U.S. Greenhouse Gas Inventory

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EPA

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 2008 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) (28 pp, 482K, 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, 430K, About PDF). The 2009 Inventory of U.S. Greenhouse Gas Emissions and Sinks is now available.

Figure 1: U.S. Greenhouse Gas Emissions by Gas. Illustrates U.S. greenhouse gas emissions by gas, in cumulative CO2 equivalents, from 1990 through 2005. There is generally an upward trend, starting from 6,242 Tg CO2 Eq. in 1990 and ending with 7,260 Tg CO2 Eq. in 2005. The three exceptions to this trend are 1991, where emissions were 6,186 Tg CO2 Eq, down from 6,242 Tg CO2 Eq. in 1990; 2001, where emissions were 7,027 Tg CO2 Eq., down from 7,147 Tg CO2 Eq. in 2000; and 2006, where emissions were 7,054, down from 7,130 in 2005.

Reference: Inventory of U.S. Greenhouse Gas Emissions and Sinks:
1990-2006, USEPA #430-R-08-005

The figure above illustrates the relative contribution of the direct greenhouse gases to total U.S. emissions for the period 1990-2006. The primary greenhouse gas emitted by human activities in the United States was carbon dioxide (CO2), representing approximately 85 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 2006. 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.

Emissions Allocated to Economic Sectors. This figure illustrates the data presented in Table ES-7, U.S. greenhouse gas emissions allocated to economic sectors from 1990 through 2006. Emissions from the industrial economic sector are gradually declining, while emissions from the other economic sectors are steady or rising over the timeseries.

Reference: Inventory of U.S. Greenhouse Gas Emissions and Sinks:
1990-2006, USEPA #430-R-08-005

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.

Figure 3: Emissions with Electricity Distributed to Economic Sectors. This figure illustrates the data presented in Table ES-8, U.S Greenhouse Gas Emissions by 'Economic Sector' and Gas with Electricity-Related Emissions Distributed (Tg CO2 Eq.).

Reference: Inventory of U.S. Greenhouse Gas Emissions and Sinks:
1990-2006, USEPA #430-R-08-005

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 2006 removed approximately 13 percent of total U.S. emissions.

Figure 4: Estimates of Net Annual Changes in Carbon Stocks for Major Carbon Pools. This figure is a line graph indicating forest carbon flux for the years 1990 through 2005. Total net carbon flux combines forest soils, harvested wood, and trees, with trees representing the primary contributor to total net carbon flux. The net carbon flux for each element is negative across all years in the timeseries. Total net carbon flux decreased from -169.6 Tg in 1990 to -203.2 Tg in 2005.

Reference: Inventory of U.S. Greenhouse Gas Emissions and Sinks:
1990-2006, USEPA #430-R-08-005

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