A simple guide to greenhouse gases: Main types and sources

What are GHGs and why do they matter?

Greenhouse gases trap and intensify the sun's heat -- much the way the glass of a greenhouse works -- preventing that heat from escaping into the atmosphere. This phenomenon is called the greenhouse effect. And, as in a greenhouse, some degree of this warming is necessary for life. Without any greenhouse gases whatsoever, the Earth would freeze.

Before the Industrial Revolution around the mid-1700s, natural sources of greenhouse gases did a good job of being in balance. But, since then, greenhouse gases from human activity have thrown this warming out of balance. An ever-increasing amount of the sun's heat -- and the problematic pollution modern activity generates – is trapped in the atmosphere by various GHGs, such as carbon dioxide and methane.

Activities such as driving cars; heating homes; creating building materials, such as cement and steel; raising billions of animals each year for food; manufacturing and disposing of products and food; and even increasingly turning to digitalization and AI are all responsible for greenhouse gas emissions.

All this contributes to global warming -- the heating of the planet due to GHGs -- and climate change -- the long-term shifts in weather patterns. It's true that the planet's weather patterns have had natural shifts throughout history. But, as with greenhouse gases, what concerns scientists and other stakeholders are the forced shifts that come from the things societies do and the immense risks to current and future generations the rapidly heating planet carries.

Due to climate change, weather patterns are already more erratic, with more devastation from hurricanes, wildfires, heating oceans and more, according to a plethora of independent and authoritative scientific groups, such as Climate Central.

The global scientific consensus is definitive that the current climate crisis is not a part of the Earth's natural cycle, but is caused by people, according to the global research review "Greater than 99% consensus on human caused climate change in the peer-reviewed scientific literature," published in Environmental Research Letters on Oct. 19, 2021, which examined a randomized assortment of 3,000 climate science-related papers published since 2012.

In other words, while there are some voices within government and business that are denying that humans have caused and are continuing to cause climate change, the scientific community is virtually unanimous in their agreement that climate change is real, people are causing it, and decisive and major action needs to be taken across all stakeholders.

Already, climate change's worsening impacts are causing more harm to developing countries, according to a 2023 report on climate change from the U.N. Intergovernmental Panel on Climate Change (IPCC).

"Average annual GHG emissions during 2010-2019 were higher than in any previous decade," according to IPCC's "Climate Change 2023 Synthesis Report." "Urgent" action is needed to secure a planet that offers a livable future.

And the hottest year ever shows no signs of slowing.

2024 is on track to be the hottest year on record, according to the World Meteorological Organization.

But there is much business and technology professionals can do to help to address emissions within their companies and improve environmental sustainability.

Understanding more about greenhouse gas emissions is one foundational aspect of this before moving on to reduction efforts, such as climate tech.

Types and sources of greenhouse gases

Greenhouse gases are a broad category within which a number of other heat-trapping gases exist. Here are some of the most concerning.

Carbon dioxide

Carbon dioxide is the top concern when it comes to climate change and global warming. Since the public discourse tends to center on carbon dioxide concepts, here are some other important terms to know:

• CO2. The chemical compound for carbon dioxide -- in other words, its scientific shorthand.
• Carbon. Shortened version of carbon dioxide.
• Carbon emissions. The release of carbon dioxide into the atmosphere.
• Carbon dioxide equivalent, or CO2e. A unit of measure that describes different greenhouse gases in a common unit based on their global warming potential, or GWP.
• Carbon footprint. Total GHGs any entity, such as an individual or organization, generates.
• Carbon pollution. The environmental- and health-harming release of carbon dioxide into the atmosphere, mostly from burning fossil fuels.

The reason carbon dioxide receives so much attention is because it's the main culprit behind the heating planet, although methane is of increasing concern. Since the industrial revolution, CO2 emissions from modern society have been the primary driver of the global temperature rise. Here is some related information:

• By 2019, fossil fuel-related carbon emissions were responsible for the largest growth in gross GHG emissions, according to the IPCC report.
• In the U.S., carbon emissions account for almost 80% of total GHGs, according to the "Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2022."
• Human activities have raised atmospheric CO2 by 50% since the 18th century -- a rise that's greater than the natural increase caused by the last ice age more than 20,000 years ago, according to NASA. Not only is carbon dioxide the most abundant greenhouse gas in the atmosphere, its life span is incredibly long -- lasting in the atmosphere anywhere from 300 to 1,000 years.

Burning oil, using gas and other fossil fuel-related activities are only increasing, resulting in more carbon pollution than ever before. And the reliance on plastics, which are created from fossil fuels and generate massive amounts of waste, is also a major offender in this area, which is what makes alternatives so important, as well as lowering overall consumption, such as through servitization and turning to a circular economy model.

Sources of carbon emissions

A small portion of global CO2 emissions come from natural sources, such as volcanoes and hydrothermal vents, but energy needs, such as heating, account for nearly all global carbon emissions.

Carbon dioxide is created by human activity primarily through the combustion of fossil fuels, like coal, natural gas and oil, which emit CO2 as a byproduct. The major sources of CO2 emissions include the use of these fuels to power transportation, electricity and industry. For example, boilers, furnaces and vehicles burn fossil fuels to generate electricity and heat.

The power and industry sectors account for 60% of total global carbon emissions, while the residential and transport sectors account for about 30%, according to IPCC. Industrial production processes also emit CO2 not related to the combustion of fossil fuels, including petrochemical processes, the production of metals from ores, cement or lime production, the fermentation of biomass and more.

Other sources of carbon emissions include the following:

• Agriculture and domestic livestock.
• Food and beverage production.
• Land use and deforestation.
• The decomposition of organic and inorganic waste.
• Refrigerants and coolants.

The technology sector and IT account for an increasing amount of GHGs generally, as well as carbon specifically. Much of this is due to AI's compute intensity.

Methane

Methane, which is the primary component of natural gas, is the second major source of greenhouse gas emissions and a major driver of climate change, especially in the near term, thanks to its potency.

About 20%-30% of climate warming is due to methane since the Industrial Revolution began in 1750, according to NASA. And, over the last two centuries, atmospheric methane has more than doubled, largely due to human activities.

In contrast to CO2's 300-plus years in the atmosphere, methane's life span ranges from about seven to 12 years in the atmosphere, according to NASA.

However, each molecule is a powerhouse.

Although methane doesn't remain in the atmosphere for as long as carbon, it has more than 80 times the warming potential in the first 20 years it's in the atmosphere, according to the nonprofit Environmental Defense Fund.

That potency, as well as methane's role in the formation of ground-level ozone, makes methane an especially critical aspect of the climate change conversation.

Sources of methane

As with carbon emissions, people are driving an increase in methane emissions via agriculture, fossil fuel production and landfills.

Methane emissions constituted 12% of U.S. human-driven GHGs in 2022, according to the Environmental Protection Agency (EPA).

One overlooked area that people may not realize is the demand for meat as a source of methane.

Raising cattle, swine, sheep, goats and other livestock for food and other products. These animals produce methane -- or CH4 -- as part of their digestion. People breed, raise and slaughter these animals for food and other products, which is why these methane emissions are considered human-driven.

Globally, animal agriculture is a primary source of greenhouse gas emissions and driver of climate change, according to the UN Environment Programme (UNEP). These direct and indirect emissions come from activities such as burning and cutting down forests to make room for livestock grazing areas, pollution to soil and water, and energy-intensive supply chains. Indeed, animal agriculture is responsible for about 14%-20% of global greenhouse gas emissions worldwide and nearly 60% of food-related GHGs, according to UNEP. These are some of the reasons more emphasis on plant-based eating and meat alternatives are growing, since both could cut emissions and help reverse climate change driven by the billons of animals raised each year for food and other products.

In 2019, 18 billion of the 75 billion animals raised for food weren't even eaten, according to "Animal lives embodied in food loss and waste," published in the journal Sustainable Production and Consumption.

Globally, paddy rice production is another area researchers are focused on due to its methane emissions, as well as rice's vulnerability to climate change.

Paddy rice cultivation accounts for about 8% of methane emissions that people create, according to UNEP.

In the U.S., petroleum and natural gas systems are the next largest source of methane emissions after animal agriculture, according to the EPA. CH4 is rising due to oil and gas production, pipelines, refineries, and other energy and industry sources. These account for about 28% of U.S. methane emissions.

Trash is another major source of methane emissions.

Landfills are the third main source of methane emissions in the U.S., according to the EPA, accounting for 16% of total CH4 emissions. Methane is produced as waste breaks down, and it is also a byproduct of wastewater treatment.

Discarded food is another source of waste that produces GHGs, both methane and CO2. Coal mining is another major source.

Nitrous oxide

Nitrous oxide, while not as abundant as carbon dioxide or methane, is still the third-largest GHG contributor to global warming, and this is concerning since it is more potent than carbon and has a longer life span than methane.

For example, about one pound of N2O warms the atmosphere nearly 300 times more than a pound of carbon does over a century, according to "A comprehensive quantification of global nitrous oxide sources and sinks," published in Nature on Oct. 7, 2020. Nitrous oxide emissions from human activities have risen by 30% over the last 40 years, according to "Global nitrous oxide budget (1980-2020)," published in Earth System Data Science. As with carbon and methane emissions, much of this increase is due to increased demand for meat and the burning of fossil fuels, as well as synthetic fertilizers.

In addition, nitrous oxide is now the primary substance responsible for depleting the ozone, according to the Environmental Investigation Agency.

Sources of nitrous oxide

Humans cause about 40% of global nitrous oxide emissions, according to the EPA. The primary source of nitrous oxide comes from synthetic fertilizers for crop production and the manure from livestock -- in particular, cows. Transportation using fossil fuels, food waste and wastewater applications are also major sources.

Fluorinated gases

Fluorinated gases (F-gases) come entirely from human activity. And, although they also tend to be emitted in smaller quantities than other GHGs, they often trap more heat per mass, and they have lengthy life spans.

There are four types of F-gases:

1. Hydrofluorocarbons. HFCs are fluorinated chemicals often used as replacements for ozone-depleting substances, according to the EPA. They can be hundreds to thousands of times more potent than CO2. HFCs can last in the atmosphere up to 270 years.
2. Perfluorocarbons. PFCs are fluorinated hydrocarbon chemicals with strong infrared absorption properties, according to a study published in Atmospheric Chemistry and Physics. Similarly to HFCs, they are highly potent GHGs. PFCs can last anywhere from 2,600 to 50,000 years in the atmosphere, according to the EPA.
3. Sulfur hexafluoride. SF6 is a synthetic fluorinated compound with an extremely stable molecular structure, according to the EPA. It is also the most potent GHG known to date -- over a century, it is 23,500 times more effective at trapping infrared radiation than CO2. SF6 can exist in the atmosphere for upward of 3,200 years.
4. Nitrogen trifluoride. NF3 is a synthetic gas that is colorless and toxic and has a slightly musty odor. It's the second-most potent GHG behind SF6 at more than 17,200 times more potent than CO2, according to Greenhouse Gas Protocol. NF3 can last in the atmosphere for 740 years, according to the EPA.

Due to the high potency and long lifetimes of F-gases, it will likely be a long time before their concentrations decline.

The EU is working to limit F-gases and plans to phase out the use of HFCs by 2050, according to "EU-Rules" from the European Commission.

In the technology realm, this has implications for the data center industry, which uses F-gases to cool servers.

Sources of fluorinated gases

The major sources of fluorinated gases are in refrigeration, cooling and heating.

The refrigeration, air conditioning and heat pump sector is responsible for the largest amount of fluorinated gas emissions, due to refrigerant emissions leakage, according to "The Sixth Carbon Budget: F-gases," published by the Climate Change Committee.

The data center industry uses hydrofluorocarbons to cool servers so they can operate at optimal temperatures. Turning to climate-friendlier cooling methods is part of an overall need to follow green data center design principles.

ChemSec, or the International Chemical Secretariat, an independent nonprofit organization that champions substituting safer alternatives for toxic chemicals, as well as others, are exploring less climate-warming ways of cooling data centers. Some companies are already leading in this effort, such as Volkswagen, which plans to phase out the use of F-gases in its electric car air conditioning by 2030.

Water vapor and ozone

Although water vapor is a greenhouse gas, it dissipates rapidly so is not a concern in and of itself or isn't in natural circumstances. Instead, increased water vapor is a consequence of global warming. And, in a harmful cycle, that's a concern because warmer air holds more water without rain, which then does increase the warm air. That warmer air also amplifies the effects of other GHGs, which is a dangerous feedback loop.

Water vapor also affects the recovery of the ozone layer, according to NASA. Increased water vapor accounts for 40% of ozone loss in the upper stratosphere.

Water vapor and ozone are often considered together in the context of GHGs. Ozone also has dual effects: In the stratosphere, it helps protect Earth from the sun's harmful rays, but at ground level, ozone is a harmful air pollutant, causing smog, which can be dangerous to respiratory health systems, crops and ecosystems. Ground-level ozone also traps heat -- hence its inclusion in GHGs.

Sources of water vapor and ozone

According to the National Snow and Ice Data Center, water vapor comes primarily from the evaporation of water from the planet's oceans, lakes, rivers and vegetation. The water cycle turns water into its gaseous form through evaporation, where it rises into the atmosphere, turns into clouds and precipitates back down to Earth as rain and snow.

The human-driven increase in water vapor comes from the increases in other GHGs, which, in turn, heat the climate, which, in turn, accounts for increases in water vapor -- contributing to the whole cycle worsening.

According to the EPA, ground-level ozone is created by chemical reactions between oxides of nitrogen and volatile organic compounds, which happen when pollutants from cars, power plants, industrial boilers, refineries, chemical plants and more are emitted in the presence of sunlight. Industrial facilities and vehicles are the largest sources of ground-level ozone, but some solvents and cleaning supplies can also emit ozone in smaller quantities.

Business and IT leaders can help lower GHGs

While the news around climate change is worsening, business and IT leaders have an important role to play in creating positive environmental impacts, including lessening their negative impacts.

Not only can IT teams boost sustainability within their department by following green computing principles and measures to boost data center efficiency. They can also support corporate-wide ESG initiatives, as well as sustainability innovations, carbon accounting initiatives, e-waste reduction strategies and communication about sustainability.

Diann Daniel is an executive editor overseeing a number of sites within Informa TechTarget's Enterprise Software and Services group, including Sustainability and ESG.

Jacob Roundy is a freelance writer and editor with more than a decade of experience in a variety of tech topics, such as data centers, business intelligence and sustainability.