Learn About Greenhouse Gas

What Activities Cause Greenhouse Gas Emissions?

Greenhouse gases are those gases that are trapping heat in the atmosphere. We are going to discuss the causes of greenhouse gas emissions and what we can do about them.

1. Carbon Dioxide (CO2)

CO2 enters the air by burning fossil fuels (natural gas, coal, and petroleum), trees, solid waste, and other biological substances, and also because of specific chemical reactions (e.g., production of concrete). Carbon dioxide is eliminated from the air (or”sequestered”) if plants absorb it as a portion of the natural carbon cycle.

Carbon dioxide (CO2) is the original Greenhouse gas emitted through human actions. In 2019, CO2 accounted for roughly 80 percent of all US greenhouse gas emissions from human activities. Carbon dioxide is usually present in the air as part of the planet’s carbon cycle (the natural flow of carbon among the atmosphere, oceans, soil, plants, and animals).

Human activities are changing the carbon cycle–both by adding more CO2 into the air and by changing the ability of natural sinks, such as lands and forests, to remove and store CO2 from the air. While CO2 emissions come from many different natural sources, human-related emissions are responsible for the growth that has occurred in the air since the industrial revolution.

The major human activity that emits CO2 is the combustion of fossil fuels (natural gas, coal, and petroleum ) for power and transport. However, specific industrial processes and land-use changes also emit CO2. The primary sources of CO2 emissions in America are described below.


The combustion of fossil fuels such as petrol and diesel to transport people and products was the biggest source of CO2 emissions in 2019, accounting for approximately 35% of total US CO2 emissions and 28% of total US greenhouse gas emissions. This class includes transportation sources like passenger and highway vehicles, aviation, marine transport, and rail.


Electricity is an important energy source in America and is used to power homes, businesses, and industries. In 2019, the combustion of fossil fuels to create electricity was the second biggest source of CO2 emissions in the country, accounting for approximately 31% of total US CO2 emissions and 24% of total US greenhouse gas emissions. The kinds of fossil fuels used to generate electricity emit various amounts of CO2. To produce a given amount of power, burning coal will produce more CO2 than oil or gas.


Several industrial processes release CO2 through fossil fuel consumption. Several procedures also produce CO2 emissions through chemical reactions that don’t involve combustion, and examples include the production of vitamin products like cement, the generation of metals like iron and steel, and the production of compounds. Fossil fuel combustion from different industrial processes accounted for approximately 16% of total US CO2 emissions and 13% of total US greenhouse gas emissions in 2019. Several industrial processes also use power and so indirectly lead to CO2 emissions from power generation.

Carbon dioxide is continually being exchanged among the ocean, atmosphere, and land surface as it’s both produced and consumed by many microorganisms, plants, and animals. However, the removal and emissions of CO2 by those natural processes tend to balance lost anthropogenic impacts. Since the Industrial Revolution started around 1750, human activities have contributed substantially to climate change with CO2 and other heat-trapping gases into the air.

In the USA, since 1990, the management of forests and other property (e.g., grasslands, cropland, etc.) has acted as a net sink of CO2, meaning that more CO2 is removed from the air and stored in trees and plants than is emitted.

Emissions and Trends

Carbon dioxide emissions from the United States increased by about 3% between 1990 and 2019. Since fossil fuel combustion is the most significant source of greenhouse gas emissions from the US, changes in emissions from fossil fuel combustion have been the leading factor affecting total US emission trends.

Variations in CO2 emissions from fossil fuel combustion are affected by several long-term and short-term variables, such as population growth, economic growth, changing energy costs, new technologies, changing behavior, and seasonal temperatures. Between 1990 and 2019, the growth in CO2 emissions compared with increased energy usage by an expanding economy and population, such as overall growth in emissions from raised demand for travel.

2. Methane (CH4)

Methane is released during the creation and transportation of natural gas, coal, and petroleum. Methane eruptions also occur from livestock and other agricultural practices, land use, and the reduction of organic waste in municipal solid waste landfills.

In 2019, methane (CH4) accounted for roughly 10% of all US greenhouse gas emissions from human activities. Human activities emanating methane include leaks from natural gas systems and the raising of livestock.

Methane is also emitted by natural resources such as natural wetlands. Additionally, natural processes in soil and chemical reactions in the air help remove CH4 in the air. Methane’s life in the atmosphere is significantly less than CO2, but CH4 is significantly more effective at catching radiation than carbon dioxide. Pound for pound, the relative effect of CH4 is 25 times greater than CO2 on 100 years.

Globally, 50-65% of total CH4 emissions come from human actions.2, 3 Methane is emitted from industry, energy, land use, agriculture, and waste management activities, described below.


Domestic livestock such as swine, cattle, sheep, and goats produce CH4 as part of the normal digestive process. Additionally, when animal manure is stored or handled in holding tanks or lagoons, CH4 is generated. As humans raise these animals for food and other goods, the emissions are considered human-related.

When manure and livestock emissions are combined, the Agriculture industry is the biggest source of CH4 emissions from America. While not revealed and less important, emissions of CH4 also happen as a consequence of land management activities and land use in the Land usage, Land-Use Change, and Forestry industry (e.g., grassland fires and forest, decomposition of organic matter in coastal wetlands, etc.).

Energy and Industry

Petroleum and natural gas systems are the second biggest source of CH4 emissions from America. Methane is the main component of natural gas. Methane is emitted into the air during the production, processing, transmission, storage, and distribution of natural gas and the generation, refinement, transit, and storage of crude oil. Coal mining is also a source of CH4 emissions.

Waste From Businesses and Home

Methane is produced in landfills as waste decomposes and in treating wastewater. Landfills are the third-biggest source of CH4 emissions from America. Methane can also be generated from industrial and domestic wastewater treatment and from composting and anaerobic digestion.

3. Nitrous Oxide (N2O)

Nitrous oxide is released during agricultural, land use, industrial activities, solid waste, and combustion of fossil fuels, in addition to during the treatment of wastewater.

Fluorinated gases: Perfluorocarbons, Hydrofluorocarbons, sulfur hexafluoride, and nitrogen trifluoride are artificial, potent greenhouse gases emitted from many different industrial procedures. Fluorinated gases are often used as substitutes for stratospheric ozone-depleting substances (e.g., hydrochlorofluorocarbons, chlorofluorocarbons, and halons).

These gases are generally emitted in smaller amounts, but they are sometimes known as High Global Warming Potential gases (“High GWP gases”) since they are powerful greenhouse gases.

In 2019, nitric oxide (N2O) accounted for approximately 7% of all US greenhouse gas emissions from human activities. Human activities such as fuel combustion, agriculture, wastewater management, and industrial procedures increase the amount of N2O in the air.

Nitrous oxide is also naturally found in the air as part of the Earth’s nitrogen cycle and contains many different natural sources. Nitrous oxide molecules remain in the atmosphere for a mean of 114 years before being eliminated by a sink or destroyed via chemical reactions. The effects of 1 pound of N2O on heating the air are nearly 300 times that of 1 pound of carbon dioxide.1

Globally, about 40% of total N2O emissions come from human activities. Nitrous oxide is produced from agriculture, land use, transport, business, and other actions, described below.


Nitrous Oxide can result from several agricultural soil management actions, such as applying artificial and natural fertilizers and other cropping methods, the management of manure, or the burning of agricultural residuals. Agricultural soil management is the most significant source of N2O emissions in the USA, accounting for approximately 75 percent of total US N2O emissions in 2019.

While not revealed and less critical, emissions of N2O also happen as a consequence of land management activities and land use in the Land Use, Land-Use Change, and Forestry industry (e.g., forest and grassland fires, use of synthetic nitrogen fertilizers into urban lands (e.g., lawns, golf courses) and forest lands, etc.).

Fuel Combustion

Nitrous Oxide is emitted when fuels are burnt. The quantity of N2O emitted from burning fuels is based upon the type of fuel and combustion technology, maintenance, and operating systems.


Nitrous Oxide is produced as a byproduct during the production of compounds like nitric oxide, which can be used to create synthetic commercial fertilizer, and adipic acid production, producing fibers, such as nylon and other synthetic products.


Nitrous Oxide can also be generated from the treatment of domestic wastewater through nitrification and denitrification of the nitrogen present, typically in ammonia, urea, and proteins.

Nitrous oxide emissions arise naturally through many sources linked to the nitrogen cycle, that’s the natural flow of nitrogen among the air, plants, animals, and microorganisms that live in water and soil. Nitrogen takes on several chemical forms throughout the nitrogen cycle, such as N2O.

Natural emissions of N2O are primarily from bacteria breaking down nitrogen in the oceans and soils. Nitrous oxide is removed from the air when absorbed by specific types of bacteria or damaged by chemical reactions or UV radiation.

Emissions and Trends

Nitrous oxide emissions from the US have remained relatively flat between 1990 and 2019. Nitrous oxide emissions from mobile combustion reduced by 60% from 1990 to 2019 because of emission control standards for on-road vehicles. Nitrous oxide emissions from agricultural lands have varied during this period and were about 9% higher in 2019 than in 1990, fundamentally driven by increasing nitrogen fertilizers.

Each gas’s impact on climate change depends on three primary factors:

How Much Is In The Atmosphere?

Concentration, or prosperity, is the amount of a specific gas in the atmosphere. Bigger eruptions of greenhouse gases contribute to high concentrations in the air. Greenhouse gas concentrations are quantified in parts per billion, parts per million, and even parts per trillion. One part per million is equal to a drop of water diluted into approximately 13 gallons of liquid (about the gas tank of a compact car).

How Long Do They Remain In The Atmosphere?

All these gases can remain in the air for different amounts of time, ranging from a couple of years to tens of thousands of years. All these gases stay in the atmosphere long enough to become well mixed, which means that the amount measured in the air is roughly the same worldwide, no matter the origin of the emissions.

How Strongly Do They Affect The Atmosphere?

Some gases are more potent than others at making the world warmer and “hardening the Earth’s blanket.”

Learn About Greenhouse Gas Gases with a higher GWP consume more energy per pound than gases using a lower GWP and contribute to warming Earth.

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