What is greenhouse emissions

Climate Change Indicators: Greenhouse Gases

View Indicators:

Greenhouse gases from human activities are the most significant driver of observed climate change since the mid-20th century. 1 The indicators in this chapter characterize emissions of the major greenhouse gases resulting from human activities, the concentrations of these gases in the atmosphere, and how emissions and concentrations have changed over time. When comparing emissions of different gases, these indicators use a concept called “global warming potential” to convert amounts of other gases into carbon dioxide equivalents.

Why does it matter?

As greenhouse gas emissions from human activities increase, they build up in the atmosphere and warm the climate, leading to many other changes around the world—in the atmosphere, on land, and in the oceans. The indicators in other chapters of this report illustrate many of these changes, which have both positive and negative effects on people, society, and the environment—including plants and animals. Because many of the major greenhouse gases stay in the atmosphere for tens to hundreds of years after being released, their warming effects on the climate persist over a long time and can therefore affect both present and future generations.

Summary of Key Points

Major Long-Lived Greenhouse Gases and Their Characteristics

Greenhouse gas	How it’s produced	Average lifetime in the atmosphere	100-year global warming potential
Carbon dioxide	Emitted primarily through the burning of fossil fuels (oil, natural gas, and coal), solid waste, and trees and wood products. Changes in land use also play a role. Deforestation and soil degradation add carbon dioxide to the atmosphere, while forest regrowth takes it out of the atmosphere.	see below *	1
Methane	Emitted during the production and transport of oil and natural gas as well as coal. Methane emissions also result from livestock and agricultural practices and from the anaerobic decay of organic waste in municipal solid waste landfills.	11.8 years	27.0–29.8 **
Nitrous oxide	Emitted during agricultural and industrial activities, as well as during combustion of fossil fuels and solid waste.	109 years	273
Fluorinated gases	A group of gases that contain fluorine, including hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride, among other chemicals. These gases are emitted from a variety of industrial processes and commercial and household uses and do not occur naturally. Sometimes used as substitutes for ozone-depleting substances such as chlorofluorocarbons.	A few weeks to thousands of years	Varies (the highest is sulfur hexafluoride at 25,200)

This table shows 100-year global warming potentials, which describe the effects that occur over a period of 100 years after a particular mass of a gas is emitted. Global warming potentials and lifetimes come from Tables 7.15 and 7.SM.7 of the Intergovernmental Panel on Climate Change’s Sixth Assessment Report, Working Group I contribution. 3

* Carbon dioxide’s lifetime cannot be represented with a single value because the gas is not destroyed over time, but instead moves among different parts of the ocean–atmosphere–land system. Some of the excess carbon dioxide is absorbed quickly (for example, by the ocean surface), but some will remain in the atmosphere for thousands of years, due in part to the very slow process by which carbon is transferred to ocean sediments.

** Methane’s global warming potential is shown as a range that includes methane from both fossil and non-fossil sources.

See Understanding Global Warming Potentials to learn more about the numbers in the table above and the versions EPA uses for various calculations.

Sources of Data on U.S. Greenhouse Gas Emissions

EPA has two key programs that provide data on greenhouse gas emissions in the United States: the Inventory of U.S. Greenhouse Gas Emissions and Sinks and the Greenhouse Gas Reporting Program. The programs are complementary, providing both a higher-level perspective on the nation’s total emissions and detailed information about the sources and types of emissions from individual facilities. The data in EPA’s U.S. Greenhouse Gas Emissions indicator come from the national inventory.

EPA’s Inventory of Greenhouse Gas Emissions and Sinks

EPA develops an annual report called the Inventory of U.S. Greenhouse Gas Emissions and Sinks (or the GHG Inventory). This report tracks trends in total annual U.S. emissions by source (or sink), economic sector, and greenhouse gas going back to 1990. EPA uses national energy data, data on national agricultural activities, and other national statistics to provide a comprehensive accounting of total greenhouse gas emissions for all man-made sources in the United States. This inventory fulfills the nation’s obligation to provide an annual emissions report under the United Nations Framework Convention on Climate Change.

EPA’s Greenhouse Gas Reporting Program

Since 2010, EPA’s Greenhouse Gas Reporting Program has been collecting annual emissions data from industrial sources that directly emit large amounts of greenhouse gases. Generally, facilities that emit more than 25,000 metric tons of carbon dioxide equivalents per year are required to report. The program also collects data from entities known as «suppliers» that supply certain fossil fuels and industrial gases that will emit greenhouse gases into the atmosphere if burned or released—for example, refineries that supply petroleum products such as gasoline. The Greenhouse Gas Reporting Program only requires reporting; it is not an emissions control program. This program helps EPA and the public understand where greenhouse gas emissions are coming from, and will improve our ability to make informed policy, business, and regulatory decisions.

Learn more about the Greenhouse Gas Reporting Program and explore data by facility, industry, location, or gas using a data visualization and mapping tool called FLIGHT. You can also review state- or tribal-specific emissions using interactive fact sheets and download detailed data via EPA’s Envirofacts database.

Overview of Greenhouse Gases

On this page:

Total U.S. Emissions in 2020 = 5,981 Million Metric Tons of CO2 equivalent (excludes land sector). Percentages may not add up to 100% due to independent rounding.

Gases that trap heat in the atmosphere are called greenhouse gases. This section provides information on emissions and removals of the main greenhouse gases to and from the atmosphere. For more information on the other climate forcers, such as black carbon, please visit the Climate Change Indicators: Climate Forcing page.

Fluorinated gases : Hydrofluorocarbons, perfluorocarbons, sulfur hexafluoride, and nitrogen trifluoride are synthetic, powerful greenhouse gases that are emitted from a variety of household, commercial, and industrial applications and processes. Fluorinated gases (especially hydrofluorocarbons) are sometimes used as substitutes for stratospheric ozone-depleting substances (e.g., chlorofluorocarbons, hydrochlorofluorocarbons, and halons). Fluorinated gases are typically emitted in smaller quantities than other greenhouse gases, but they are potent greenhouse gases. With global warming potentials (GWPs) that typically range from thousands to tens of thousands, they are sometimes referred to as high-GWP gases because, for a given amount of mass, they trap substantially more heat than CO₂.

Each gas’s effect on climate change depends on three main factors:

How much is in the atmosphere?

Concentration, or abundance, is the amount of a particular gas in the air. Larger emissions of greenhouse gases lead to higher concentrations in the atmosphere. Greenhouse gas concentrations are measured in parts per million, parts per billion, and even parts per trillion. One part per million is equivalent to one drop of water diluted into about 13 gallons of liquid (roughly the fuel tank of a compact car). To learn more about the increasing concentrations of greenhouse gases in the atmosphere, visit the Climate Change Indicators: Atmospheric Concentrations of Greenhouse Gases page.

How long do they stay in the atmosphere?

Each of these gases can remain in the atmosphere for different amounts of time, ranging from a few years to thousands of years. All of these gases remain in the atmosphere long enough to become well mixed, meaning that the amount that is measured in the atmosphere is roughly the same all over the world, regardless of the source of the emissions.

How strongly do they impact the atmosphere?

Some gases are more effective than others at making the planet warmer and «thickening the Earth’s blanket.»

For each greenhouse gas, a Global Warming Potential (GWP) was developed to allow comparisons of the global warming impacts of different gases. Specifically, it is a measure of how much energy the emissions of 1 ton of a gas will absorb over a given period of time, relative to the emissions of 1 ton of carbon dioxide (CO₂). Gases with a higher GWP absorb more energy, per pound emitted, than gases with a lower GWP, and thus contribute more to warming Earth.

Carbon Dioxide Emissions

Chemical Formula: CO₂
Lifetime in Atmosphere: See below 1
Global Warming Potential (100-year): 1

Carbon dioxide (CO₂) is the primary greenhouse gas emitted through human activities. In 2020, CO₂ accounted for about 79% of all U.S. greenhouse gas emissions from human activities. Carbon dioxide is naturally present in the atmosphere as part of the Earth’s carbon cycle (the natural circulation of carbon among the atmosphere, oceans, soil, plants, and animals). Human activities are altering the carbon cycle–both by adding more CO₂ to the atmosphere and by influencing the ability of natural sinks, like forests and soils, to remove and store CO₂ from the atmosphere. While CO₂ emissions come from a variety of natural sources, human-related emissions are responsible for the increase that has occurred in the atmosphere since the industrial revolution. 2

The main human activity that emits CO₂ is the combustion of fossil fuels (coal, natural gas, and oil) for energy and transportation. Certain industrial processes and land-use changes also emit CO₂. The main sources of CO₂ emissions in the United States are described below.

Carbon dioxide is constantly being exchanged among the atmosphere, ocean, and land surface as it is both produced and absorbed by many microorganisms, plants, and animals. Emissions and removal of CO₂ by these natural processes, however, tend to balance, absent anthropogenic impacts. Since the Industrial Revolution began around 1750, human activities have contributed substantially to climate change by adding CO₂ and other heat-trapping gases to the atmosphere.

In the United States, the management of forests and other land (e.g., cropland, grasslands, etc.) has acted as a net sink of CO₂, which means that more CO₂ is removed from the atmosphere, and stored in plants and trees, than is emitted. This carbon sink offset is about 14% of total emissions in 2020 and is discussed in more detail in the Land Use, Land-Use Change, and Forestry section.

To find out more about the role of CO₂ in warming the atmosphere and its sources, visit the Climate Change Indicators page.

Emissions and Trends

Carbon dioxide emissions in the United States decreased by about 8% between 1990 and 2020. Since the combustion of fossil fuel is the largest source of greenhouse gas emissions in the United States, changes in emissions from fossil fuel combustion have historically been the dominant factor affecting total U.S. emission trends. Changes in CO₂ emissions from fossil fuel combustion are influenced by many long-term and short-term factors, including population growth, economic growth, changing energy prices, new technologies, changing behavior, and seasonal temperatures. In 2020, the decrease in CO₂ emissions from fossil fuel combustion corresponded with a decrease in energy use as a result of decreases in economic, manufacturing, and travel activity in response to the coronavirus pandemic, in addition to a continued shift from coal to less carbon-intensive natural gas and renewables in the electric power sector.

Reducing Carbon Dioxide Emissions

The most effective way to reduce CO₂ emissions is to reduce fossil fuel consumption. Many strategies for reducing CO₂ emissions from energy are cross-cutting and apply to homes, businesses, industry, and transportation.

EPA is taking common sense regulatory actions to reduce greenhouse gas emissions.

Improving the insulation of buildings, traveling in more fuel-efficient vehicles, and using more efficient electrical appliances are all ways to reduce energy use, and thus CO₂ emissions.

Reducing personal energy use by turning off lights and electronics when not in use reduces electricity demand. Reducing distance traveled in vehicles reduces petroleum consumption. Both are ways to reduce energy CO₂ emissions through conservation.

Learn more about What You Can Do at Home, at School, in the Office, and on the Road to save energy and reduce your carbon footprint.

Producing more energy from renewable sources and using fuels with lower carbon contents are ways to reduce carbon emissions.

Carbon Capture and Sequestration (CCS)

Carbon dioxide capture and sequestration is a set of technologies that can potentially greatly reduce CO₂ emissions from new and existing coal- and gas-fired power plants, industrial processes, and other stationary sources of CO₂. For example, a CCS project might capture CO₂ from the stacks of a coal-fired power plant before it enters the atmosphere, transport the CO₂ via pipeline, and inject the CO₂ deep underground at a carefully selected and suitable subsurface geologic formation, such as a nearby abandoned oil field, where it is securely stored.

Changes in Uses of Land and Land Management Practices

1 Atmospheric CO₂ is part of the global carbon cycle, and therefore its fate is a complex function of geochemical and biological processes. Some of the excess carbon dioxide will be absorbed quickly (for example, by the ocean surface), but some will remain in the atmosphere for thousands of years, due in part to the very slow process by which carbon is transferred to ocean sediments.

2 IPCC (2013). Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. [Stocker, T. F., D. Qin, G.-K. Plattner, M. Tignor, S. K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P. M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1585 pp.

Methane Emissions

Chemical Formula: CH₄
Lifetime in Atmosphere: 12 years
Global Warming Potential (100-year): 25 1

In 2020, methane (CH₄) accounted for about 11% of all U.S. greenhouse gas emissions from human activities. Human activities emitting methane include leaks from natural gas systems and the raising of livestock. Methane is also emitted by natural sources such as natural wetlands. In addition, natural processes in soil and chemical reactions in the atmosphere help remove CH₄ from the atmosphere. Methane’s lifetime in the atmosphere is much shorter than carbon dioxide (CO₂), but CH₄ is more efficient at trapping radiation than CO₂. Pound for pound, the comparative impact of CH₄ is 25 times greater than CO₂ over a 100-year period. 1

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

Methane is also emitted from a number of natural sources. Natural wetlands are the largest source, emitting CH₄ from bacteria that decompose organic materials in the absence of oxygen. Smaller sources include termites, oceans, sediments, volcanoes, and wildfires.

To find out more about the role of CH₄ in warming the atmosphere and its sources, visit the Climate Change Indicators page.

Emissions and Trends

Methane emissions in the United States decreased by 17% between 1990 and 2020. During this time period, emissions increased from sources associated with agricultural activities, while emissions decreased from other sources including landfills and coal mining and from natural gas and petroleum systems.

Note: All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2020. These estimates use a global warming potential for methane of 25, based on reporting requirements under the United Nations Framework Convention on Climate Change.

Reducing Methane Emissions

There are a number of ways to reduce CH₄ emissions. Some examples are discussed below. EPA has a series of voluntary programs for reducing CH₄ emissions, in addition to regulatory initiatives. EPA also supports the Global Methane Initiative, an international partnership encouraging global methane reduction strategies.

Examples of Reduction Opportunities for Methane

Upgrading the equipment used to produce, store, and transport oil and natural gas can reduce many of the leaks that contribute to CH₄ emissions. Methane from coal mines can also be captured and used for energy. Learn more about the EPA’s Natural Gas STAR Program and Coalbed Methane Outreach Program.

Methane from manure management practices can be reduced and captured by altering manure management strategies. Additionally, modifications to animal feeding practices may reduce emissions from enteric fermentation. Learn more about improved manure management practices at EPA’s AgSTAR Program.

Because CH₄ emissions from landfill gas are a major source of CH₄ emissions in the United States, emission controls that capture landfill CH₄ are an effective reduction strategy. Learn more about these opportunities and the EPA’s Landfill Methane Outreach Program.

References

1 IPCC (2007). Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. [S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press. Cambridge, United Kingdom 996 pp.
2 IPCC (2013). Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. [Stocker, T. F., D. Qin, G.-K. Plattner, M. Tignor, S. K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P. M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1585 pp.
3 Saunois et al. (2020). The Global Methane Budget 2000-2017. Earth Syst. Sci. Data, 12, 1561–1623, 2020. https://doi.org/10.5194/essd-12-1561-2020.

Nitrous Oxide Emissions

Chemical Formula: N₂O
Lifetime in Atmosphere: 114 years
Global Warming Potential (100-year): 298 1

In 2020, nitrous oxide (N₂O) accounted for about 7% of all U.S. greenhouse gas emissions from human activities. Human activities such as agriculture, fuel combustion, wastewater management, and industrial processes are increasing the amount of N₂O in the atmosphere. Nitrous oxide is also naturally present in the atmosphere as part of the Earth’s nitrogen cycle and has a variety of natural sources. Nitrous oxide molecules stay in the atmosphere for an average of 114 years before being removed by a sink or destroyed through chemical reactions. The impact of 1 pound of N₂O on warming the atmosphere is almost 300 times that of 1 pound of carbon dioxide. 1

Globally, about 40% of total N₂O emissions come from human activities. 2 Nitrous oxide is emitted from agriculture, land use, transportation, industry, and other activities, described below.

Nitrous oxide emissions occur naturally through many sources associated with the nitrogen cycle, which is the natural circulation of nitrogen among the atmosphere, plants, animals, and microorganisms that live in soil and water. Nitrogen takes on a variety of chemical forms throughout the nitrogen cycle, including N₂O. Natural emissions of N₂O are mainly from bacteria breaking down nitrogen in soils and the oceans. Nitrous oxide is removed from the atmosphere when it is absorbed by certain types of bacteria or destroyed by ultraviolet radiation or chemical reactions.

To find out more about the sources of N₂O and its role in warming the atmosphere, visit the Climate Change Indicators page.

Emissions and Trends

Nitrous oxide emissions in the United States decreased by 5% between 1990 and 2020. During this time, nitrous oxide emissions from mobile combustion decreased by 61% as a result of emission control standards for on-road vehicles. Nitrous oxide emissions from agricultural soils have varied during this period and were about the same in 2020 as in 1990.

Reducing Nitrous Oxide Emissions

There are a number of ways to reduce emissions of N₂O, discussed below.

Emissions Source	How Emissions Can be Reduced
Industry

Examples of Reduction Opportunities for Nitrous Oxide Emissions

The application of nitrogen fertilizers accounts for the majority of N₂O emissions in the United States. Emissions can be reduced by reducing nitrogen-based fertilizer applications and applying these fertilizers more efficiently, 3 as well as modifying a farm’s manure management practices.

References

1 IPCC (2007) Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. [S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press. Cambridge, United Kingdom 996 pp.
2 IPCC (2013). Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. [Stocker, T. F., D. Qin, G.-K. Plattner, M. Tignor, S. K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P. M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1585 pp.
3 EPA (2005). Greenhouse Gas Mitigation Potential in U.S. Forestry and Agriculture. U.S. Environmental Protection Agency, Washington, DC, USA.

Emissions of Fluorinated Gases

Chemical Formulas:
HFCs, PFCs, NF₃, SF₆
Lifetime in Atmosphere:
HFCs: up to 270 years
PFCs: 2,600–50,000 years
NF₃: 740 years
SF₆: 3,200 years
Global Warming Potential (100-year): 1
HFCs: up to 14,800
PFCs: up to 12,200
NF₃: 17,200
SF₆: 22,800

Unlike many other greenhouse gases, fluorinated gases have no significant natural sources and come almost entirely from human-related activities. They are emitted through their use as substitutes for ozone-depleting substances (e.g., as refrigerants) and through a variety of industrial processes such as aluminum and semiconductor manufacturing. Many fluorinated gases have very high global warming potentials (GWPs) relative to other greenhouse gases, so small atmospheric concentrations can have disproportionately large effects on global temperatures. They can also have long atmospheric lifetimes—in some cases, lasting thousands of years. Like other long-lived greenhouse gases, most fluorinated gases are well-mixed in the atmosphere, spreading around the world after they are emitted. Many fluorinated gases are removed from the atmosphere only when they are destroyed by sunlight in the far upper atmosphere. In general, fluorinated gases are the most potent and longest lasting type of greenhouse gases emitted by human activities.

There are four main categories of fluorinated gases—hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF₆), and nitrogen trifluoride (NF₃). The largest sources of fluorinated gas emissions are described below.

To find out more about the role of fluorinated gases in warming the atmosphere and their sources, visit the Fluorinated Greenhouse Gas Emissions page.

Emissions and Trends

Overall, fluorinated gas emissions in the United States have increased by about 90% between 1990 and 2020. This increase has been driven by a 284% increase in emissions of hydrofluorocarbons (HFCs) since 1990, as they have been widely used as a substitute for ozone-depleting substances. Emissions of perfluorocarbons (PFCs) and sulfur hexafluoride (SF₆) have actually declined during this time due to emission-reduction efforts in the aluminum production industry (PFCs) and the electrical transmission and distribution industry (SF₆).

Reducing Fluorinated Gas Emissions

Because most fluorinated gases have a very long atmospheric lifetime, it will take many years to see a noticeable decline in current concentrations. There are, however, a number of ways to reduce emissions of fluorinated gases, described below.

Emissions Source	Examples of How Emissions Can be Reduced
Agriculture

Examples of Reduction Opportunities for Fluorinated Gases

Refrigerants used by businesses and residences emit fluorinated gases. Emissions can be reduced by better handling of these gases and use of substitutes with lower global warming potentials and other technological improvements. Visit EPA’s Ozone Layer Protection site and HFC Phasedown site to learn more about reduction opportunities in this sector.

Industrial users of fluorinated gases can reduce emissions by adopting fluorinated gas recycling and destruction processes, optimizing production to minimize emissions, and replacing these gases with alternatives. EPA has experience with these gases in the following sectors:

Sulfur hexafluoride is an extremely potent greenhouse gas that is used for several purposes when transmitting electricity through the power grid. EPA is working with industry to reduce emissions through the SF₆ Emission Reduction Partnership for Electric Power Systems, which promotes leak detection and repair, use of recycling equipment, and consideration of alternative technologies that do not use SF₆.

Hydrofluorocarbons (HFCs) are released through the leakage of refrigerants used in vehicle air-conditioning systems. Leakage can be reduced through better system components and through the use of alternative refrigerants with lower global warming potentials than those presently used. EPA’s light-duty and heavy-duty vehicle standards provided incentives for manufacturers to produce vehicles with lower HFC emissions.

References

1 IPCC (2007) Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. [S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press. Cambridge, United Kingdom 996 pp.

5,981 million metric tons of CO₂: What does that mean?

An explanation of units:

A million metric tons is equal to about 2.2 billion pounds, or 1 trillion grams. For comparison, a small car is likely to weigh a little more than 1 metric ton. Thus, a million metric tons is roughly the same mass as 1 million small cars!

The U.S. Inventory uses metric units for consistency and comparability with other countries. For reference, a metric ton is a little bit larger (about 10%) than a U.S. «short» ton.

GHG emissions are often measured in carbon dioxide (CO₂) equivalent. To convert emissions of a gas into CO₂ equivalent, its emissions are multiplied by the gas’s Global Warming Potential (GWP). The GWP takes into account the fact that many gases are more effective at warming Earth than CO₂, per unit mass.

Carbon dioxide levels are at a record high. Here’s what you need to know.

Carbon dioxide, a key greenhouse gas that drives global climate change, continues to rise every month. Find out the dangerous role it and other gases play.

By trapping heat from the sun, greenhouse gases have kept Earth’s climate habitable for humans and millions of other species. But those gases are now out of balance and threaten to change drastically which living things can survive on this planet—and where.

Atmospheric levels of carbon dioxide—the most dangerous and prevalent greenhouse gas—are at the highest levels ever recorded. Greenhouse gas levels are so high primarily because humans have released them into the air by burning fossil fuels. The gases absorb solar energy and keep heat close to Earth’s surface, rather than letting it escape into space. That trapping of heat is known as the greenhouse effect.

The roots of the greenhouse effect concept lie in the 19th century, when French mathematician Joseph Fourier calculated in 1824 that the Earth would be much colder if it had no atmosphere. In 1896, Swedish scientist Svante Arrhenius was the first to link a rise in carbon dioxide gas from burning fossil fuels with a warming effect. Nearly a century later, American climate scientist James E. Hansen testified to Congress that “The greenhouse effect has been detected and is changing our climate now.»

Today, climate change is the term scientists use to describe the complex shifts, driven by greenhouse gas concentrations, that are now affecting our planet’s weather and climate systems. Climate change encompasses not only the rising average temperatures we refer to as global warming but also extreme weather events, shifting wildlife populations and and habitats, rising seas, and a range of other impacts.

Climate 101: Causes and Effects

Governments and organizations around the world such as the Intergovernmental Panel on Climate Change (IPCC), the United Nations body that tracks the latest climate change science, are measuring greenhouse gases, tracking their impacts, and implementing solutions.

Major greenhouse gases and sources

Carbon dioxide (CO₂): Carbon dioxide is the primary greenhouse gas, responsible for about three-quarters of emissions. It can linger in the atmosphere for thousands of years. In 2018, carbon dioxide levels reached 411 parts per million at Hawaii’s Mauna Loa Atmospheric Baseline Observatory, the highest monthly average ever recorded. Carbon dioxide emissions mainly come from burning organic materials: coal, oil, gas, wood, and solid waste.

Methane (CH₄): The main component of natural gas, methane is released from landfills, natural gas and petroleum industries, and agriculture (especially from the digestive systems of grazing animals). A molecule of methane doesn’t stay in the atmosphere as long as a molecule of carbon dioxide—about 12 years—but it is at least 84 times more potent over two decades. It accounts for about 16 percent of all greenhouse gas emissions.

Nitrous Oxide (N₂O): Nitrous oxide occupies a relatively small share of global greenhouse gas emissions—about six percent—but it is 264 times more powerful than carbon dioxide over 20 years, and its lifetime in the atmosphere exceeds a century, according to the IPCC. Agriculture and livestock, including fertilizer, manure, and burning of agricultural residues, along with burning fuel, are the biggest sources of nitrous oxide emissions.

Industrial gases: Fluorinated gases such as hydrofluorocarbons, perfluorocarbons, chlorofluorocarbons, sulfur hexafluoride (SF₆), and nitrogen trifluoride (NF₃) have heat-trapping potential thousands of times greater than CO₂ and stay in the atmosphere for hundreds to thousands of years. Accounting for about 2 percent of all emissions, they’re used as refrigerants, solvents, and in manufacturing, sometimes occurring as byproducts.

Other greenhouse gases include water vapor and ozone (O₃). Water vapor is actually the world’s most abundant greenhouse gas, but it is not tracked the same way as other greenhouse gases because it is not directly emitted by human activity and its effects are not well understood. Similarly, ground-level or tropospheric ozone (not to be confused with the protective stratospheric ozone layer higher up) is not emitted directly but emerges from complex reactions among pollutants in the air.

Effects of greenhouse gases

Greenhouse gases have far-ranging environmental and health effects. They cause climate change by trapping heat, and they also contribute to respiratory disease from smog and air pollution. Extreme weather, food supply disruptions, and increased wildfires are other effects of climate change caused by greenhouse gases. The typical weather patterns we’ve grown to expect will change; some species will disappear; others will migrate or grow. (Read more about greenhouse gas effects via climate change here.)

Greehouse gases: What are they? What can we do to reduce emissions?

Greenhouse gases are gases in the atmosphere that retain the heat emitted by the earth’s surface, atmosphere, and clouds. These gases can have a natural or anthropogenic origin and their properties cause a phenomenon known as the greenhouse effect.

What is the greenhouse effect?

Rising temperatures lead to melting glaciers, water heating (especially ocean water) and changing seasons. As regards the climate, it causes an increase in rainfall and an increase in the surface of dry areas.

Which are the greenhouse gases?

Water vapor (H2O), carbon dioxide (CO2), nitrous oxide (N2O), methane (CH4) and sulfur hexafluoride (SF6) are the main greenhouse gases in the Earth’s atmosphere. In addition to these gases of both natural and anthropic origin, there are other greenhouse gases released into the atmosphere. Produced exclusively by man, there are the halocarbons, among which are chlorofluorocarbons (CFCs).

Water vapor

Water vapor is the greenhouse gas with the highest concentration. For this reason, it causes about 2/3 of the greenhouse effect, trapping the infrared radiation within its molecules.

Carbon dioxide

Carbon dioxide produces about 15% of the greenhouse effect and interacts with the atmosphere for both natural and anthropic causes. Without the intervention of man, the amount of CO2 finds its balance in every ecosystem. In this case, we can observe slight variations of seasonal concentration due to the photosynthesis of plants. On the other hand, anthropological emissions of carbon dioxide are caused by the combustion of coal, oil and natural gas, deforestation and intensive use of agricultural land.

Methane

Methane, on the other hand, produces 10% of the greenhouse effect and is caused by 60-80% by man. Its ability to hold heat is about 20 times greater than carbon dioxide’s one. This gas is produced by the degradation of organic material in an oxygen-free environment. The main sources of methane on Earth are landfills, swamps, fossil fuel extraction sites, livestock digestion, and rice fields.

Nitrous oxide

Nitrous oxide represents only a very small part of the atmosphere, but it’s almost 300 times more powerful than CO2 in retaining heat. Most of this molecule is the result of microbiological processes, such as nitrification and denitrification in the subsoil.

Halocarbons

Halocarbons, just like methane, represent a very small part of the atmosphere. However, the heating potential is from 3000 to 13 thousand times higher than carbon dioxide. This makes them a very powerful greenhouse gas that derives exclusively from the action of man. Until the ‘70s, people used CFCs as propellants in spray cans, solvents, and some adhesives. With the Montreal Protocol, there was a big change, as it harmed the atmospheric ozone layer. Unfortunately, these gases stay in the air for up to 400 years, so it will take some time before they are no longer present in the air.

Ozone

Ozone naturally forms part of the stratosphere, at a height of 45 km, thank to the reaction between three oxygen and UV rays. In this layer of the atmosphere, it works as a solar filter. At lower altitudes instead, it is considered a slightly polluting greenhouse gas. Ozone causes acid rain and some respiratory diseases.

Which countries emit more greenhouse gases in the world?

In 2015, experts calculated total world CO2 emissions in kilotonnes and consequently drew up a list of the most polluting countries.

The top 5 countries are:

followed by Japan, Brasil, Indonesia, Iran, and Canada.

Which countries emit more greenhouse gases in Europe?

In 2017, they drew up a ranking of the most polluting nations in Europe.

The top 10 countries are:

How can we reduce greenhouse gas emissions?

Nowadays, it’s important to develop strategies to reduce greenhouse gas emissions and also to contribute to the fight against global warming and climate change.

We have to do something for the future of our planet. Besides, it’s essential to ask governments to implement effective environmental policies.

10 good actions to undertake in everyday life to reduce greenhouse gas

My name is Alessia, I’m 21 years old and I’m studying modern languages for touristic and business mediation. I’m a down-to-earth, straightforward and sincere girl. I love animals and nature. A long walk in the open air is all I want after a week of crazy study!
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Greenhouse gases: Causes, sources and environmental effects

Greenhouse gases help keep the Earth at a habitable temperature — until there is too much of them.

Behind the phenomena of global warming and climate change lies the increase in greenhouse gases in our atmosphere. A greenhouse gas is any gaseous compound in the atmosphere that is capable of absorbing infrared radiation, thereby trapping and holding heat in the atmosphere. By increasing the heat in the atmosphere, greenhouse gases are responsible for the greenhouse effect, which ultimately leads to global warming. (The effects of global warming can been seen across the globe.)

Solar radiation and the «greenhouse effect»

Global warming isn’t a recent scientific concept. The basics of the phenomenon were worked out well over a century ago by Swedish physicist and chemist Svante Arrhenius, in 1896. His paper, published in the Philosophical Magazine and Journal of Science, was the first to quantify the contribution of carbon dioxide to what scientists now call the «greenhouse effect.»

The greenhouse effect occurs because the sun bombards Earth with enormous amounts of radiation that strike Earth’s atmosphere in the form of visible light, plus ultraviolet (UV), infrared (IR) and other types of radiation that are invisible to the human eye. UV radiation has a shorter wavelength and a higher energy level than visible light, while IR radiation has a longer wavelength and a weaker energy level. About 30% of the radiation that strikes Earth is reflected back out to space by clouds, ice and other reflective surfaces. The remaining 70% is absorbed by the oceans, the land and the atmosphere, according to NASA’s Earth Observatory.

As they heat up, the oceans, land and atmosphere release heat in the form of IR thermal radiation, which passes out of the atmosphere and into space. It’s this equilibrium of incoming and outgoing radiation that makes the Earth habitable, with an average temperature of about 59 degrees Fahrenheit (15 degrees Celsius), according to NASA. Without this atmospheric equilibrium, Earth would be as cold and lifeless as its moon, or as blazing hot as Venus. The moon, which has almost no atmosphere, is about minus 243 F (minus 153 C) on its dark side. Venus, on the other hand, has a very dense atmosphere that traps solar radiation; the average temperature on Venus is about 864 F (462 C).

The exchange of incoming and outgoing radiation that warms the Earth is often referred to as the greenhouse effect because an agricultural greenhouse works in much the same way. Incoming shortwave UV radiation easily passes through the glass walls of a greenhouse and is absorbed by the plants and hard surfaces inside. Weaker, longwave IR radiation, however, has difficulty passing through the glass walls and is thereby trapped inside, warming the greenhouse.

How greenhouse gases cause global warming

The gases in the atmosphere that absorb radiation are known as «greenhouse gases» (abbreviated as GHG) because they are largely responsible for the greenhouse effect. The greenhouse effect, in turn, is one of the leading causes of global warming. The most significant greenhouse gases, according to the Environmental Protection Agency (EPA), are: water vapor (H2O), carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O).

«While oxygen (O2) is the second most abundant gas in our atmosphere, O2 does not absorb thermal infrared radiation,» Michael Daley, an associate professor of environmental science at Lasell College in Massachusetts, told Live Science.

Global warming and the greenhouse gases that cause it occur naturally — without them, Earth’s average surface temperature would be a gelid zero degrees F (minus 18 C). But the amount of greenhouse gases in the atmosphere has skyrocketed to detrimental levels in recent history.

During the 20,000-year period before the Industrial Revolution, atmospheric CO2 fluctuated between about 180 parts per million (ppm) during ice ages and 280 ppm during interglacial warm periods. However, since the beginning of the Industrial Revolution in the 1750s, the amount of CO2 has risen nearly 50%, according to NASA’s Global Climate Change portal. Today, CO2 levels stand at over 410 ppm.

Fluorinated gases — gases to which the element fluorine has been added — are created during industrial processes and are also considered greenhouse gases. These include hydrofluorocarbons, perfluorocarbons and sulfur hexafluoride. Although they are present in the atmosphere in very small concentrations, they trap heat very effectively, making them high «global warming potential» (GWP) gases.

Chlorofluorocarbons (CFCs), once used as refrigerants and aerosol propellants until they were phased out by international agreement, are also greenhouse gases.

There are three factors that affect the degree to which a greenhouse gas will influence global warming: Its abundance in the atmosphere, how long it stays in the atmosphere and its GWP. For example, water vapor is the most abundant greenhouse gas, but carbon dioxide has a more significant impact on global warming due to its abundance in the atmosphere plus its relatively long atmospheric lifetime of 300 to 1,000 years, according to NASA. Water vapor, on the other hand, has an atmospheric lifetime of no more than 10 days, according to a 2020 study published in the Journal of the Atmospheric Sciences.

Methane is about 21 times more efficient at absorbing radiation than CO2, giving it a higher GWP rating, even though it stays in the atmosphere for only about 12 years, according to the United Nations Framework Convention on Climate Change (UNFCCC). Although methane and other GHGs are capable of trapping more heat than CO2, scientists still consider carbon dioxide to be the dominant greenhouse gas because its warming effect outlives the others’ effects by centuries.

Sources of greenhouse gases

Some greenhouse gases, such as methane, are produced through agricultural practices, in the form of livestock manure, for example. Others, like CO2, largely result from natural processes like respiration, and from the burning of fossil fuels like coal, oil and gas.

Another primary source of CO2 is deforestation. When trees are felled to produce goods or heat, they release the carbon that is normally stored for photosynthesis. This process releases up to 4.8 billion metric tons of carbon into the atmosphere every year, according to the World Resources Institute.

Forestry and other land-use practices can offset some of these greenhouse gas emissions. «Replanting helps to reduce the buildup of carbon dioxide in the atmosphere as growing trees sequester carbon dioxide through photosynthesis,» Daley told Live Science. «However, forests cannot sequester all of the carbon dioxide we are emitting to the atmosphere through the burning of fossil fuels, and a reduction in fossil fuel emissions is still necessary to avoid buildup in the atmosphere.»

Worldwide, the output of greenhouse gases is a source of grave concern. According to NOAA’s Climate.gov, over the past 60 years, atmospheric CO2 has increased at an annual rate that’s 100 times faster than previous natural increases. The last time global atmospheric CO2 amounts were this high was 3 million years ago, when temperatures were up to 5.4 degrees F (3 degrees C) higher than during the pre-industrial era. As a result of modern-day CO2-induced global warming, 2016 was the warmest year on record, with 2019 and 2020 ranking as the next warmest, respectively. In fact, the six hottest years on record have all occurred since 2015, according to the World Meteorological Organization.

«The warming we observe affects atmospheric circulation, which impacts rainfall patterns globally,» said Josef Werne, an associate professor in the Department of Geology and Planetary Science at the University of Pittsburgh. «This will lead to big environmental changes, and challenges, for people all across the globe.»

Our planet’s future

If current trends continue, scientists, government officials and a growing number of citizens fear that the worst effects of global warming — extreme weather, rising sea levels, plant and animal extinctions, ocean acidification, major shifts in climate and unprecedented social upheaval — will be inevitable.

In an effort to combat GHG-induced global warming, the U.S. government created a climate action plan in 2013. And in April 2016, representatives from 73 countries signed the Paris Agreement, an international pact to combat climate change by investing in a sustainable, low-carbon future, according to the UNFCCC. Although the U.S. withdrew from the Paris Agreement in 2017, it rejoined in late-January 2021. President Biden’s administration has also set a target of reducing U.S. emissions by 50-52% of 2005 levels by the year 2030. (Emissions are routinely compared to those in 2005 — the year U.S. emissions of CO2 peaked at nearly 6 billion tons.)

In order to limit global warming to the 2.7 degree F (1.5 degree C) target set by the Paris Agreement, the world still needs to cut its CO2 emissions by 7.6% for the next decade, according to the UN Environment Programme.

Researchers around the world continue to work toward finding ways to lower greenhouse gas emissions and mitigate their effects. One potential solution scientists are examining is to suck some of the carbon dioxide out of the atmosphere and bury it underground indefinitely. Advocates argue that carbon capture and storage is technologically feasible, but market forces have prevented widespread adoption.

Whether or not removing already-emitted carbon from the atmosphere is feasible, preventing future warming requires stopping the emissions of greenhouse gases. The most ambitious effort to forestall warming thus far is the 2016 Paris Agreement. This nonbinding international treaty aims to keep warming «well below 2 degrees Celsius above pre-industrial levels and to pursue efforts to limit the temperature increase even further to 1.5 degrees Celsius,» according to the United Nations. Each signatory to the treaty agreed to set their own voluntary greenhouse gas emission limits and to make them stricter over time. Climate scientists said that the emissions limits committed under the agreement wouldn’t keep warming as low as 1.5 or even 2 degrees C, but that it would be an improvement over the «business-as-usual» scenario.

Источники информации:

• http://www.epa.gov/ghgemissions/overview-greenhouse-gases
• http://www.nationalgeographic.com/environment/article/greenhouse-gases
• http://ecobnb.com/blog/2020/01/greehouse-gases-reduce-emissions/
• http://www.livescience.com/37821-greenhouse-gases.html

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Emissions Source	Examples of How Emissions Can be Reduced
Substitution of Ozone-Depleting Substances in Homes and Businesses