Although U.S. total greenhouse gas emissions increased in 1998 for the seventh year in a row, a relatively warm winter and lower emissions in the industrial sector helped constrain that growth to 0.2 percent, compared with average yearly increases of 1.2 percent during the 1990s (see table). The reduction in the rate of increase occurred despite sharply lower crude-oil prices and robust economic growth.

The most important greenhouse gas is water vapor, but human activity contributes negligibly to its atmospheric concentrations. However, concentrations of several other important greenhouse gases-especially carbon dioxide, methane, nitrous oxide, and a group that includes the synthetic gases called halocarbons-are heavily influenced by humans. The United States is a major source of emissions of all these gases.

Carbon dioxide

On a carbon-equivalent basis, carbon dioxide accounts for 83 percent of U.S. emissions of greenhouse gases. All but 2 percentage points of that share is attributable to energy consumption. In 1998, carbon dioxide emissions from the electric utility sector rose 3.2 percent and those from the transportation sector rose 2.4 percent. However, residential and commercial sector emissions remained essentially flat and industrial sector emissions fell 1.3 percent, apparently due to declines in automobile production and in direct fuel use in such industries as steel and chemicals.

Methane

Almost all U.S. methane emissions result from energy production and transport, waste management, and agriculture. Total emissions fell 1.5 percent in 1998, due to more extensive efforts to capture emissions from landfills. Energy-related emissions were unchanged from the previous year, while agricultural emissions (from livestock and their wastes) rose 0.6 percent.

Nitrous oxide

U.S. nitrous oxide emissions dropped 0.5 percent to 103 million metric tons (carbon equivalent) in 1998. Agriculture, mainly nitrogen fertilization of soils, accounts for 71 percent of nitrous oxide emissions. Much of the rest comes from fossil-fuel-burning vehicles with catalytic converters.

Halocarbons and other gases

Emissions of hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride are small compared with those of carbon dioxide, but these engineered gases survive for hundreds or thousands of years in the atmosphere and thus have extremely high global warming potentials. They account for about 2 percent of U.S. emissions on a carbon-equivalent basis. Emissions of these gases grew 3 percent in 1998, somewhat less than in previous years.

Emissions of Greenhouse Gases in the United States 1998, DOE/EIA-0573(98); 170 pages, 58 tables, 12 figures.

Questions about the report's content should be directed to:

Perry Lindstrom, Office of Integrated Analysis and Forecasting

perry.lindstrom@eia.doe.gov

Phone: (202) 586-0934

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File last modified: November 19, 1999