The United States emitted nearly 1 percent more greenhouse gases in 2005 than it did in 2004, according to an emissions inventory from the Environmental Protection Agency. From 1990 to 2005, the country's greenhouse-gas emissions rose 16.3 percent.

The leading greenhouse gases released in the United States are carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride. In 2005, the combined output of these gases was equivalent to the emission of 7,260 billion kilograms of carbon dioxide.

Carbon dioxide discharged by fossil fuel combustion accounted for 79 percent of the 2005 total. Forty-one percent of this carbon dioxide was from electricity generation, and 33 percent came from ground and air transportation, the agency reported on April 15.

Landfills, coal mining, and natural gas systems are the major human-caused sources of methane, while nitrous oxide arises mainly from fertilizer applications and other farming practices, along with the burning of fuel for transportation.

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