updated 12/3/2008 6:56:30 PM ET 2008-12-03T23:56:30

The amount of U.S. greenhouse gases flowing into the atmosphere, mainly carbon dioxide from burning fossil fuels, increased last year by 1.4 percent after a decline in 2006, the Energy Department reported Wednesday.

The report said carbon dioxide, the leading pollution linked to global warming, rose by 1.3 percent in 2007 as people used more coal, oil and natural gas because of a colder winter and more electricity during a warmer summer. Half of the country's electricity is generated by coal-burning power plants.

A shortage of hydropower also contributed to an increase in the demand for fossil fuels, said the department's Energy Information Administration.

The EIA said that in 2007 the United States produced 8 billion tons of greenhouse gases, compared to 7.9 billion in 2006. The tonnage, presented in terms of "carbon dioxide equivalent" also includes methane, nitrous oxides and a number of lesser greenhouse gases, although carbon dioxide accounted for nearly 83 percent of the releases.

Increases seen worldwide
Despite a growing concern about the accumulation of heat-trapping pollution that scientists say is changing the world's climate, the flow of greenhouse gases continue to increase not only in the United States, but worldwide.

U.S. greenhouse gases have increased 16.7 percent since 1990, or an average of 0.9 percent a year, the EIA report. Carbon dioxide emissions have increased an average of 1.1 percent a year since 1990.

Globally the increases have been even more dramatic, according to separate findings by scientists at the Oak Ridge National Laboratory. They showed carbon dioxide output worldwide increased by 3 percent from 2006 to 2007 with a 7.5 percent increase in China, according to data released earlier this year.

"We have not been able to turn our emissions around. We still are increasing our emissions overall," said Brenda Ekwurzel, a climate scientists at the Union of Concerned Scientists.

Last year, President Bush touted the 2006 reduction in U.S. greenhouse gas emissions as evidence that his largely voluntary efforts to address climate change was making headway as carbon dioxide releases dropped 1.3 percent between 2005 and 2006. And Bush also noted the continued drop in "carbon intensity" — carbon dioxide emission increases as related to economic growth — which has declined steadily since 1990.

Warmer winter reflected in '06 decline
But the EIA noted the reductions in 2006 simply reflected the year's warmer than normal winter which cut demand for fuel oil and natural gas, and a moderate summer that reduced demand for coal-generated electricity for air conditioners.

Likewise, said the EIA, the 2007 increase in emissions "resulted primarily from two factors: unfavorable weather conditions, which increase demand for heating and cooling in buildings, and a drop in hydropower availability that led to greater reliance on fossil energy sources (coal and natural gas) for electricity generation."

U.S. carbon intensity barely declined in 2007, falling by a meager 0.6 percent, compared to an annual average decline of 1.9 percent since 1990 and 2.1 percent since 2002, said the report.

In addition to the 6.6 billion tons of carbon dioxide, there were emissions in 2007 of 772 million tons of methane and 422 tons of nitrous oxides, both increasing about 2 percent, and 195 million tons of other greenhouse gases, an increase of 3 percent. All numbers are carbon equivalent.

Copyright 2008 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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