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A Guide to Greenhouse Gases: Examples, Causes, Effects, and More

September 21, 2022
Time to read: 10 minutes
Credit: John Hogg/World Bank

The amount of greenhouse gases in the atmosphere has skyrocketed since the Industrial Revolution, causing concerns about global warming, climate change, and carbon footprints. Animal agriculture, deforestation, transportation, and the production of electricity have all contributed to this problem, but what can be done to solve it? This article aims to explain what greenhouse gases are, their causes, their effects, and what can be done to lower their emissions.

What Are Greenhouse Gases?

Greenhouse gases are gases that trap heat in the Earth’s atmosphere, leading to increased temperatures. The most common greenhouse gases are carbon dioxide, methane, nitrous oxide, and fluorinated gases, including hydrofluorocarbons, perfluorocarbons, sulfur hexafluoride, and nitrogen trifluoride. Water vapor is also considered a greenhouse gas, but because its increased atmospheric concentrations are not caused by humans and are a consequence of global warming, rather than a cause, it will not be discussed in this article.

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How Do Greenhouse Gases Heat the Earth?

The Sun’s energy reaches Earth mostly as light, which is made of photons that have a certain amount of energy. This energy then leaves Earth as infrared radiation, or heat. Greenhouse gas molecules, however, absorb some of this energy, preventing it from leaving the atmosphere. Eventually, the greenhouse gas molecules release the energy, which can either remain trapped in Earth’s atmosphere by other greenhouse gas molecules or continue out into space. When the energy stays trapped, it does so as infrared radiation, causing increased temperatures. This process of greenhouse gases reflecting infrared radiation back into the atmosphere is called the “greenhouse effect” because it traps heat like the glass of a greenhouse.

How Are Greenhouse Gases Measured?

Because there are multiple greenhouse gases, scientists and policy makers need a way to compare them. This is usually done using a gases’s Global Warming Potential. This conversion factor accounts for two key differences among greenhouse gases: how long they stay in the atmosphere, or their lifetime, and how well they absorb energy, or their radiative efficiency. According to the EPA, it compares gases by measuring “how much energy the emissions of one ton of a gas will absorb over a given period of time, relative to the emissions of one ton of carbon dioxide.” 

This means that, by definition, carbon dioxide has a Global Warming Potential of one, no matter the time period. The most common time period used for other greenhouse gases is 100 years. Methane has an estimated Global Warming Potential of 30 over 100 years because while it has a shorter lifetime than carbon dioxide, it has a much higher radiative efficiency. Nitrous oxide has a lifetime of over 100 years on average, and therefore has an estimated Global Warming Potential of 273 over 100 years. The Global Warming Potentials for fluorinated gases varies but can be in the thousands or tens of thousands because of their extremely high radiative efficiency.

While Global Warming Potential is by far the most commonly used measurement of greenhouse gases, the conversion factor is not perfect. A recent study has suggested adopting a new method because Global Warming Potential may underestimate the effect of methane, with another study finding that methane may be four times as sensitive to global warming than previously thought.

Why Are Greenhouse Gases So Bad?

The greenhouse effect is not entirely a problem. A well-balanced atmosphere of greenhouse gases is necessary to keep Earth warm enough to support life. However, human activity is causing more greenhouse gas emissions, which increases the greenhouse effect unnaturally, leading to abnormally high temperatures. This causes climate change

The effects of climate change are numerous. Extreme weather events such as heat waves, hurricanes, and precipitation changes leading to droughts or floods increase in frequency and intensity. Sea levels rise because of melting glaciers and icebergs, as well as higher ocean temperatures. Ecosystems and habitats are altered, disrupting species’ abundance, geographic ranges, seasonal activities, and migration patterns. In addition to wildlife, humans are harmed due to the increased spread of diseases, heat-related illnesses and deaths, and food insecurity as agriculture fails to respond to the extreme weather changes. his instability can also cause mass migration and political unrest, further harming humans.

How Have Humans Contributed to Greenhouse Gas Emissions?

Emissions by sector – pie charts

There is a clear and broad consensus in the scientific community that human activity has been the main driver of climate change since the 1800’s. This figure depicts sources of anthropogenic greenhouse gas emissions, as of 2016.


Energy is the sector producing the most global greenhouse emissions. The combustion of fossil fuels, such as coal, oil, and natural gas, produces the energy much of our world is dependent on, but also releases large amounts of carbon dioxide, as well as some methane and nitrous oxide. 

Most of this energy is used for manufacturing to power industrial buildings and machinery. Some of these fossil fuels are needed to produce electricity for commercial and residential buildings. Energy is also needed to power buildings and machinery necessary for agriculture and fishing. On factory farms, feed requires about 75 percent of the total energy input, and the other 25 percent is used for heating, lighting, and ventilation of buildings. Finally, leaks during energy production, such as coal mining and oil and gas extraction and transportation, are responsible for almost six percent of global greenhouse emissions.

Animal Agriculture and Land Use

Agriculture is the largest contributor of global greenhouse gas emissions after the energy sector. Animal agriculture alone is responsible for around 15.4% of global greenhouse gas emissions—approximately equivalent to the emissions from the entire transportation sector. Farmed animals release methane through enteric fermentation, in which the microbes in the digestive systems of ruminant animals breakdown and ferment plant material, creating methane as a byproduct. Ruminant animals include cows, goats, sheep, and buffalo, but cows are by far the largest source of animal agriculture emissions. Farmed animals’ manure also releases lots of emissions, as nitrous oxide and methane are produced when manure decomposes in anaerobic conditions. This process is especially common when manure is stored in large piles or disposed of in lagoons, which is typical on factory farms where a large amount of animals occupy a small area.

Various other parts of agriculture contribute to greenhouse gas emissions as well. Several agricultural practices affecting soil increase the nitrogen available in it, leading to the release of nitrous oxide. These practices include the drainage of organic soil, certain irrigation practices, and the use of fertilizers, which also contribute to greenhouse gas emissions via their production. Rice cultivation releases methane via the anaerobic digestion of the flooded paddy fields. To prepare for the next growing season, farmers often burn leftover vegetation from their harvest to clear their fields. This crop burning releases carbon dioxide, methane, and nitrous oxide.

Agriculture also contributes to issues surrounding land use, land use change, and forestry. Deforestation to grow crops and raise animals converts the land from a carbon sink to a carbon source because greenhouse gases can no longer be absorbed by the soil and vegetation, and because the gases that were already being stored there have been released. Agriculture is the leading cause of deforestation, releasing about 65 billion tons of carbon dioxide each year through changes in forestry cover alone—driven primarily by the growth of feed products for livestock and grazing land for cattle. Additionally, carbon dioxide is released when cropland and grassland is degraded due to poor soil management techniques.


Similar to the energy sector, most greenhouse gas emissions from the transportation sector result from the combustion of fossil fuels in internal combustion engines. Most transportation requires gasoline or diesel—petroleum-based fuels whose combustion yields large amounts of carbon dioxide and smaller amounts of methane, nitrous oxide, and hydrofluorocarbon, a fluorinated gas. The emissions of the transportation sector can be further broken down into emissions by types of transportation, with road transportation, such as cars and trucks, releasing the most emissions, followed by the aviation industry, the shipping industry, rail transportation, and finally pipelines.

Direct Industry Processes

Just over five percent of total global emissions result from cement and chemicals used in industry. Carbon dioxide is produced in a chemical reaction used to make clinker, a component of cement. It is also produced during the production of ammonia, most of which is then used in synthetic fertilizers. Additionally, nitrous oxide is a byproduct of reactions used to make chemicals such as nitric acid, another component of fertilizers.


Waste products that end up in landfills and other areas were responsible for 1.46 billion tons of methane and 142.38 billion tons of nitrous oxide as of 2018. Decomposition of organic matter accumulated in wastewater systems and in landfills releases methane and nitrous oxide, and treatment of wastewater involving nitrification and denitrification releases additional nitrous oxide.

How Can We Lower Greenhouse Gas Emissions?

While greenhouse gas emissions are still on the rise, lowering greenhouse gas emissions is possible and we know what actions we need to take today to make the biggest impact possible,  on both the individual and institutional levels.

Reducing Dependence on Fossil Fuels Energy

Reducing fossil fuel combustion would directly decrease greenhouse gas emissions from the energy sector, and this can be done several ways. Though the Supreme Court has limited the Environmental Protection Agency’s ability to regulate emissions from power plants, the EPA still has some ability to monitor and manage these emissions with less powerful tools and at scales smaller than those before the decision. Additionally, renewable energy, which does not require fossil fuel combustion, has been expanding and becoming more accessible and efficient. Using solar, geothermal, waste and biomass, wind, or tidal energy, or hydropower is an effective way to decrease dependence on fossil fuels. Increases in energy efficiency and reductions in overall energy use are two other ways to reduce greenhouse gas emissions from the energy sector.

Transitioning Away From Animal Agriculture

Food production is responsible for 25% of all greenhouse gas emissions, so restructuring the global food system is an important opportunity to reduce emissions. Many factory farms have adopted ‘carbon neutral’ commitments in recent years while failing to address that the root of the problem is the current scale and methods of meat production, a classic case of greenwashing. While it is true that practices such as changes to animal feed formulation, smarter handling of farmed animals, changes in field layout, technological monitoring of fertilizer application, and other more efficient agricultural techniques can limit emissions from agriculture, they lead to minor reductions in emissions at best. In order to reduce greenhouse gas emissions enough to reach the goals of the Paris Agreement by 2030, factory farming must be replaced with a sustainable, plant-based food system.

While this may seem like a daunting task, there are steps both individuals and institutions can take to revitalize the global food system and reduce overall meat production. Our own food choices can help combat climate change. Shifting to a plant-based diet can drastically reduce greenhouse gas emissions, as is found in numerous studies including this one performed by scientists at Stanford University and the University of California, Berkeley. In fact, according to a study by Yale University, by switching from the average western diet to a plant-based diet, people can cut their diet-related greenhouse gas emissions in half. Even if some people cannot go fully vegetarian or vegan, adopting a reducetarian diet, one that reduces consumption of animals and animal products without eliminating them completely, is a tangible step we can take in the right direction.

Individuals cannot eradicate factory farming alone, however. Governments can do their part by preventing existing factory farms from expanding, regulating factory farms to ensure they are safer for the climate and our health, eliminating exceptions for factory farms in environmental laws, switching subsidy and incentive programs from supporting meat and dairy to supporting a plant-based food system with less farmed animals overall, and supporting small farmers. Senator Cory Booker (D-NJ) has even introduced the Farm Systems Reform Act, which calls for a ban on factory farming by 2040 and wants to ensure access to affordable and nutritious food for all by reforming our food system. The act includes support for farmers to make this transition, which could also be aided by organizations like Solutions from the Land, as they work to reduce their emissions while continuing to produce and sell goods.

Updating Our Transportation System

We can reduce our emissions from this sector by opting for transportation that either does not require fossil fuels or requires less fossil fuels than traditional modes of transportation. For example, driving an electric car, biking, using an electric scooter, and walking do not require gasoline or diesel. Taking public transportation, carpooling, driving a hybrid car, or using other fuel-saving modes of transportation are effective ways to reduce greenhouse gas emissions if completely eliminating them is not an option.

One important part of making this transition from fossil fuel dependence possible is by having towns and states make changes such as increasing the public transportation budget, adding bike lanes on roads, and expanding sidewalks, and working on other projects to reduce urban sprawl.

Waste Reduction and Diversion

Reducing how much we throw out, especially organic material like food, means less waste in landfills releasing methane. This can be achieved by avoiding overconsumption, composting food, and recycling when possible. Once waste is in landfills, however, incineration with energy recovery can lead to reductions in methane emissions, and have the added benefits of reducing foul smells and space requirements for landfills.

Increasing Carbon Sinks

In addition to reducing the amount of emissions, pulling greenhouse gases out of the atmosphere helps reduce the greenhouse effect. Because carbon sinks absorb more greenhouse gases than they release, they are a vital tool in combating climate change. Forests, grasslands, peatlands, and wetlands are all examples of carbon sinks that must be protected so that their soil, trees, bamboo, and other plants retain all of the carbon they currently store and can absorb more from the atmosphere. For example, the Amazon Rainforest is one of the world’s most important carbon sinks, but in the first half of 2022 experienced the highest deforestation rate in six years—with beef production as the primary culprit Conserving existing carbon sinks against land use change such as deforestation and degradation, and reforesting areas where forests have been destroyed,  is one of the most effective methods of reducing the amount of greenhouse gases in the atmosphere.


Human activity, particularly the dependence on fossil fuels and factory farms, is releasing unprecedented amounts of greenhouse gases into Earth's atmosphere, artificially raising global temperatures. This climate change has negatively impacted both humans and the environment, but reducing our emissions is possible. Taking action on both the individual and institutional levels, sooner rather than later, will give us the best chance to avoid further damage by greenhouse gases.

Julia Collum is an FFAC college advocate studying biology, environmental/ sustainability sciences, and chemistry at the George Washington University in Washington DC.

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