Climate Change Indicators in the United States: U.S. Greenhouse Gas Emissions
www.epa.gov/climatechange/indicators - Updated June 2015
U.S. Greenhouse Gas Emissions
This indicator describes emissions of greenhouse gases in the United States.
Background
A number of factors influence the quantities of greenhouse gases released into the atmosphere,
including economic activity, population, consumption patterns, energy prices, land use, and technology.
There are several ways to track these emissions, such as by measuring emissions directly, calculating
emissions based on the amount of fuel that people burn, and estimating other activities and their
associated emissions. EPA has two key programs that provide data on greenhouse gas emissions in the
United States: the Inventory of U.S. Greenhouse Gas Emissions and Sinks and the Greenhouse Gas
Reporting Program.
About the Indicator
This indicator focuses on emissions of carbon dioxide, methane, nitrous oxide, and several fluorinated
gases—all important greenhouse gases that are influenced by human activities. These particular gases
are covered under the United Nations Framework Convention on Climate Change, an international
agreement that requires participating countries to develop and periodically submit an inventory of
greenhouse gas emissions. Data and analysis for this indicator come from EPA's annual inventory
submission, the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2013.1 This indicator is
restricted to emissions associated with human activities.
Each greenhouse gas has a different lifetime (how long it stays in the atmosphere) and a different ability
to trap heat in our atmosphere. To allow different gases to be compared and added together, emissions
are converted into carbon dioxide equivalents. This step uses each gas's 100-year global warming
potential, which measures how much a given amount of the gas is estimated to contribute to global
warming over a period of 100 years after being emitted. Carbon dioxide is assigned a global warming
potential equal to 1. This analysis uses global warming potentials from the Intergovernmental Panel on
Climate Change's (IPCC's) Fourth Assessment Report. In that report, methane has a global warming
potential of 25, which means a ton of methane emissions contributes 25 times as much warming as a
ton of carbon dioxide emissions over 100 years, and that ton of methane emissions is therefore equal to
25 tons of carbon dioxide equivalents. See the table in the Web version of this indicator for comparison
with global warming potentials from IPCC's Fifth Assessment Report. For additional perspective, this
indicator also shows greenhouse gas emissions in relation to economic output and population.
• In 2013, U.S. greenhouse gas emissions totaled 6,673 million metric tons (14.7 trillion pounds) of
carbon dioxide equivalents. This 2013 total represents a 6 percent increase since 1990 but a 9
percent decrease since 2005 (see Figure 1).
Key Points
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Climate Change Indicators in the United States: U.S. Greenhouse Gas Emissions
www.epa.gov/climatechange/indicators - Updated June 2015
• For the United States, during the period from 1990 to 2013 (see Figure 1):
o Emissions of carbon dioxide, the primary greenhouse gas emitted by human activities,
increased by 7 percent.
o Methane emissions decreased by 15 percent, as reduced emissions from landfills, coal
mines, and natural gas systems were greater than increases in emissions from activities
such as livestock production.2
o Nitrous oxide emissions, predominantly from agricultural soil management practices
such as the use of nitrogen as a fertilizer, increased by nearly 8 percent.
o Emissions of fluorinated gases (hydrofluorocarbons, perfluorocarbons, sulfur
hexafluoride, and nitrogen trifluoride), released as a result of commercial, industrial,
and household uses, increased by 73 percent.
• Among the various sectors of the U.S. economy, electricity generation (power plants) accounts
for the largest share of emissions—32 percent of total greenhouse gas emissions since 1990.
Transportation is the second-largest sector, accounting for 26 percent of emissions since 1990
(see Figure 2).
• Emissions sinks, the opposite of emissions sources, absorb carbon dioxide from the atmosphere.
In 2013, 13 percent of U.S. greenhouse gas emissions were offset by sinks resulting from land
use and forestry practices (see Figure 2). One major sink is the net growth of forests, which
remove carbon from the atmosphere. Other carbon sinks are associated with how people use
the land, including the practice of depositing yard trimmings and food scraps in landfills.
• Emissions increased at about the same rate as the population from 1990 to 2007, which caused
emissions per capita to remain fairly level (see Figure 3). Total emissions and emissions per
capita declined from 2007 to 2009, due in part to a drop in U.S. economic production during this
time. Emissions decreased again from 2010 to 2012, largely due to the growing use of natural
gas to generate electricity in place of more carbon-intensive fuels.3
• From 1990 to 2013, greenhouse gas emissions per dollar of goods and services produced by the
U.S. economy (the gross domestic product or GDP) declined by 40 percent (see Figure 3). This
change may reflect a combination of increased energy efficiency and structural changes in the
economy.
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Climate Change Indicators in the United States: U.S. Greenhouse Gas Emissions
www.epa.gov/climatechange/indicators - Updated June 2015
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Figure 1. U.S. Greenhouse Gas Emissions by Gas, 1990-2013
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Carbon dioxide
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1990 1992 1 994 1996 1998 2000 2002 2004 2006 2008 2010 2012
Year
This figure shows emissions of carbon dioxide, methane, nitrous oxide, and several fluorinated gases in
the United States from 1990 to 2013. For consistency, emissions are expressed in million metric tons of
carbon dioxide equivalents.
* HFCs are hydrofluorocarbons, PFCs are perfluorocarbons, SF6 is sulfur hexafluoride, and NF3 is nitrogen
trifluoride.
Data source: U.S. EPA, 20154
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Climate Change Indicators in the United States: U.S. Greenhouse Gas Emissions
www.epa.gov/climatechange/indicators - Updated June 2015
Figure 2. U.S. Greenhouse Gas Emissions and Sinks by Economic Sector,
1990-2013
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Climate Change Indicators in the United States: U.S. Greenhouse Gas Emissions
www.epa.gov/climatechange/indicators - Updated June 2015
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Figure 3. U.S. Greenhouse Gas Emissions per Capita and per Dollar of GDP,
1990-2013
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1990 1992 1994 1996 1993 2000 2002 2004 2006 2008 2010 2012
Year
This figure shows trends in greenhouse gas emissions from 1990 to 2013 per capita (heavy orange line),
based on the total U.S. population (thin orange line). It also shows trends in emissions per dollar of real
GDP (heavy blue line). Real GDP (thin blue line) is the value of all goods and services produced in the
country during a given year, adjusted for inflation. All data are indexed to 1990 as the base year, which is
assigned a value of 100. For instance, a real GDP value of 175 in the year 2013 would represent a 75
percent increase since 1990.
Data source: U.S. EPA, 2015s
Indicator Notes
While this indicator includes the major greenhouse gases emitted by human activities, it does not
include other greenhouse gases and substances that are not covered under the United Nations
Framework Convention on Climate Change but that still affect the Earth's energy balance and climate
(see the Climate Forcing indicator for more details). For example, this indicator excludes ozone-
depleting substances such as chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), which
have high global warming potentials, as these gases have been or are currently being phased out under
an international agreement called the Montreal Protocol. This indicator also excludes black carbon and
aerosols, which most greenhouse gas emissions inventories do not cover. There are also many natural
greenhouse gas emissions sources; however, this indicator includes only emissions that are associated
with human activities—those that are most responsible for the observed buildup of these gases in our
atmosphere.
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Climate Change Indicators in the United States: U.S. Greenhouse Gas Emissions
www.epa.gov/climatechange/indicators - Updated June 2015
Data Sources
Data for this indicator came from EPA's Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-
2013. This report is available online
at: www.epa.gov/climatechange/ghgemissions/usinventorvreport.html. The calculations in Figure 3 are
based on GDP and population data provided by the U.S. Bureau of Economic Analysis and the U.S.
Census, respectively.
1 U.S. EPA (U.S. Environmental Protection Agency). 2015. Inventory of U.S. greenhouse gas emissions and sinks:
1990-2013. EPA430-R-15-004. www.epa.gov/climatechange/ghgemissions/usinventorvreport.html.
2 U.S. EPA (U.S. Environmental Protection Agency). 2015. Inventory of U.S. greenhouse gas emissions and sinks:
1990-2013. EPA430-R-15-004. www.epa.gov/climatechange/ghgemissions/usinventorvreport.html.
3 U.S. EPA (U.S. Environmental Protection Agency). 2015. Inventory of U.S. greenhouse gas emissions and sinks:
1990-2013. EPA430-R-15-004. www.epa.gov/climatechange/ghgemissions/usinventorvreport.html.
4 U.S. EPA (U.S. Environmental Protection Agency). 2015. Inventory of U.S. greenhouse gas emissions and sinks:
1990-2013. EPA430-R-15-004. www.epa.gov/climatechange/ghgemissions/usinventorvreport.html.
5 U.S. EPA (U.S. Environmental Protection Agency). 2015. Inventory of U.S. greenhouse gas emissions and sinks:
1990-2013. EPA430-R-15-004. www.epa.gov/climatechange/ghgemissions/usinventorvreport.html.
6 U.S. EPA (U.S. Environmental Protection Agency). 2015. Inventory of U.S. greenhouse gas emissions and sinks:
1990-2013. EPA430-R-15-004. www.epa.gov/climatechange/ghgemissions/usinventorvreport.html.
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