.

Human activities

Starting about 1750, industrial activity powered by fossil fuels began to significantly increase the concentration of carbon dioxide and other greenhouse gases. Emissions have grown rapidly since about 1950 with ongoing expansions in global population and economic activity following World War II. As of 2021, measured atmospheric concentrations of carbon dioxide were almost 50% higher than pre-industrial levels. The main sources of greenhouse gases due to human activity (also called carbon sources) are:

Burning fossil fuels: Burning oil, coal and gas is estimated to have emitted 37.4 billion tonnes of CO2-eq in 2023. The largest single source is coal-fired power stations, with 20% of greenhouse gases (GHG) as of 2021. Land use change (mainly deforestation in the tropics) accounts for about a quarter of total anthropogenic GHG emissions. Livestock enteric fermentation and manure management, paddy rice farming, land use and wetland changes, human-made lakes, pipeline losses, and covered vented landfill emissions leading to higher methane atmospheric concentrations. Many of the newer style fully vented septic systems that enhance and target the fermentation process also are sources of atmospheric methane. Use of chlorofluorocarbons (CFCs) in refrigeration systems, and use of CFCs and halons in fire suppression systems and manufacturing processes. Agricultural soils emit nitrous oxide (N2O) partly due to application of fertilizers. The largest source of anthropogenic methane emissions is agriculture, closely followed by gas venting and fugitive emissions from the fossil-fuel industry. The largest agricultural methane source is livestock. Cattle (raised for both beef and milk, as well as for inedible outputs like manure and draft power) are the animal species responsible for the most emissions, representing about 65% of the livestock sector's emissions.

Global estimates

… excerpt ends here. Continue reading the full article.

Illustrations

Greenhouse gas emissions: Greenhouse gas emissions per person in the highest-emitting countries.[1] Areas of rectangles represent total emissions for each country.
Greenhouse gas emissions per person in the highest-emitting countries.[1] Areas of rectangles represent total emissions for each country.
Greenhouse gas emissions: The industrial era growth in atmospheric CO2-equivalent gas concentrations since 1750[34]
The industrial era growth in atmospheric CO2-equivalent gas concentrations since 1750[34]
Greenhouse gas emissions: Per capita CO2 emissions surged after the mid-20th century, but then slowed their rate of growth.[45]
Per capita CO2 emissions surged after the mid-20th century, but then slowed their rate of growth.[45]
Greenhouse gas emissions: Scaling the effect of wealth to the national level: richer (developed) countries emit more CO2 per person than poorer (developing) countries.[54] Emissions are roughly proportional to GDP per person, though the rate of increase diminishes with average GDP/pp of about $10,000.
Scaling the effect of wealth to the national level: richer (developed) countries emit more CO2 per person than poorer (developing) countries.[54] Emissions are roughly proportional to GDP per person, though the rate of increase diminishes with average GDP/pp of about $10,000.
Greenhouse gas emissions: Substantial land-use change contributions to emissions have been made by Latin America, Southeast Asia, Africa, and Pacific Islands. Area of rectangles shows total emissions in 2019 for that region.[59]
Substantial land-use change contributions to emissions have been made by Latin America, Southeast Asia, Africa, and Pacific Islands. Area of rectangles shows total emissions in 2019 for that region.[59]

Worked examples

Example 1 — a first encounter with Greenhouse gas emissions

Start with the simplest possible case. Write down what Greenhouse gas emissions claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, 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 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 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

In research
Greenhouse gas emissions appears in earth science 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 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 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Climate change, Climate forcing, Greenhouse gas emissions, so understanding it makes those chapters shorter.
In everyday life
Look for Greenhouse gas emissions 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 in 20 minutes

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

Frequently asked questions

What is Greenhouse gas emissions in simple terms?

Greenhouse gas emissions (GHG emissions) from human activities intensify the greenhouse effect which contributes to climate change. Carbon dioxide (CO2) from burning fossil fuels (such as coal, oil, and natural gas) is the main cause of climate change.

Why does Greenhouse gas emissions matter?

Because it connects several earth science 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?

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.

Tags

  • Climate change
  • Climate forcing
  • Greenhouse gas emissions

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