Overview 

Figure Data

This report, in accordance with Section 1605(a) of the Energy Policy Act of 1992, provides estimates of U.S. emissions of greenhouse gases.¹ Table ES1 shows trends in emissions of the principal greenhouse gases, measured in million metric tons of native gas. Throughout the remainder of the report, emissions are given in carbon dioxide equivalents, which put the emissions of each gas in comparable terms of their global warming potentials (GWPs) relative to that of carbon dioxide.² As shown in Table ES2, U.S. emissions of greenhouse gases in 2005 totaled 7,147.2 million metric tons carbon dioxide equivalent (MMTCO₂e), 0.6 percent more than in 2004 (7,104.6 MMTCO₂e). The modest increase in total greenhouse gas emissions in 2005 is attributable mainly to below-average growth in emissions of carbon dioxide (0.3 percent). There were larger increases in emissions of nitrous oxide (1.9 percent) and methane (0.9 percent), but collectively these two gases make up only about 14 percent of total U.S. greenhouse gas emissions. Emissions of high-GWP gases—hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF₆) —increased by 7.2 percent, but their share of the total is only 2.2 percent. The U.S. economy grew by 3.2 percent in 2005. Consequently, U.S. greenhouse gas intensity (greenhouse gas emissions per unit of real economic output) was 2.5 percent lower in 2005 than in 2004. From 1990 to 2005, U.S. greenhouse gas intensity declined by 25 percent, or by an average of 1.9 percent per year. 

U.S. greenhouse gas emissions in 2005 were 17 percent higher than the 1990 emissions level of 6,112.8 MMTCO₂e—an average annual increase of 1.0 percent over the period. Since 1990, U.S. emissions have increased more slowly than the average annual growth in population (1.2 percent), primary energy consumption (1.1 percent), electric power generation (1.9 percent), or gross domestic product (3.0 percent). While the annual growth rate in carbon dioxide emissions since 1990 (1.2 percent) has closely tracked annual growth in population and energy consumption, the average annual rate of growth in total greenhouse gas emissions has been lower (1.0 percent) because of reductions in methane emissions and relatively slow annual growth in nitrous oxide emissions (0.6 percent) since 1990. 

During 2005, approximately 83 percent of total U.S. greenhouse gas emissions consisted of carbon dioxide from the combustion and nonfuel use of fossil fuels (Figure ES1), such as coal, petroleum, and natural gas (after adjustments for U.S. Territories and international bunker fuels). U.S. emissions trends are driven largely by trends in fossil energy consumption. In recent years, national energy consumption, like emissions, has grown relatively slowly, with year-to-year deviations from trend growth caused by weather-related phenomena, fluctuations in business cycles, changes in the fuel mix for electric power generation, and developments in domestic and international energy markets. 

Other 2005 U.S. greenhouse gas emissions include carbon dioxide from non-combustion sources (1.5 percent of total U.S. greenhouse gas emissions), methane (8.6 percent), nitrous oxide (5.1 percent), and other gases (2.2 percent). Methane and nitrous oxide emissions are caused by the biological decomposition of various waste streams and fertilizer; fugitive emissions from chemical processes; fossil fuel production, transmission, and combustion; and many smaller sources. The other gases include HFCs, used primarily as refrigerants; PFCs, released as fugitive emissions from aluminum smelting and used in semiconductor manufacture; and SF₆, used as an insulator in utility-scale electrical equipment. 

Notes