We’ve made some changes to EPA.gov. If the information you are looking for is not here, you may be able to find it on the EPA Web Archive or the January 19, 2017 Web Snapshot.

Greenhouse Gas Emissions

Sources of Greenhouse Gas Emissions

Overview

Pie chart of total U.S. greenhouse gas emissions by economic sector in 2015. 29 percent is from electricity, 27 percent is from transportation, 21 percent is from industry, 12 percent is from commercial and residential, and 9 percent is from agriculture.Total Emissions in 2015 = 6,587 Million Metric Tons of CO2 equivalent

Land Use, Land-Use Change, and Forestry in the United States is a net sink and offsets approximately 11.8 percent of these greenhouse gas emissions, not included in total above. All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2015.

Larger image to save or print.
Greenhouse gases trap heat and make the planet warmer. Human activities are responsible for almost all of the increase in greenhouse gases in the atmosphere over the last 150 years.1 The largest source of greenhouse gas emissions from human activities in the United States is from burning fossil fuels for electricity, heat, and transportation.

EPA tracks total U.S. emissions by publishing the Inventory of U.S. Greenhouse Gas Emissions and Sinks. This annual report estimates the total national greenhouse gas emissions and removals associated with human activities across the United States.

The primary sources of greenhouse gas emissions in the United States are:

  • Electricity production (29 percent of 2015 greenhouse gas emissions) – Electricity production generates the largest share of greenhouse gas emissions. Approximately 67 percent of our electricity comes from burning fossil fuels, mostly coal and natural gas.2
  • Transportation (27 percent of 2015 greenhouse gas emissions) – Greenhouse gas emissions from transportation primarily come from burning fossil fuel for our cars, trucks, ships, trains, and planes. Over 90 percent of the fuel used for transportation is petroleum based, which includes gasoline and diesel.3
  • Industry (21 percent of 2015 greenhouse gas emissions) – Greenhouse gas emissions from industry primarily come from burning fossil fuels for energy, as well as greenhouse gas emissions from certain chemical reactions necessary to produce goods from raw materials.
  • Commercial and Residential (12 percent of 2015 greenhouse gas emissions) – Greenhouse gas emissions from businesses and homes arise primarily from fossil fuels burned for heat, the use of certain products that contain greenhouse gases, and the handling of waste.
  • Agriculture (9 percent of 2015 greenhouse gas emissions) – Greenhouse gas emissions from agriculture come from livestock such as cows, agricultural soils, and rice production.
  • Land Use and Forestry (offset of 11.8 percent of 2015 greenhouse gas emissions) – Land areas can act as a sink (absorbing CO2 from the atmosphere) or a source of greenhouse gas emissions. In the United States, since 1990, managed forests and other lands have absorbed more CO2 from the atmosphere than they emit.

Emissions and Trends

Since 1990, U.S. greenhouse gas emissions have increased by about 4 percent. From year to year, emissions can rise and fall due to changes in the economy, the price of fuel, and other factors. In 2015, U.S. greenhouse gas emissions decreased compared to 2014 levels. This decrease was largely driven by a decrease in emissions from fossil fuel combustion, which was a result of multiple factors including substitution from coal to natural gas consumption in the electric power sector; warmer winter conditions that reduced demand for heating fuel in the residential and commercial sectors; and a slight decrease in electricity demand.

Line graph showing total U.S. greenhouse gas emissions for 1990 to 2015. Total emissions increased from about 6,400 million metric tons of carbon dioxide equivalents in 1990 to over 7,000 million in 1998, and decreased to around 6,600 million in 2015.All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2015.

Larger image to save or print.

References

1   IPCC (2007). Summary for Policymakers. In: Climate Change 2007: The Physical Science BasisExit Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
2   U.S. Energy Information Administration (2016). Electricity Explained - Basics.
3   Kahn Ribeiro, S., S. Kobayashi, M. Beuthe, J. Gasca, D. Greene, D. S. Lee, Y. Muromachi, P. J. Newton, S. Plotkin, D. Sperling, R. Wit, P. J. Zhou (2007). Transport and its infrastructure. In Climate Change 2007: Mitigation
Exit Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [B. Metz, O.R. Davidson, P.R. Bosch, R. Dave, L.A. Meyer (eds.)], Cambridge University Press, Cambridge, United Kingdom.

Top of Page

Electricity Sector Emissions

Pie chart of total U.S. greenhouse gas emissions by economic sector in 2015. 29 percent is from electricity, 27 percent is from transportation, 21 percent is from industry, 12 percent is from commercial and residential, and 9 percent is from agriculture.Total Emissions in 2015 = 6,587 Million Metric Tons of CO2 equivalent

Land Use, Land-Use Change, and Forestry in the United States is a net sink and offsets approximately 11.8 percent of these greenhouse gas emissions, not included in total above. All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2015.

Larger image to save or print.
The Electricity sector involves the generation, transmission, and distribution of electricity. Carbon dioxide (CO2) makes up the vast majority of greenhouse gas emissions from the sector, but smaller amounts of methane (CH4) and nitrous oxide (N2O) are also emitted. These gases are released during the combustion of fossil fuels, such as coal, oil, and natural gas, to produce electricity. Less than 1 percent of greenhouse gas emissions from the sector come from sulfur hexafluoride (SF6), an insulating chemical used in electricity transmission and distribution equipment.

Greenhouse Gas Emissions in the Electricity Sector by Fuel Source

Coal combustion is generally more carbon intensive than burning natural gas or petroleum for electricity. Although coal accounted for about 70 percent of CO2 emissions from the sector, it represented only about 34 percent of the electricity generated in the United States in 2015. Another 32 percent of electricity generated in 2015 was generated using natural gas, an increase relative to 2014. Petroleum accounted for less than 1 percent of electricity generation in 2015. The remaining generation in 2015 came from non-fossil fuel sources including nuclear (about 20 percent) and renewable sources (about 13 percent), which include hydroelectricity, biomass, wind, and solar.1 These other sources usually release fewer greenhouse gas emissions than fossil fuel combustion, if any emissions at all.

Emissions and Trends

In 2015, the electricity sector was the largest source of U.S. greenhouse gas emissions, accounting for about 29 percent of the U.S. total. Greenhouse gas emissions from electricity have increased by about 4 percent since 1990 as electricity demand has grown and fossil fuels have remained the dominant source for generation.

Line graph of greenhouse gas emissions from the electricity sector for 1990 to 2015. Emissions started around 1,800 million metric tons of carbon dioxide equivalents in 1990, peaked at nearly 2,500 million in 2007, and fell to 2,000 million in 2015. All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2015.

Larger image to save or print.

Greenhouse Gas Emissions by Electricity End-Use

Pie chart showing total U.S. Greenhouse Gas Emissions by Sector with Electricity Distributed. 33 percent is from Residential and Commercial, 29 percent is from industry, 27 percent is from transportation, and 9 percent is from agriculture.All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2015.

Larger image to save or print.
Electricity is consumed by other sectorsin homes, businesses, and factories. Therefore, it is possible to attribute the greenhouse gas emissions from electricity production to the sectors that use the electricity. Looking at greenhouse gas emissions by end-use sector can help us understand energy demand across sectors and changes in energy use over time.

When emissions from electricity are allocated to the end-use sector, industrial activities account for a much larger share of U.S. greenhouse gas emissions. Emissions from commercial and residential buildings also increase substantially when emissions from electricity are included, due to their relatively large share of electricity consumption (e.g., lighting and appliances).

Reducing Emissions from Electricity

There are a variety of opportunities to reduce greenhouse gas emissions associated with electricity generation, transmission, and distribution. The table shown below categorizes these opportunities and provides examples. For a more comprehensive list, see Chapter 7 of the Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate ChangeExit

Example Reduction Opportunities for the Electricity Sector
Type How Emissions Are Reduced Examples
Increased Efficiency of Power Plants and Fuel Switching Increasing efficiency of existing power plants by using advanced technologies or substituting fuels that combust more efficiently.
  • Converting a conventional coal-powered steam turbine into an advanced turbine that uses pulverized coal.
  • Converting a coal-powered turbine into a natural gas-powered turbine.
  • Converting a single-cycle turbine into a combined-cycle turbine.
Renewable Energy Using renewable energy sources rather than fossil fuel to generate electricity. Increasing the share of total electricity generated from wind, solar, hydro, and geothermal sources and from certain biofuel sources.
Increased Energy Efficiency (end-use) Reducing energy demand by increasing efficiency and conservation in homes, businesses, and industry. EPA's ENERGY STAR® partners removed over 300 million metric tons of greenhouse gases in 2014 alone, and saved consumers and businesses over $34 billion on their utility bills.
Nuclear Energy Generating electricity from nuclear processes rather than the combustion of fossil fuels. Building nuclear power plants as fossil fuel power plants are retired.
Carbon Capture Sequestration and Storage (CCS) Capturing CO2 as a byproduct of fossil fuel combustion before it enters the atmosphere and then transferring the CO2 to a long-term storage area, such as an underground geologic formation. Capturing CO2 from the stacks of a coal-fired power plant, and then transferring the CO2 via pipeline to a nearby abandoned oil field where the CO2 is injected underground. Learn more about CCS.

Reference

1. U.S. Energy Information Administration (2016). Electricity Explained - Basics.

Top of Page

Transportation Sector Emissions

Pie chart of total U.S. greenhouse gas emissions by economic sector in 2015. 29 percent is from electricity, 27 percent is from transportation, 21 percent is from industry, 12 percent is from commercial and residential, and 9 percent is from agriculture.Total Emissions in 2015 = 6,587 Million Metric Tons of CO2 equivalent

Land Use, Land-Use Change, and Forestry in the United States is a net sink and offsets approximately 11.8 percent of these greenhouse gas emissions, not included in total above. All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2015.

Larger image to save or print.
The Transportation sector includes the movement of people and goods by cars, trucks, trains, ships, airplanes, and other vehicles. The majority of greenhouse gas emissions from transportation are carbon dioxide (CO2) emissions resulting from the combustion of petroleum-based products, like gasoline, in internal combustion engines. The largest sources of transportation-related greenhouse gas emissions include passenger cars and light-duty trucks, including sport utility vehicles, pickup trucks, and minivans. These sources account for over half of the emissions from the sector. The remainder of greenhouse gas emissions comes from other modes of transportation, including freight trucks, commercial aircraft, ships, boats, and trains, as well as pipelines and lubricants.

Relatively small amounts of methane (CH4) and nitrous oxide (N2O) are emitted during fuel combustion. In addition, a small amount of hydrofluorocarbon (HFC) emissions are included in the Transportation sector. These emissions result from the use of mobile air conditioners and refrigerated transport.

Emissions and Trends

In 2015, greenhouse gas emissions from transportation accounted for about 27 percent of total U.S. greenhouse gas emissions, making it the second largest contributor of U.S. greenhouse gas emissions after the Electricity sector. In terms of the overall trend, from 1990 to 2015, total transportation emissions increased due, in large part, to increased demand for travel. The number of vehicle miles traveled (VMT) by light-duty motor vehicles (passenger cars and light-duty trucks) increased by approximately 40 percent from 1990 to 2015, as a result of a confluence of factors including population growth, economic growth, urban sprawl, and periods of low fuel prices. Between 1990 and 2004, average fuel economy among new vehicles sold annually declined, as sales of light-duty trucks increased. Starting in 2005, average new vehicle fuel economy began to increase while light-duty VMT grew only modestly for much of the period. Average new vehicle fuel economy has improved almost every year since 2005, and the truck share is about 43 percent of new vehicles in model year 2015.

Learn more about Greenhouse Gas Emissions from Transportation

Line graph of greenhouse gas emissions from transportation for 1990 to 2015. Emissions started just above 1,500 million metric tons of carbon dioxide equivalents in 1990, peaked around 2,000 million in 2005, and fell to 1,800 million in 2015.Emissions involved in the consumption of electricity for transportation activities are included above, but not shown separately (as was done for other sectors). These indirect emissions are negligible, accounting for less than 1 percent of the total emissions shown in the graph.

It is important to note that there was a change in methods between 2014 and 2015 used to estimate gasoline consumption in the transportation sector. The change does not impact total U.S. gasoline consumption. It mainly results in a shift in gasoline consumption from the transportation sector to industrial and commercial sectors for 2015. In the absence of this change, transportation greenhouse gas emissions would likely have been higher in 2015.  The change is discussed further in the Energy chapter in the Inventory of U.S. Greenhouse Gas Emissions and Sinks.

All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2015.

Larger image to save or print.

Reducing Emissions from Transportation

There are a variety of opportunities to reduce greenhouse gas emissions associated with transportation. The table shown below categorizes these opportunities and provides examples. For a more comprehensive list, see Chapter 8 of the Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate ChangeExit

EPA's light-duty vehicle greenhouse gas rules will save consumers $1.7 trillion at the pump by 2025, and eliminate 6 billion metric tons of greenhouse gas pollution.

Examples of Reduction Opportunities in the Transportation Sector
Type How Emissions Are Reduced Examples
Fuel Switching Using fuels that emit less CO2 than fuels currently being used. Alternative sources can include biofuels; hydrogen; electricity from renewable sources, such as wind and solar; or fossil fuels that are less CO2-intensive than the fuels that they replace.
Learn more about Alternative and Renewable Fuels.
  • Using public buses that are fueled by compressed natural gas rather than gasoline or diesel.
  • Using electric or hybrid automobiles, provided that the energy is generated from lower-carbon or non-fossil fuels.
  • Using renewable fuels such as low-carbon biofuels.
Improving Fuel Efficiency with Advanced Design, Materials, and Technologies Using advanced technologies, design, and materials to develop more fuel-efficient vehicles.

Learn about EPA's vehicle greenhouse gas rules.
  • Developing advanced vehicle technologies such as hybrid vehicles and electric vehicles, that can store energy from braking and use it for power later.
  • Reducing the weight of materials used to build vehicles.
  • Reducing the aerodynamic resistance of vehicles through better shape design.
Improving Operating Practices Adopting practices that minimize fuel use.
Improving driving practices and vehicle maintenance.
Learn about how the freight transportation industry can reduce emissions through EPA's SmartWay Program.
  • Reducing the average taxi time for aircraft.
  • Driving sensibly (avoiding rapid acceleration and braking, observing the speed limit).
  • Reducing engine-idling.
  • Improved voyage planning for ships, such as through improved weather routing, to increase fuel efficiency.
Reducing Travel Demand Employing urban planning to reduce the number of miles that people drive each day.
Learn about EPA's Smart Growth Program.

Reducing the need for driving through travel efficiency measures such as commuter, biking, and pedestrian programs. 
See a list of links to state, local, and regional travel-efficiency programs.
  • Building public transportation, sidewalks, and bike paths to increase lower-emission transportation choices.
  • Zoning for mixed use areas, so that residences, schools, stores, and businesses are close together, reducing the need for driving.

Top of Page

Industry Sector Emissions

Pie chart of total U.S. greenhouse gas emissions by economic sector in 2015. 29 percent is from electricity, 27 percent is from transportation, 21 percent is from industry, 12 percent is from commercial and residential, and 9 percent is from agriculture.Total Emissions in 2015 = 6,587 Million Metric Tons of CO2 equivalent   Land Use, Land-Use Change, and Forestry in the United States is a net sink and offsets approximately 11.8 percent of these greenhouse gas emissions, not included in total above. All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2015.

Larger image to save or print.
The Industry sector produces the goods and raw materials we use every day. The greenhouse gases emitted during industrial production are split into two categories: direct emissions that are produced at the facility, and indirect emissions that occur off site, but are associated with the facility's use of energy.

Direct emissions are produced by burning fuel for power or heat, through chemical reactions, and from leaks from industrial processes or equipment. Most direct emissions come from the consumption of fossil fuels for energy. A smaller amount, roughly a third, come from leaks from natural gas and petroleum systems, the use of fuels in production (e.g., petroleum products used to make plastics), and chemical reactions during the production of chemicals, iron and steel, and cement.

Indirect emissions are produced by burning fossil fuel at a power plant to make electricity, which is then used by an industrial facility to power industrial buildings and machinery.

More information about facility-level emissions from large industrial sources is available through EPA's Greenhouse Gas Reporting Program's data publication tool. National-level information about emissions from industry as a whole can be found in the sections on Fossil Fuel Combustion and the Industrial Processes chapter in the Inventory of U.S. Greenhouse Gas Emissions and Sinks.

Emissions and Trends

In 2015, direct industrial greenhouse gas emissions accounted for approximately 21 percent of total U.S. greenhouse gas emissions, making it the third largest contributor to U.S. greenhouse gas emissions, after the Electricity and Transportation sectors. If both direct and indirect emissions associated with electricity use are included, industry's share of total U.S. greenhouse gas emissions in 2015 was 29 percent, making it the largest contributor of greenhouse gases of any sector. Greenhouse gas emissions from industry have declined by almost 13 percent since 1990, while emissions from most other sectors have increased.

Line graph of carbon emissions from land use, land use change, and forestry for 1990 to 2015. Emissions started around negative 530 million metric tons of carbon dioxide equivalents and generally rise to negative 470 million in 2015.All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2015.

Larger image to save or print.

Reducing Emissions from Industry

There are a wide variety of industrial activities that cause greenhouse gas emissions, and many opportunities to reduce them. The table shown below provides some examples of opportunities for industry to reduce emissions. For a more comprehensive list, see Chapter 10 of the Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Exit

Examples of Reduction Opportunities for the Industry Sector
Type How Emissions Are Reduced Examples
Energy Efficiency Upgrading to more efficient industrial technology.
EPA's ENERGY STAR® program helps industries become more energy-efficient.
Identifying the ways that manufacturers(87 pp, 1 M, About PDF) can use less energy to light and heat factories or to run equipment.
Fuel Switching Switching to fuels that result in less CO2 emissions but the same amount of energy, when combusted. Using natural gas instead of coal to run machinery.
Recycling Producing industrial products from materials that are recycled or renewable, rather than producing new products from raw materials. Using scrap steel and scrap aluminum as opposed to smelting new aluminum or forging new steel.
Training and Awareness

Making companies and workers aware of the steps to reduce or prevent emissions leaks from equipment.
EPA has a variety of voluntary programs that provide resources for training and other steps for reducing emissions. EPA supports programs for the aluminumsemiconductor, and magnesium industries.

Instituting handling policies and procedures for perfluorocarbons (PFCs), hydrofluorocarbons (HFCs), and sulfur hexafluoride (SF6) that reduce occurrences of accidental releases and leaks from containers and equipment.
 

Top of Page

Commercial and Residential Sector Emissions

Pie chart of total U.S. greenhouse gas emissions by economic sector in 2015. 29 percent is from electricity, 27 percent is from transportation, 21 percent is from industry, 12 percent is from commercial and residential, and 9 percent is from agriculture.Total Emissions in 2015 = 6,587 Million Metric Tons of CO2 equivalent  Land Use, Land-Use Change, and Forestry in the United States is a net sink and offsets approximately 11.8 percent of these greenhouse gas emissions, not included in total above. All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2015.

Larger image to save or print
The residential and commercial sectors include all homes and commercial businesses (excluding agricultural and industrial activities). Greenhouse gas emissions from this sector come from direct emissions including fossil fuel combustion for heating and cooking needs, management of waste and wastewater, and leaks from refrigerants in homes and businesses as well as indirect emissions that occur offsite but are associated with use of electricity consumed by homes and businesses.

Direct emissions are produced from residential and commercial activities in a variety of ways:

  • Combustion of natural gas and petroleum products for heating and cooking needs emits carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Emissions from natural gas consumption represent about 76 percent of the direct fossil fuel CO2 emissions from the residential and commercial sectors. Coal consumption is a minor component of energy use in both of these sectors.
  • Organic waste sent to landfills emits CH4.
  • Wastewater treatment plants emit CH4 and N2O.
  • Fluorinated gases (mainly hydrofluorocarbons, or HFCs) used in air conditioning and refrigeration systems can be released during servicing or from leaking equipment.

Indirect emissions are produced by burning fossil fuel at a power plant to make electricity, which is then used in residential and commercial activities such as lighting and for appliances.

More national-level information about emissions from the residential and commercial sectors can be found in the U.S. Inventory's Energy and Trends chapters.

Emissions and Trends

In 2015, direct greenhouse gas emissions from homes and businesses accounted for approximately 12 percent of total U.S. greenhouse gas emissions. Greenhouse gas emissions from homes and businesses have generally been increasing since 1990, but vary from year to year based on short-term fluctuations in energy consumption caused by weather conditions. Total residential and commercial greenhouse gas emissions in 2015 have increased by about 14 percent since 1990. Greenhouse gas emissions from on-site energy combustion in homes and businesses have increased by about 6 percent since 1990. Additionally, indirect emissions from electricity use by homes and businesses have increased by 19 percent since 1990, due to increasing electricity consumption for lighting, heating, air conditioning, and appliances.

Line graph of direct and indirect greenhouse gas emissions from homes and businesses for 1990 to 2015. There are three lines - for total emissions, direct emissions, and indirect emissions from electricity. All three lines trend upwards.All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2015.

Larger image to save or print.

Reducing Emissions from Homes and Businesses

The table shown below provides some examples of opportunities to reduce emissions from homes and businesses. For a more comprehensive list of options and a detailed assessment of how each option affects different gases, see Chapter 9 and Chapter 12 of the Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate ChangeExit

Examples of Reduction Opportunities in the Residential and Commercial Sector
Type How Emissions Are Reduced Examples
Homes and Commercial Buildings Reducing energy use through energy efficiency. Homes and commercial buildings use large amounts of energy for heating, cooling, lighting, and other functions. "Green building" techniques and retrofits can allow new and existing buildings to use less energy to accomplish the same functions, leading to fewer greenhouse gas emissions. Techniques to improve building energy efficiency include better insulation; more energy-efficient heating, cooling, ventilation, and refrigeration systems; efficient fluorescent lighting; passive heating and lighting to take advantage of sunlight; and the purchase of energy-efficient appliances and electronics. Learn more about ENERGY STAR®.
Wastewater Treatment Making water and wastewater systems more energy-efficient. Drinking water and wastewater systems account for approximately 3 percent to 4 percent of energy use in the United States. Studies estimate potential savings of 15 percent to 30 percent that are "readily achievable" in water and wastewater plants.1
Learn more about Energy Efficiency for Water and Wastewater Utilities.
Waste Management Reducing solid waste sent to landfills.
Capturing and using methane produced in current landfills.
Landfill gas is the natural byproduct of the decomposition of solid waste in landfills. It primarily consists of CO2 and CH4.
Well established, low-cost methods to reduce greenhouse gases from consumer waste exist, including recycling programs, waste reduction programs, and landfill methane capture programs.
Refrigeration Reducing leakage from refrigeration equipment.
Using refrigerants with lower global warming potentials.
Commonly used refrigerants include ozone-depleting hydrochlorofluorocarbon (HCFC) refrigerants, often HCFC-22, and blends consisting entirely or primarily of hydrofluorocarbons (HFCs), both of which are potent greenhouse gases. In recent years there have been several advancements in refrigeration technology that can help food retailers reduce both refrigerant charges and refrigerant emissions.
Learn more about EPA's GreenChill Program to reduce greenhouse gas emissions from commercial refrigerators.

References

1   EPA (2012). Energy Efficiency for Water and Wastewater Utilities. Accessed 03/13/2012

Top of Page

Agriculture Sector Emissions

Pie chart of total U.S. greenhouse gas emissions by economic sector in 2015. 29 percent is from electricity, 27 percent is from transportation, 21 percent is from industry, 12 percent is from commercial and residential, and 9 percent is from agriculture.Total Emissions in 2015 = 6,587 Million Metric Tons of CO2 equivalent

 Land Use, Land-Use Change, and Forestry in the United States is a net sink and offsets approximately 11.8 percent of these greenhouse gas emissions, not included in total above. All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2015.

Larger image to save or print.
Agricultural activities – crop and livestock production for food – contribute to emissions in a variety of ways:

  • Various management practices on agricultural soils can lead to increased availability of nitrogen in the soil and result in emissions of nitrous oxide (N2O). Specific activities that contribute to N2O emissions from agricultural lands include the application of synthetic and organic fertilizers, the growth of nitrogen-fixing crops, the drainage of organic soil, and irrigation practices. Management of agricultural soils accounts for over half of the emissions from the Agriculture economic sector.*
  • Livestock, especially ruminants such as cattle, produce methane (CH4) as part of their normal digestive processes. This process is called enteric fermentation, and it represents almost one third of the emissions from the Agriculture economic sector.
  • The way in which manure from livestock is managed also contributes to CH4 and N2O emissions. Different manure treatment and storage methods affect how much of these greenhouse gases are produced. Manure management accounts for about 15 percent of the total greenhouse gas emissions from the Agriculture economic sector in the United States.
  • Smaller sources of agricultural emissions include rice cultivation, which produces CH4, and burning crop residues, which produces CH4 and N2O.

More national-level information about emissions from agriculture can be found in the agriculture chapter in the Inventory of U.S. Greenhouse Gas Emissions and Sinks.

* Management of agricultural soils can also lead to emissions or sequestration of carbon dioxide (CO2). However, these emissions are included under the Land Use, Land-Use Change, and Forestry sector.

Emissions and Trends

In 2015, greenhouse gas emissions from the agriculture economic sector accounted for approximately 9 percent of total U.S. greenhouse gas emissions. Greenhouse gas emissions from agriculture have increased by approximately 8 percent since 1990. One driver for this increase has been the 64 percent growth in combined CH4 and N2O emissions from livestock manure management systems, reflecting the increased use of emission-intensive liquid systems over this time period. Emissions from other agricultural sources have either remained flat or changed by a relatively small amount since 1990.

Line graph of greenhouse gas emissions from agriculture for 1990 to 2015. There are three lines - for total emissions, direct emissions, and indirect emissions from electricity. Total and direct emissions trend upwards; indirect stay roughly constant.All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2015.

Larger image to save or print.

Reducing Emissions from Agriculture

The table shown below provides some examples of opportunities to reduce emissions from agriculture. For a more comprehensive list of options and a detailed assessment of how each option affects different gases, see Chapter 11 of the Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate ChangeExit

Examples of Reduction Opportunities for the Agriculture Sector
Type How Emissions Are Reduced Examples
Land and Crop Management Adjusting the methods for managing land and growing crops.
  • Fertilizing crops with the precise amount of nitrogen required for crop production, since over-application of nitrogen can lead to higher N2O emissions without enhancing crop production.
  • Draining water from wetland rice soils during the growing season to reduce CH4 emissions.
Livestock Management Adjusting feeding practices and other management methods to reduce the amount of CH4 resulting from enteric fermentation.
  • Improving pasture quality to increase animal productivity, which can reduce the amount of CH4 emitted per unit of animal product. Also, increased productivity in livestock can be introduced through improved breeding practices.
Manure Management
  • Controlling the way in which manure decomposes to reduce N2O and CH4 emissions.
  • Capturing CH4 from manure decomposition to produce renewable energy.
  • Handling manure as a solid or depositing it on pasture rather than storing it in a liquid-based system such as a lagoon. This would likely reduce CH4 emissions but may increase N2O emissions.
  • Storing manure in anaerobic containment areas to maximize CH4 production and then capturing the CH4 to use as an energy substitute for fossil fuels.
  • For more information, see EPA's AgSTAR Program, a voluntary outreach and education program that promotes recovery and use of methane from animal manure.

Top of Page

Land Use, Land-Use Change, and Forestry Sector Emissions

Plants absorb carbon dioxide (CO2) from the atmosphere as they grow, and they store some of this carbon throughout their lifetime. Soils can also store some of the carbon from these plants depending on how the soil is managed and other environmental conditions (e.g., climate). This storage of carbon in plants and soils is called biological carbon sequestration. Because biological sequestration takes CO2 out of the atmosphere, it is also called a greenhouse gas "sink."

Emissions or sequestration of CO2 can occur as land uses change. Carbon dioxide is exchanged between the atmosphere and the plants and soils on land, for example, as cropland is converted into grassland, as new lands are cultivated and become cropland, or as forests grow. In addition, using biological feedstocks (such as energy crops or wood) for purposes such as electricity generation, as inputs to processes that create liquid fuels, or as building materials can lead to emissions or sequestration.

In the United States overall, since 1990, land use, land-use change, and forestry activities have resulted in more removal of CO2 from the atmosphere than emissions. Because of this, the Land Use, Land-Use Change, and Forestry (LULUCF) sector in the United States is considered a net sink, rather than a source, of CO2 over this time-period. In many areas of the world, the opposite is true, particularly in countries where large areas of forest land are cleared, often for conversion to agricultural purposes or for settlements. In these situations, the LULUCF sector can be a net source of greenhouse gas emissions.

Emissions and Trends

In 2015, the net CO2 removed from the atmosphere from the LULUCF sector offset about 12 percent of total U.S. greenhouse gas emissions. Total carbon sequestration in the LULUCF sector decreased by approximately 6 percent between 1990 and 2015. This decrease was primarily due to a decrease in the rate of net carbon accumulation in forests and an increase in emissions from land converted to settlements.

Line graph of carbon emissions from land use, land use change, and forestry for 1990 to 2015. Emissions started around negative 530 million metric tons of carbon dioxide equivalents and generally rise to negative 470 million in 2015.*Note: The LULUCF sector is a net "sink" of emissions in the United States (e.g., more greenhouse gas emissions are sequestered than emitted from land use activities), so net greenhouse gas emissions from LULUCF are negative. 

All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2015.

Larger image to save or print.

Reducing Emissions and Enhancing Sinks from Land Use, Land-Use Change, and Forestry

In the LULUCF sector, opportunities exist to reduce emissions and increase the potential to sequester carbon from the atmosphere by enhancing sinks. The table shown below provides some examples of opportunities for both reducing emissions and enhancing sinks. For a more comprehensive list, see Chapter 11 of the Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate ChangeExit

Examples of Reduction Opportunities in the LULUCF Sector
Type How Emissions Are Reduced or Sinks Are Enhanced  Examples
Change in Uses of Land Increasing carbon storage by using land differently or maintaining carbon storage by avoiding land degradation.
  • Minimizing the conversion of forest land to other land uses, such as settlements, croplands, or grasses.
Changes in Land Management Practices Improving management practices on existing land-use types.
  • Utilizing reduced tillage practices on cropland and improved grazing management practices on grassland.
  • Planting after natural or human-induced forest disturbances to accelerate vegetation growth and minimize soil carbon losses.

Top of Page

6,587 million metric tons of CO2 equivalent – 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 percent) than a U.S. "short" ton.

Greenhouse gas 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.

The GWP values appearing in the Emissions Web pages reflect the values used in the U.S. Inventory, which are drawn from the IPCC's Second Assessment Report (SAR). For further discussion of GWPs and an estimate of greenhouse gas emissions using updated GWPs, see Annex 6 of the U.S. Inventory and the IPCC's discussion on GWPsExit