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Greenhouse Gas Emissions

U.S. Greenhouse Gas Inventory Report: 1990-2014

About the Emissions Inventory

Greenhouse Gas Inventory Data Explorer

Explore emissions data with EPA's interactive tool.

EPA develops an annual report called the Inventory of U.S. Greenhouse Gas Emissions and Sinks (Inventory). This report tracks total annual U.S. emissions and removals by source, 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. EPA also collects greenhouse gas emissions data from individual facilities and suppliers of certain fossil fuels and industrial gases through the Greenhouse Gas Reporting Program.

The national greenhouse gas inventory is submitted to the United Nations in accordance with the Framework Convention on Climate Change. Exit In preparing the annual emissions inventory report, EPA collaborates with hundreds of experts representing more than a dozen U.S. government agencies, academic institutions, industry associations, consultants, and environmental organizations.

Related Links

Fast Facts

Stakeholder Webinar: Waste Sector Data and Methodology in the Inventory

Natural Gas Systems Data in the Inventory

U.S. Greenhouse Gas Inventory Report Archives

Greenhouse Gas Reporting Program

Relationship between the Inventory and the Greenhouse Gas Reporting Program

Overview of Greenhouse Gases and Sources of Emissions

Key findings from the 1990–2014 U.S. Inventory include:

In 2014, U.S. greenhouse gas emissions totaled 6,870 million metric tons of carbon dioxide equivalents.

U.S. emissions increased by 1 percent from 2013 to 2014. Recent trends can be attributed to multiple factors driving increased fuel use including year-to-year changes in the prevailing weather and an increase in miles traveled by on-road vehicles.

Greenhouse gas emissions in 2014 were 9 percent below 2005 levels.

The graphs below provide an overview of greenhouse gas emissions in the United States based on information from the Inventory. Click the links below each chart to learn more about each of these topics. See our Fast Facts Fact Sheet for an overview of the GHG emissions data from the report.

Overview of Greenhouse Gases

<img alt="Pie chart of total U.S. greenhouse gas emissions by economic sector in 2014. 30 percent is from electricity, 26 percent is from transportation, 21 percent is from industry, 12 percent is from commercial and residential, and 9 percent is from agriculture." title="Pie chart of total U.S. greenhouse gas emissions by economic sector in 2014. 30 percent is from electricity, 26 percent is from transportation, 21 percent is from industry, 12 percent is from commercial and residential, and 9 percent is from agriculture." height="414" width="414" class="media-element file-full" typeof="foaf:Image" src="/sites/production/files/styles/large/public/2016-06/sources-overview_2014-new.png" />Sources of Greenhouse Gas Emissions

See the Data

EPA has developed an interactive tool that provides access to data from the national greenhouse gas inventory. Visit the Greenhouse Gas Inventory Data Explorer to create customized graphs, examine trends over time, and download the data.

The graphs below are examples from EPA’s Greenhouse Gas Inventory Data Explorer. Click either image to enter the tool and explore an interactive version of the graph.

Full Report

View or download the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2014 (April 2016), including an executive summary, individual chapters, report tables, and annexes.

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Greenhouse Gas Emissions

Sources of Greenhouse Gas Emissions

Overview

Electricity

Transportation

Industry

Commercial/

			Residential

Agriculture

Land Use/

			Forestry

Overview

<img alt="Pie chart of total U.S. greenhouse gas emissions by economic sector in 2014. 30 percent is from electricity, 26 percent is from transportation, 21 percent is from industry, 12 percent is from commercial and residential, and 9 percent is from agriculture." title="Pie chart of total U.S. greenhouse gas emissions by economic sector in 2014. 30 percent is from electricity, 26 percent is from transportation, 21 percent is from industry, 12 percent is from commercial and residential, and 9 percent is from agriculture." height="440" width="411" class="right media-element file-medium right" typeof="foaf:Image" src="/sites/production/files/styles/medium/public/2016-05/ghge-sources-overview.png" />Total Emissions in 2014 = 6,870 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 percent of these greenhouse gas emissions.

	All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2014.

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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 (30 percent of 2014 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 (26 percent of 2014 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 2014 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 2014 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 2014 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 percent of 2014 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 7 percent. From year to year, emissions can rise and fall due to changes in the economy, the price of fuel, and other factors. In 2014, U.S. greenhouse gas emissions increased compared to 2013 levels. This increase was due to a number of factors, including: cold winter conditions resulting in an increase in fuel demand, especially in residential and commercial sectors; an increase in transportation emissions resulting from an increase in vehicle miles traveled; and an increase in industrial production across multiple sectors that also resulted in increases in industrial sector emissions.

<img alt="U.S. GHG emissions, 1990-2014: Emissions steadily increase from ~6,400 million metric tons of carbon dioxide equivalents in 1990 to over 7000 in 1997. Between 2007-2009, emissions are ~6800, followed by ~7000 in 2010-2011, ~6000 in 2012, & ~6900 in 2014." title="U.S. GHG emissions, 1990-2014: Emissions steadily increase from ~6,400 million metric tons of carbon dioxide equivalents in 1990 to over 7000 in 1997. Between 2007-2009, emissions are ~6800, followed by ~7000 in 2010-2011, ~6000 in 2012, & ~6900 in 2014." height="550" width="928" class="center media-element file-full" typeof="foaf:Image" src="/sites/production/files/styles/large/public/2016-05/ghge-total-all.png" />All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2014.

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To learn about projected greenhouse gas emissions to 2020, visit the U.S. Climate Action Report 2014.(310 pp, 23 M, About PDF)

References

1   IPCC (2007). Summary for Policymakers. In: Climate Change 2007: The Physical Science Basis. Exit 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.

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Electricity Sector Emissions

<img alt="Pie chart of total U.S. greenhouse gas emissions by economic sector in 2014. 30 percent is from electricity, 26 percent is from transportation, 21 percent is from industry, 12 percent is from commercial and residential, and 9 percent is from agriculture." title="Pie chart of total U.S. greenhouse gas emissions by economic sector in 2014. 30 percent is from electricity, 26 percent is from transportation, 21 percent is from industry, 12 percent is from commercial and residential, and 9 percent is from agriculture." height="457" width="412" class="right media-element file-medium right" typeof="foaf:Image" src="/sites/production/files/styles/medium/public/2016-05/sources-electricity-1.png" />Total Emissions in 2014 = 6,870 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 percent of these greenhouse gas emissions.

	All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2014.

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 accounts for about 77 percent of CO2 emissions from the sector, it represents about 39 percent of the electricity generated in the United States. About 27 percent of electricity generated in 2014 was generated using natural gas, an increase relative to 2013. Petroleum accounts for approximately 1 percent of electricity generation. The remaining generation comes from nuclear (about 19 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 2014, the electricity sector was the largest source of U.S. greenhouse gas emissions, accounting for about 30 percent of the U.S. total. Greenhouse gas emissions from electricity have increased by about 12 percent since 1990 as electricity demand has grown and fossil fuels have remained the dominant source for generation.

To learn about projected greenhouse gas emissions to 2020, visit the U.S. Climate Action Report 2014(310 pp, 23 M, About PDF).

Note: All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2014.

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Greenhouse Gas Emissions by Electricity End-Use

<img alt="Pie chart showing total U.S. Greenhouse Gas Emissions by Sector with Electricity Distributed. 34 percent is from Residential and Commercial, 29 percent is from industry, 26 percent is from transportation, and 10 percent is from agriculture." title="Pie chart showing total U.S. Greenhouse Gas Emissions by Sector with Electricity Distributed. 34 percent is from Residential and Commercial, 29 percent is from industry, 26 percent is from transportation, and 10 percent is from agriculture." height="416" width="411" class="right media-element file-medium right" typeof="foaf:Image" src="/sites/production/files/styles/medium/public/2016-05/sources-electricity-3_0.png" />Note: All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2014.

Larger image to save or print.Electricity is consumed by other sectors—in 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 Change. Exit

Under the president's Climate Action Plan, EPA is taking action to reduce emissions from power plants. Learn More.

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 (2014). Electricity Explained - Basics.

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Transportation Sector Emissions

<img alt="Pie chart of total U.S. greenhouse gas emissions by economic sector in 2014. 30 percent is from electricity, 26 percent is from transportation, 21 percent is from industry, 12 percent is from commercial and residential, and 9 percent is from agriculture." title="Pie chart of total U.S. greenhouse gas emissions by economic sector in 2014. 30 percent is from electricity, 26 percent is from transportation, 21 percent is from industry, 12 percent is from commercial and residential, and 9 percent is from agriculture." height="467" width="405" class="right media-element file-medium right" typeof="foaf:Image" src="/sites/production/files/styles/medium/public/2016-05/sources-transportation-1.png" />Total Emissions in 2014 = 6,870 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 percent of these greenhouse gas emissions.

	All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2014.

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

Related Links

Transportation and Climate

EPA and U.S. DOE Fuel Economy

SmartWay

On The Road

Smart Growth

Renewable Fuel Standard

U.S. Inventory's section on Fossil Fuel Combustion

In 2014, greenhouse gas emissions from transportation accounted for about 26 percent of total U.S. greenhouse gas emissions, making it the second largest contributor of U.S. greenhouse gas emissions after the Electricity sector. Greenhouse gas emissions from transportation have increased by about 17 percent since 1990. This historical increase is largely due to increased demand for travel and the limited gains in fuel efficiency across the U.S. vehicle fleet. The number of vehicle miles traveled by passenger cars and light-duty trucks increased 37 percent from 1990 to 2014. The increase in travel miles is attributed to several factors, including population growth, economic growth, urban sprawl, and low fuel prices during the beginning of this period. Between 1990 and 2004, average fuel economy among new vehicles sold annually declined, as sales of light-duty trucks increased. However, new vehicle fuel economy began to improve in 2005, largely due to a lower light-duty truck market share and higher fuel economy standards.

Learn more about Greenhouse Gas Emissions from Transportation. To learn about projected greenhouse gas emissions to 2020, visit the U.S. Climate Action Report 2014(310 pp, 23 M, About PDF).

<img alt="Line graph of greenhouse gas emissions from transportation for 1990 to 2014. The GHG emissions started just above 1,500 MMtCO2e in 1990, and rose to a peak of just above 2,000 million in 2005. It ends just above 1,800 MMtCO2e." title="Line graph of greenhouse gas emissions from transportation for 1990 to 2014. The GHG emissions started just above 1,500 MMtCO2e in 1990, and rose to a peak of just above 2,000 million in 2005. It ends just above 1,800 MMtCO2e." height="574" width="928" class="center media-element file-full" typeof="foaf:Image" src="/sites/production/files/styles/large/public/2016-05/sources-transportation-2.png" />Note: 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.

Note: All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2014.

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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 Change. Exit

EPA's 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.

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Industry Sector Emissions

<img alt="Pie chart of total U.S. greenhouse gas emissions by economic sector in 2014. 30 percent is from electricity, 26 percent is from transportation, 21 percent is from industry, 12 percent is from commercial and residential, and 9 percent is from agriculture." title="Pie chart of total U.S. greenhouse gas emissions by economic sector in 2014. 30 percent is from electricity, 26 percent is from transportation, 21 percent is from industry, 12 percent is from commercial and residential, and 9 percent is from agriculture." height="457" width="412" class="right media-element file-medium right" typeof="foaf:Image" src="/sites/production/files/styles/medium/public/2016-05/sources-industry-1.png" />Total Emissions in 2014 = 6,870 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 percent of these greenhouse gas emissions.

	All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2014.

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 2014, 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 2014 was 29 percent, making it the largest contributor of greenhouse gases of any sector. Greenhouse gas emissions from industry have declined by almost 10 percent since 1990, while emissions from most other sectors have increased.

To learn about projected greenhouse gas emissions to 2020, visit the U.S. Climate Action Report 2014.(310 pp, 23 M, About PDF)

<img alt="Direct & indirect GHG emissions from industry electricity-consumption for 1990-2014: In 1990, total emissions are ~2,250 million metric tons of CO2 equivalents. Total emissions peak at ~2,400 in 1998, trough at ~1,850 in 2009, & reach ~2,000 in 2014." title="Direct & indirect GHG emissions from industry electricity-consumption for 1990-2014: In 1990, total emissions are ~2,250 million metric tons of CO2 equivalents. Total emissions peak at ~2,400 in 1998, trough at ~1,850 in 2009, & reach ~2,000 in 2014." height="589" width="928" class="center media-element file-full" typeof="foaf:Image" src="/sites/production/files/styles/large/public/2016-05/sources-industry-2.png" />All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2014.

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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 aluminum, semiconductor, 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.

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Commercial and Residential Sector Emissions

<img alt="Pie chart of total U.S. greenhouse gas emissions by economic sector in 2014. 30 percent is from electricity, 26 percent is from transportation, 21 percent is from industry, 12 percent is from commercial and residential, and 9 percent is from agriculture." title="Pie chart of total U.S. greenhouse gas emissions by economic sector in 2014. 30 percent is from electricity, 26 percent is from transportation, 21 percent is from industry, 12 percent is from commercial and residential, and 9 percent is from agriculture." height="466" width="416" class="right media-element file-medium right" typeof="foaf:Image" src="/sites/production/files/styles/medium/public/2016-05/sources-commercial.png" />Total Emissions in 2014 = 6,870 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 percent of these greenhouse gas emissions.

	All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2014.

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 fossil fuel combustion for heating and cooking needs, management of waste and wastewater, and leaks from refrigerants in homes and businesses. Indirect emissions, resulting from electricity consumed by homes and businesses, are discussed on the Electricity sector page.

Residential and commercial activities contribute to emissions 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 81 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.

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 2014, 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 2014 have increased by about 11 percent since 1990. Greenhouse gas emissions from on-site energy combustion in homes and businesses have increased by about 11 percent since 1990. Additionally, indirect emissions from electricity use by homes and businesses have increased by 27 percent since 1990, due to increasing electricity consumption for lighting, heating, air conditioning, and appliances.

To learn about projected greenhouse gas emissions to 2020, visit the U.S. Climate Action Report 2014.(310 pp, 23 M, About PDF)

<img alt="Direct & indirect GHG emissions from homes & businesses for 1990-2014: Direct emissions remain relatively constant over the time span, at 750-850 million metric tons of CO2 equivalents. Total emissions increase from ~1,900 in 1990 to ~2,300 in 2014." title="Direct & indirect GHG emissions from homes & businesses for 1990-2014: Direct emissions remain relatively constant over the time span, at 750-850 million metric tons of CO2 equivalents. Total emissions increase from ~1,900 in 1990 to ~2,300 in 2014." height="553" width="928" class="center media-element file-full" typeof="foaf:Image" src="/sites/production/files/styles/large/public/2016-05/sources-commercial-2.png" />All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2014.

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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 Change. Exit

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.

Learn about EPA's waste reduction and resource conservation efforts.

Learn more about climate change and waste.

Learn about EPA's Landfill Methane Outreach Program, which promotes the recovery and use of landfill gas.

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

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Agriculture Sector Emissions

<img alt="Pie chart of total U.S. greenhouse gas emissions by economic sector in 2014. 30 percent is from electricity, 26 percent is from transportation, 21 percent is from industry, 12 percent is from commercial and residential, and 9 percent is from agriculture." title="Pie chart of total U.S. greenhouse gas emissions by economic sector in 2014. 30 percent is from electricity, 26 percent is from transportation, 21 percent is from industry, 12 percent is from commercial and residential, and 9 percent is from agriculture." height="465" width="419" class="right media-element file-medium right" typeof="foaf:Image" src="/sites/production/files/styles/medium/public/2016-05/sources-agriculture.png" />Total Emissions in 2014 = 6,870 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 percent of these greenhouse gas emissions.

	All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2014.

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Agricultural activities – the cultivation of crops and livestock for food – contribute to emissions in a variety of ways:

Various management practices for agricultural soils can lead to production and emission of nitrous oxide (N2O). The large number of different activities that can contribute to N2O emissions from agricultural lands range from fertilizer application to methods of irrigation and tillage. Management of agricultural soils accounts for over half of the emissions from the Agriculture sector.*

Livestock, especially cattle, produce methane (CH4) as part of their digestion. This process is called enteric fermentation, and it represents almost one third of the emissions from the Agriculture sector.

The way in which manure from livestock is managed also contributes to CH4 and N2O emissions. Manure storage methods and the amount of exposure to oxygen and moisture can affect how these greenhouse gases are produced. Manure management accounts for about 14 percent of the total greenhouse gas emissions from the Agriculture sector in the United States.

Smaller sources of emissions include rice cultivation, which produces CH4, and burning crop residues, which produce 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 of carbon dioxide (CO2). However, these emissions are included under the Land Use, Land-Use Change, and Forestry sector.

Emissions and Trends

In 2014, greenhouse gas emissions from agriculture accounted for approximately 9 percent of total U.S. greenhouse gas emissions. Greenhouse gas emissions from agriculture have increased by approximately 11 percent since 1990. One driver for this increase has been the 54 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 agricultural soil management have also increased by about 5 percent since 1990. Emissions from other agricultural sources have either remained flat or changed by a relatively small amount since 1990.

To learn about projected greenhouse gas emissions to 2020, visit the U.S. Climate Action Report 2014.(310 pp, 23 M, About PDF)

<img alt="GHG emissions from agriculture for 1990-2014: Indirect emissions remain relatively constant over the time span, at ~65 million metric tons of CO2 equivalents. Direct emissions start at ~560 in 1990, and peak at ~635 in 2012. 2014 total emissions are ~690." title="GHG emissions from agriculture for 1990-2014: Indirect emissions remain relatively constant over the time span, at ~65 million metric tons of CO2 equivalents. Direct emissions start at ~560 in 1990, and peak at ~635 in 2012. 2014 total emissions are ~690." height="588" width="928" class="center media-element file-full" typeof="foaf:Image" src="/sites/production/files/styles/large/public/2016-05/sources-agriculture-1.png" />All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2014.

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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 Change. Exit

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, since less efficient nitrogen application can lead to higher N2O emissions.

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 can be accomplished through breeding.

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.

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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 the carbon throughout their lifetime. Soils can also store CO2, depending on how the soil is managed. 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. For example, CO2 is exchanged between the atmosphere and the plants and soils on land as former cropland is converted into grassland, as new areas 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, input to processes that create liquid fuels, or 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 period. In many areas of the world, the opposite is true: In countries where large areas of forest land are cleared, often for agricultural purposes or for settlements, the LULUCF sector can be a net source of greenhouse gas emissions.

More national-level information about land use, land-use change, and forestry is available from the Land Use, Land-Use Change, and Forestry chapter in the Inventory of U.S. Greenhouse Gas Emissions and Sinks.

See EPA's Global Greenhouse Gas emissions page for more information about global greenhouse gas emissions from land use and forestry activities.

For more information about global emissions from land use and forestry activities, see the Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Exit

Emissions and Trends

In 2014, the net CO2 removed from the atmosphere from the LULUCF sector offset about 11 percent of total U.S. greenhouse gas emissions. Forests (including vegetation, soils, and harvested wood) accounted for approximately 87 percent of the total 2014 LULUCF CO2 removals.

The net carbon sequestration by the LULUCF sector has increased by about 5 percent since 1990, largely as a result of changes in the land area of forests and improved forest management.

To learn about projected greenhouse gas emissions to 2020, visit the U.S. Climate Action Report 2014.(310 pp, 23 M, About PDF)

<img alt="GHG emissions from land use, land use change, & forestry for 1990-2014: Emissions start at -740 million metric tons of CO2 equivalent and peak at -660 in 2002. From 2002 onward, emissions drop quickly to a low of -770 in 2010, and ends at -760 in 2014." title="GHG emissions from land use, land use change, & forestry for 1990-2014: Emissions start at -740 million metric tons of CO2 equivalent and peak at -660 in 2002. From 2002 onward, emissions drop quickly to a low of -770 in 2010, and ends at -760 in 2014." height="641" width="928" class="center media-element file-full" typeof="foaf:Image" src="/sites/production/files/styles/large/public/2016-05/sources-lulucf.png" />*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: 1990–2014.

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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 Change. Exit

Examples of Reduction Opportunities in the LULUCF Sector

Type
					How Emissions Are Reduced or Sinks Are Enhanced Examples
					Examples

Change in Uses of Land
					Increasing carbon storage by using land differently or maintaining carbon storage by avoiding land degradation.

Encouraging the transformation of cropland to forest.

Avoiding the conversion of forest land to settlements.

Changes in Land Management Practices
					Improving management practices on existing land-use types.

Reducing soil erosion to minimize losses in soil carbon storage.

Planting after natural or human-induced forest disturbances to accelerate vegetation growth and minimize soil carbon losses.

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6,870 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 GWPs. Exit

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Greenhouse Gas Emissions

Overview of Greenhouse Gases

Overview

Carbon Dioxide

Methane

Nitrous Oxide

Fluorinated Gases

<img alt="Pie chart that shows different types of gases. 80.9 percent is from carbon dioxide fossil fuel use, deforestation, decay of biomass, etc.  10.6 percent is from methane. 5.9 percent is from nitrous oxide and 2.6 percent is from fluorinated gases." title="Pie chart that shows different types of gases. 80.9 percent is from carbon dioxide fossil fuel use, deforestation, decay of biomass, etc.  10.6 percent is from methane. 5.9 percent is from nitrous oxide and 2.6 percent is from fluorinated gases." height="384" width="381" class="right media-element file-full" typeof="foaf:Image" src="/sites/production/files/styles/large/public/2016-05/ghge-gases-overview_0.png" />Total Emissions in 2014 = 6,870 Million Metric Tons of CO2 equivalent.

Larger image to save or print.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 science of climate change and other climate forcers, such as black carbon, please visit Climate Change Science.

6,870 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.

The GWP values appearing in the Emissions webpages reflect the values used in the U.S. Inventory, which are drawn from the IPCC’s Fourth Assessment Report (AR4). For further discussion of GWPs and an estimate of GHG emissions using updated GWPs, see Annex 6 of the U.S. Inventory and the IPCC's discussion on GWPs. Exit

Carbon dioxide (CO2): Carbon dioxide enters the atmosphere through burning fossil fuels (coal, natural gas, and oil), solid waste, trees and wood products, and also as a result of certain chemical reactions (e.g., manufacture of cement). Carbon dioxide is removed from the atmosphere (or "sequestered") when it is absorbed by plants as part of the biological carbon cycle.

Methane (CH4): Methane is emitted during the production and transport of coal, natural gas, and oil. Methane emissions also result from livestock and other agricultural practices and by the decay of organic waste in municipal solid waste landfills.

Nitrous oxide (N2O): Nitrous oxide is emitted during agricultural and industrial activities, as well as during combustion of fossil fuels and solid waste.

Fluorinated gases: Hydrofluorocarbons, perfluorocarbons, sulfur hexafluoride, and nitrogen trifluoride are synthetic, powerful greenhouse gases that are emitted from a variety of industrial processes. Fluorinated gases are sometimes used as substitutes for stratospheric ozone-depleting substances (e.g., chlorofluorocarbons, hydrochlorofluorocarbons, and halons). These gases are typically emitted in smaller quantities, but because they are potent greenhouse gases, they are sometimes referred to as High Global Warming Potential gases ("High GWP gases").

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

How much of these gases are 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 Causes of Climate Change and the Climate Change Indicators: Atmospheric Concentrations of Greenhouse Gases pages.

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 global temperatures?

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) has been calculated to reflect how long it remains in the atmosphere, on average, and how strongly it absorbs energy. Gases with a higher GWP absorb more energy, per pound, than gases with a lower GWP, and thus contribute more to warming Earth.

Note: All emission estimates are from the  Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2014.

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Carbon Dioxide Emissions

Properties of Carbon Dioxide

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

Carbon dioxide (CO2) is the primary greenhouse gas emitted through human activities. In 2014, CO2 accounted for about 80.9% 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, to remove 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.1

<img alt="CO2 emissions by use. 37 percent is electricity, 31 percent is transportation, 15 percent is industry, 10 percent is residential and commercial, and 6 percent is other (non-fossil fuel combustion)." title="Pie chart that shows emissions by use. 37 percent is electricity, 31 percent is transportation, 15 percent is industry, 10 percent is residential and commercial, and 6 percent is other (non-fossil fuel combustion)." height="543" width="563" class="right media-element file-full" typeof="foaf:Image" src="/sites/production/files/styles/large/public/2016-05/ghge-gases-co2_1.png" />Note: All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2014.

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

Electricity. Electricity is a significant source of energy in the United States and is used to power homes, business, and industry. The combustion of fossil fuels to generate electricity is the largest single source of CO2 emissions in the nation, accounting for about 37 percent of total U.S. CO2 emissions and 30 percent of total U.S. greenhouse gas emissions in 2014. The type of fossil fuel used to generate electricity will emit different amounts of CO2. To produce a given amount of electricity, burning coal will produce more CO2 than oil or natural gas.

Transportation. The combustion of fossil fuels such as gasoline and diesel to transport people and goods is the second largest source of CO2 emissions, accounting for about 31 percent of total U.S. CO2 emissions and 25 percent of total U.S. greenhouse gas emissions in 2014. This category includes transportation sources such as highway vehicles, air travel, marine transportation, and rail.

Industry. Many industrial processes emit CO2 through fossil fuel combustion. Several processes also produce CO2 emissions through chemical reactions that do not involve combustion; for example, the production and consumption of mineral products such as cement, the production of metals such as iron and steel, and the production of chemicals. Fossil fuel combustion from various industrial processes accounted for about 15 percent of total U.S. CO2 emissions and 12 percent of total U.S. greenhouse gas emissions in 2014. Note that many industrial processes also use electricity and therefore indirectly cause the emissions from the electricity production.

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. However, emissions and removal of CO2 by these natural processes tend to balance. 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, since 1990, the management of forests and non-agricultural land 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 sink offset about 11 percent of total emissions in 2014 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 warming the atmosphere and its sources, visit the Causes of Climate Change page and the Climate Change Indicators page in the Science section.

Emissions and Trends

Carbon dioxide (CO2) emissions in the United States increased by about 9 percent between 1990 and 2014. 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. Between 1990 and 2014, the increase in CO2 emissions corresponded with increased energy use by an expanding economy and population, and an overall growth in emissions from electricity generation. Transportation emissions also contributed to the 9 percent increase, largely due to an increase in miles traveled by motor vehicles.

<img alt="Emissions started in 1990 at 5000 million metric tons (mmt), rose gradually to 6000 mmt in 2000, & remained there until 2008, when it began to decline and fluctuate. 2009: 5500, 2010: 5700, 2012: 5400, 2014: 5600 (all in mmt)." title="Emissions started in 1990 at 5000 million metric tons (mmt), rose gradually to 6000 mmt in 2000, & remained there until 2008, when it began to decline and fluctuate. 2009: 5500, 2010: 5700, 2012: 5400, 2014: 5600 (all in mmt)." height="488" width="928" class="center media-element file-full" typeof="foaf:Image" src="/sites/production/files/styles/large/public/2016-05/ghge-total-co2.png" />Note: All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2014.

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Reducing Carbon Dioxide Emissions

The most effective way to reduce carbon dioxide (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 from our nation's largest sources, including power plants and motor vehicles.

Learn about what EPA is doing to reduce carbon pollution from power plants.

Learn about EPA's motor vehicle standards.

Learn more about EPA's regulatory initiatives to reduce greenhouse gas emissions.

Examples of Reduction Opportunities for Carbon Dioxide

Strategy
					Examples of How Emissions Can be Reduced

Energy Efficiency

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

See EPA's ENERGY STAR® program for more information on energy-efficient appliances.

See EPA's and DOE's fueleconomy.gov site for more information on fuel-efficient vehicles.

Learn about EPA's motor vehicle standards that improve vehicle efficiency and save drivers money.

Energy Conservation

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.

Fuel Switching

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

Carbon Capture and Sequestration

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. Learn more.

* Carbon dioxide's lifetime is poorly defined 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 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.

References

1   NRC (2010). Advancing the Science of Climate Change. Exit National Research Council. The National Academies Press, Washington, DC, USA.

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Methane Emissions

Properties of Methane

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

Methane (CH4) is the second most prevalent greenhouse gas emitted in the United States from human activities. In 2014, CH4 accounted for about 11 percent of all U.S. greenhouse gas emissions from human activities. Methane is emitted by natural sources such as wetlands, as well as human activities such as leakage from natural gas systems and the raising of livestock. 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 on climate change is more than 25 times greater than CO2 over a 100-year period.

Globally, over 60 percent of total CH4 emissions come from human activities.1 Methane is emitted from industry, agriculture, and waste management activities, described below.

<img alt="US Methane Emissions by Source: U.S. methane emissions by source: 33% is from natural gas and petroleum systems, 22% is from enteric fermentation, 20% is from landfills, 9% is from coal mining, 8% is from manure management, and 6% is from other sources." title="US Methane Emissions by Source: U.S. methane emissions by source: 33% is from natural gas and petroleum systems, 22% is from enteric fermentation, 20% is from landfills, 9% is from coal mining, 8% is from manure management, and 6% is from other sources." height="321" width="369" class="right media-element file-full" typeof="foaf:Image" src="/sites/production/files/styles/large/public/2016-05/ghge-gases-ch4_0.png" />Note: All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2014.

Larger image to save or print.Industry. Natural gas and petroleum systems are the largest source of CH4 emissions from industry in the United States. Methane is the primary component of natural gas. Some CH4 is emitted to the atmosphere during the production, processing, storage, transmission, and distribution of natural gas. Because gas is often found alongside petroleum, the production, refinement, transportation, and storage of crude oil is also a source of CH4 emissions. For more information, see the Inventory of U.S. Greenhouse Gas Emissions and Sinks sections on Natural Gas Systems and Petroleum Systems.

Agriculture. Domestic livestock such as cattle, buffalo, sheep, goats, and camels produce large amounts of CH4 as part of their normal digestive process. Also, when animals' manure is stored or managed in lagoons or holding tanks, CH4 is produced. Because humans raise these animals for food, the emissions are considered human-related. Globally, the Agriculture sector is the primary source of CH4 emissions. For more information, see the Inventory of U.S. Greenhouse Gas Emissions and Sinks Agriculture chapter.

Waste from Homes and Businesses. Methane is generated in landfills as waste decomposes and in the treatment of wastewater. Landfills are the third largest source of CH4 emissions in the United States. For more information see the U.S. Inventory's Waste chapter.

Methane is also emitted from a number of natural sources. 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 Causes of Climate Change page and the Climate Change Indicators page in the Science section.

Emissions and Trends

Methane (CH4) emissions in the United States decreased by 6 percent between 1990 and 2014. During this time period, emissions increased from sources associated with agricultural activities, while emissions decreased from sources associated with the exploration and production of natural gas and petroleum products.

<img alt="U.S. methane emissions: Emissions hover between 700-800 million metric tons of CO2 equivalents from 1990-2014. 1990-1996: ~780. Declines to ~700 in 2004, inclines to ~740 in 2008, declines to ~715 in 2012, and inclines to ~730 mmtCO2e in 2013-2014." title="U.S. methane emissions: Emissions hover between 700-800 million metric tons of CO2 equivalents from 1990-2014. 1990-1996: ~780. Declines to ~700 in 2004, inclines to ~740 in 2008, declines to ~715 in 2012, and inclines to ~730 mmtCO2e in 2013-2014." height="547" width="928" class="center media-element file-full" typeof="foaf:Image" src="/sites/production/files/styles/large/public/2016-05/ghge-total-ch4.png" />Note: All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2014. These estimates use a global warming potential for methane of 25, based on reporting requirements under the United Nations Framework Convention on Climate Change.

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Reducing Methane Emissions

There are a number of ways to reduce methane (CH4) emissions. Some examples are discussed below. EPA has a series of voluntary programs for reducing CH4 emissions, and is supporting the president's Strategy to Reduce Methane Emissions(15 pp, 1.9 M, About PDF). EPA also supports the Global Methane Initiative Exit, an international partnership encouraging global methane reduction strategies.

Examples of Reduction Opportunities for Methane

Emissions Source
					How Emissions Can be Reduced

Industry

Upgrading the equipment used to produce, store, and transport oil and 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.

Agriculture

Methane can be reduced and captured by altering manure management strategies at livestock operations or animal feeding practices. Learn more about these strategies and EPA's AgSTAR Program.

Waste from Homes and Businesses

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 EPA (2010). Methane and Nitrous Oxide Emissions from Natural Sources. U.S. Environmental Protection Agency, Washington, DC, USA.

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Nitrous Oxide Emissions

Properties of Nitrous Oxide

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

In 2014, nitrous oxide (N2O) accounted for about 6 percent of all U.S. greenhouse gas emissions from human activities. Nitrous oxide is naturally present in the atmosphere as part of the Earth's nitrogen cycle, and has a variety of natural sources. However, human activities such as agriculture, fossil fuel combustion, wastewater management, and industrial processes are increasing the amount of N2O in the atmosphere. 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.

Globally, about 40 percent of total N2O emissions come from human activities.1 Nitrous oxide is emitted from agriculture, transportation, and industry activities, described below.

<img alt="U.S. nitrous oxide emissions by source: 79% is from agricultural soil management, 6% from stationary combustion, 5% from industry or chemical production, 4% from manure management, 4% from transportation, and 2% from other sources." title="U.S. nitrous oxide emissions by source: 79% is from agricultural soil management, 6% from stationary combustion, 5% from industry or chemical production, 4% from manure management, 4% from transportation, and 2% from other sources." height="399" width="448" class="right media-element file-medium right" typeof="foaf:Image" src="/sites/production/files/styles/medium/public/2016-05/ghge-gases-n2o_2.png" />Note: All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2014.

Larger image to save or print.Agriculture. Nitrous oxide is emitted when people add nitrogen to the soil through the use of synthetic fertilizers. Agricultural soil management is the largest source of N2O emissions in the United States, accounting for about 79 percent of total U.S. N2O emissions in 2014. Nitrous oxide is also emitted during the breakdown of nitrogen in livestock manure and urine, which contributed to 4 percent of N2O emissions in 2014.

Transportation. Nitrous oxide is emitted when transportation fuels are burned. Motor vehicles, including passenger cars and trucks, are the primary source of N2O emissions from transportation. The amount of N2O emitted from transportation depends on the type of fuel and vehicle technology, maintenance, and operating practices.

Industry. Nitrous oxide is generated as a byproduct during the production of nitric acid, which is used to make synthetic commercial fertilizer, and in the production of adipic acid, which is used to make fibers, like nylon, and other synthetic products.

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 role of N2O in warming the atmosphere and its sources, visit the Causes of Climate Change page and the Climate Change Indicators page in the Science section.

Emissions and Trends

Nitrous oxide (N2O) emissions in the United States have decreased by 1 percent between 1990 and 2014. This decrease in emissions is due in part to a decrease in emissions from mobile combustion resulting from emission control standards for on-road vehicles. Nitrous oxide emissions from agricultural soils have varied during this period and were about 5 percent higher in 2014 than in 1990.

Going forward, N2O emissions are projected to increase by 5 percent between 2005 and 2020, driven largely by increases in emissions from agricultural activities.2

<img alt="U.S. nitrous oxide emissions: 1990 emissions were ~400 million metric tons of CO2 equivalents (mmtCO2e). The emissions peak in 1998 around 430 mmtCO2e, then decrease to just above 400 mmtCO2e in 2014." title="U.S. nitrous oxide emissions: 1990 emissions were ~400 million metric tons of CO2 equivalents (mmtCO2e). The emissions peak in 1998 around 430 mmtCO2e, then decrease to just above 400 mmtCO2e in 2014." height="542" width="928" class="center media-element file-full" typeof="foaf:Image" src="/sites/production/files/styles/large/public/2016-05/ghge-total-n2o.png" />Note: All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2014.

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Reducing Nitrous Oxide Emissions

There are a number of ways to reduce emissions of nitrous oxide (N2O), discussed below.

Examples of Reduction Opportunities for Nitrous Oxide Emissions

Emissions Source
					Examples of How Emissions Can be Reduced

Agriculture

The application of fertilizers accounts for the majority of N2O emissions. Emissions can be reduced by reducing nitrogen-based fertilizer applications and applying fertilizers more efficiently,3 as well as following better manure management practices.

Transportation

Nitrous oxide is a byproduct of fuel combustion, so reducing mobile fuel consumption in motor vehicles can reduce transportation emissions.

Additionally, the introduction of pollution control technologies, such as catalytic converters to reduce exhaust pollutants from passenger cars, can also reduce emissions of N2O.

Industry

Nitrous oxide is generally emitted from industry through fossil fuel combustion, so technological upgrades and fuel switching are effective ways to reduce industry emissions of N2O.

Production of adipic acid results in N2O emissions that can be reduced through technological upgrades.

References

1  EPA (2010). Methane and Nitrous Oxide Emissions from Natural Sources. U.S. Environmental Protection Agency, Washington, DC, USA.
2  U.S. Department of State (2010). Fifth Climate Action Report to the UN Framework Convention on Climate Change: Projected Greenhouse Gas Emissions(10 pp, 577 K, About PDF). U.S. Department of State, Washington, DC, USA.
3  <a href="http://nepis.epa.gov/Exe/ZyNET.exe/P100GO8M.TXT?ZyActionD=ZyDocument&Client=EPA&Index=2000+Thru+2005&Docs=&Query=&Time=&EndTime=&SearchMethod=1&TocRestrict=n&Toc=&TocEntry=&QField=&QFieldYear=&QFieldMonth=&QFieldDay=&IntQFieldOp=0&ExtQFieldOp=0&XmlQuery=&File=D%3A%5Czyfiles%5CIndex%20Data%5C00thru05%5CTxt%5C00000032%5CP100GO8M.txt&User=ANONYMOUS&Password=anonymous&SortMethod=h%7C-&MaximumDocuments=1&FuzzyDegree=0&ImageQuality=r75g8/r75g8/x150y150g16/i425&Display=p%7Cf&DefSeekPage=x&SearchBack=ZyActionL&Back=ZyActionS&BackDesc=Results%20page&MaximumPages=1&ZyEntry=1&SeekPage=x&ZyPURL">EPA (2005). Greenhouse Gas Mitigation Potential in U.S. Forestry and Agriculture. U.S. Environmental Protection Agency, Washington, DC, USA.

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Emissions of Fluorinated Gases

Properties of F-gases

Chemical Formula:

					HFCs, PFCs, NF3, SF6
Lifetime in Atmosphere:

					HFCs: 1–270 years

					PFCs: 2,600–50,000 years

					NF3: 740 years

					SF6: 3,200 years
Global Warming Potential (100-year):

					HFCs: 12–14,800

					PFCs: 7,390–12,200

					NF3: 17,200

					SF6: 22,800

Unlike many other greenhouse gases, fluorinated gases have no natural sources and only come from human-related activities. They are emitted 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 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, fluorinated gases are well-mixed in the atmosphere, spreading around the world after they are emitted. 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.

<img alt="U.S. fluorinated gas emissions by source: 90% from the substitution of ozone depleting substances, 3% electrical transmission & distribution, 3% HCFC-22 production, 3% semiconductor manufacture, & 2% production & processing of aluminum & magnesium." title="U.S. fluorinated gas emissions by source: 90% from the substitution of ozone depleting substances, 3% electrical transmission & distribution, 3% HCFC-22 production, 3% semiconductor manufacture, & 2% production & processing of aluminum & magnesium." height="436" width="448" class="right media-element file-medium right" typeof="foaf:Image" src="/sites/production/files/styles/medium/public/2016-05/ghge-gases-fgas_2.png" />Note: All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2014.

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Substitution for Ozone-Depleting Substances. Hydrofluorocarbons are used as refrigerants, aerosol propellants, solvents, and fire retardants. The major emissions source of these compounds is their use as refrigerants—for example, in air conditioning systems in both vehicles and buildings. These chemicals were developed as a replacement for chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) because they do not deplete the stratospheric ozone layer. Chlorofluorocarbons and HCFCs are being phased out under an international agreement, called the Montreal Protocol. Unfortunately, HFCs are potent greenhouse gases with long atmospheric lifetimes and high GWPs, and they are released into the atmosphere through leaks, servicing, and disposal of equipment in which they are used.

Industry. Perfluorocarbons are compounds produced as a byproduct of various industrial processes associated with aluminum production and the manufacturing of semiconductors. Like HFCs, PFCs generally have long atmospheric lifetimes and high GWPs. Sulfur hexafluoride is used in magnesium processing and semiconductor manufacturing, as well as a tracer gas for leak detection. HFC-23 is produced as a byproduct of HCFC-22 production.

Transmission and Distribution of Electricity. Sulfur hexafluoride is used in electrical transmission equipment, including circuit breakers. The GWP of SF6 is 22,800, making it the most potent greenhouse gas that the Intergovernmental Panel on Climate Change has evaluated.

To find out more about the role of fluorinated gases in warming the atmosphere, and their sources, visit the Causes of Climate Change page and the Climate Change Indicators page in the Science section.

Emissions and Trends

Overall, fluorinated gas emissions in the United States have increased by about 77 percent between 1990 and 2014. This increase has been driven by a 258 percent 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 electricity transmission and distribution industry (SF6).

Going forward, HFC emissions are projected to grow by nearly 141 percent between 2005 and 2020 as demands for refrigeration continue to grow and as more ozone-depleting substances are replaced. During this same period, emissions of SF6 are expected to decline by over 25 percent, while emissions of PFCs are projected to remain flat. Since the emissions from HFCs are far greater than the emissions of the other gases on a carbon dioxide-equivalence basis, substantial growth in emissions of fluorinated gases is expected to continue.1

<img alt="U.S. fluorinated gas emissions, 1990-2014: Emissions have increased from ~100 million metric tons of CO2 equivalents in 1990 to just above 180 in 2014. It should be noted that there is a slight decline from 1998-2003, but the overall trend is an increase." title="U.S. fluorinated gas emissions, 1990-2014: Emissions have increased from ~100 million metric tons of CO2 equivalents in 1990 to just above 180 in 2014. It should be noted that there is a slight decline from 1998-2003, but the overall trend is an increase." height="636" width="928" class="center media-element file-full" typeof="foaf:Image" src="/sites/production/files/styles/large/public/2016-05/ghge-total-fgas.png" />Note: All emission estimates from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2014.

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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. However, there are a number of ways to reduce emissions of fluorinated gases, described below.

Examples of Reduction Opportunities for Fluorinated Gases

Emissions Source
					Examples of How Emissions Can be Reduced

Substitution of Ozone-Depleting Substances in Homes and Businesses

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

Industry

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. The following are EPA programs working to reduce these gases in the Industry sector:

Voluntary Aluminum Industrial Partnership

The SF6 Emission Reduction Partnership for the Magnesium Industry

The PFC Reduction/Climate Partnership for the Semiconductor Industry

Electricity Transmission and Distribution

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 employee training.

Transportation

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. One important way the EPA is working to reduce HFC emissions is through its light-duty and heavy-duty vehicle standards.

References

1  U.S. Department of State (2010). Fifth Climate Action Report to the UN Framework Convention on Climate Change: Projected Greenhouse Gas Emissions(10 pp, 577 K, About PDF). U.S. Department of State, Washington, DC, USA.

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Greenhouse Gas Emissions

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