Climate Change Indicators in the United States U.S. Greenhouse Gas Emissions Updated May 2014

Climate Change Indicators in the United States: U.S. Greenhouse Gas Emissions
www.epa.gov/climatechange/indicators - Updated May 2014

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: 1990-2012.1 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) Second Assessment Report. In that report, methane has a global warming
potential of 21, which means a ton of methane emissions contributes 21 times as much warming as a
ton of carbon dioxide emissions over 100 years, and that ton of methane emissions is therefore equal to
21 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 2012, U.S. greenhouse gas emissions totaled 6,526 million metric tons (14.4 trillion pounds) of
carbon dioxide equivalents. This 2012 total represents a 5 percent increase since 1990 but a 10
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 May 2014

• For the United States, during the period from 1990 to 2012 (see Figure 1):

o Emissions of carbon dioxide, the primary greenhouse gas emitted by human activities,
increased by 5 percent.

o Methane emissions decreased by 11 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 3 percent.

o Emissions of fluorinated gases (hydrofluorocarbons, perfluorocarbons, and sulfur
hexafluoride), released as a result of commercial, industrial, and household uses,
increased by 83 percent.

• Electricity generation is the largest U.S. emissions source, accounting for 32 percent of total
greenhouse gas emissions since 1990. Transportation is the second-largest source of
greenhouse gas emissions, accounting for 27 percent of emissions since 1990 (see Figure 2).

• Emissions sinks, the opposite of emissions sources, absorb carbon dioxide from the atmosphere.
In 2012, 15 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 2012, greenhouse gas emissions per dollar of goods and services produced by the
U.S. economy (the gross domestic product or GDP) declined by 39 percent (see Figure 3). This
change may reflect a combination of increased energy efficiency and structural changes in the
economy.

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d%	Climate Change Indicators in the United States: U.S. Greenhouse Gas Emissions

www.epa.gov/climatechange/indicators - Updated May 2014

Figure 1. U.S. Greenhouse Gas Emissions by Gas, 1990-2012

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Carbon dioxide

1990 1992 1994 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 2012. For consistency, emissions are expressed in million metric tons of
carbon dioxide equivalents.

* HFCs are hydrofluorocarbons, PFCs are perfluorocarbons, and SF6 is sulfur hexafluoride.

Data source: U.S. EPA, 20144

3

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Climate Change Indicators in the United States: U.S. Greenhouse Gas Emissions

www.epa.gov/climatechange/indicators - Updated May 2014

Figure 2. U.S. Greenhouse Gas Emissions and Sinks by Economic Sector,
1990-2012

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Land use, land-use change, and forestry (shks)

1990 1992 1994 1996 1998 2000 2002 2004 2006 2003 2010 2012

Year

This figure shows greenhouse gas emissions and sinks (negative values) by source in the United States
from 1990 to 2012. For consistency, emissions are expressed in million metric tons of carbon dioxide
equivalents. All electric power emissions are grouped together in the "Electricity generation" sector, so
other sectors such as "Residential" and "Commercial" are only showing non-electric sources, such as
burning oil or gas for heating. Totals do not match Figure 1 exactly because the economic sectors shown
here do not include emissions from U.S. territories outside the 50 states.

Data source: U.S. EPA, 2014s

4

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d% Climate Change Indicators in the United States: U.S. Greenhouse Gas Emissions

www.epa.gov/climatechange/indicators - Updated May 2014

Figure 3. U.S. Greenhouse Gas Emissions per Capita and per Dollar of GDP,
1990-2012

Population

1990 1992 1994 1996 1998 2000 2002 2 004 2006 2008 2010 2012

Year

Emissions
perSGDP

Emissions
per capita

1990= 101

This figure shows trends in greenhouse gas emissions from 1990 to 2012 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 173 in the year 2012 would represent a 73
percent increase since 1990.

Data source: U.S. EPA, 2014s

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 May 2014

Data Sources

Data for this indicator came from EPA's Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-
2012. This report is available online at:

www.epa.gov/climatechange/ghgemissions/usinventoryreport.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). 2014. Inventory of U.S. greenhouse gas emissions and sinks:
1990-2012. EPA 430-R-14-003. www.epa.gov/climatechange/ghgemissions/usinventorvreport.html.

2 U.S. EPA (U.S. Environmental Protection Agency). 2014. Inventory of U.S. greenhouse gas emissions and sinks:
1990-2012. EPA 430-R-14-003. www.epa.gov/climatechange/ghgemissions/usinventorvreport.html.

3 U.S. EPA (U.S. Environmental Protection Agency). 2014. Inventory of U.S. greenhouse gas emissions and sinks:
1990-2012. EPA 430-R-14-003. www.epa.gov/climatechange/ghgemissions/usinventorvreport.html.

4 U.S. EPA (U.S. Environmental Protection Agency). 2014. Inventory of U.S. greenhouse gas emissions and sinks:
1990-2012. EPA 430-R-14-003. www.epa.gov/climatechange/ghgemissions/usinventorvreport.html.

5 U.S. EPA (U.S. Environmental Protection Agency). 2014. Inventory of U.S. greenhouse gas emissions and sinks:
1990-2012. EPA 430-R-14-003. www.epa.gov/climatechange/ghgemissions/usinventorvreport.html.

6 U.S. EPA (U.S. Environmental Protection Agency). 2014. Inventory of U.S. greenhouse gas emissions and sinks:
1990-2012. EPA 430-R-14-003. www.epa.gov/climatechange/ghgemissions/usinventorvreport.html.

&EPA

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