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U.S. Greenhouse Gas Inventory
EPA develops the national greenhouse gas inventory each year to track
the national trend in emissions and removals since 1990. The national greenhouse
gas inventory is submitted to the United Nations in accordance with the
Framework Convention on Climate Change 
. 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.
Please see the 2007 Inventory of U.S. Greenhouse Gas Emissions and Sinks for a detailed analysis of all U.S. emissions and removals. You may also download the Executive Summary (PDF) (26 pp, 27K, About PDF), which includes an overview of recent trends, anthropogenic sources and sinks of greenhouse gases and an explanation of the relative importance of emissions and removals from each source category. In addition, a one page tabular summary of emissions by source is provided in the Fast Facts card (PDF) (2 pp, 219K, About PDF).
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| Reference: Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2005, USEPA #430-R-07-002 |
The figure above illustrates the relative contribution of the direct greenhouse gases to total U.S. emissions for the period 1990-2005. The primary greenhouse gas emitted by human activities in the United States was carbon dioxide (CO2), representing approximately 84 percent of total greenhouse gas emissions. The largest source of CO2 was from the combustion of fossil fuels. Methane emissions, which have steadily declined since 1990, resulted primarily from decomposition of wastes in landfills, natural gas systems and activities associated with domestic livestock. Agricultural soil management and mobile source fossil fuel combustion were the major sources of nitrous oxide emissions. The emissions of hydrofluorocarbons, which are substitutes for ozone depleting substances, were the primary component of fluorinated gas emissions.
To compare and combine emissions of different greenhouse gases into a national total, EPA uses global warming potentials (GWPs). GWPs compare the radiative forcing or ability to trap heat of one metric ton of a greenhouse gas to a metric ton of CO2.
The U.S. greenhouse gas inventory also presents emissions by more commonly used economic categories: agriculture, commercial, electricity generation, industry, residential and transportation. Using this categorization, emissions from electricity generation accounted for the largest portion of U.S. greenhouse gas emissions in 2005. Transportation activities accounted for the second largest portion and emissions from industry comprised the third largest portion. The agriculture, commercial and residential economic sectors, listed in descending order of their contribution, together account for the remaining U.S. greenhouse gas emissions.
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| Reference: Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2005, USEPA #430-R-07-002 |
Electricity, though produced at power plants, is ultimately consumed in the other economic sectors. When emissions from electricity are distributed among these sectors, the industrial sector accounts for the largest share of U.S. greenhouse gas emissions. Transportation remains the second largest contributor to emissions. Emissions from the residential and commercial sectors increase substantially due to their relatively large share of electricity consumption (e.g., lighting, appliances, etc.), with agriculture consuming little electricity.
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| Reference: Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2005, USEPA #430-R-07-002 |
Carbon dioxide can be removed from the atmosphere through activities such as planting trees, improving existing forests and soil management. As shown below, total carbon sequestration in the U.S. in 2005 removed approximately 11 percent of total U.S. emissions.
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| Reference: Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2005, USEPA #430-R-07-002 |