The federal Energy Information Administration reported Wednesday that U.S. fossil fuel-use-related emissions of carbon dioxide, the most significant global warming greenhouse gas, fell a record 7% last year.

"While emissions have declined in three out of the last four years, 2009 was exceptional," says an EIA statement noting the drop of 405 million metric tons represents the biggest decline in such emissions in six decades, since such tracking began:

"... emissions developments in 2009 reflect a combination of factors, including some particular to the economic downturn, other special circumstances during the year, and other factors that may reflect persistent trends in our economy and our energy use."

Overall, a severe recession in heavy industry and a turn towards a service economy, coupled with drops in transportation, led to the decline, finds the analysis. U.S. gross domestic product plunged 6.3 % last year, the biggest drop since the 1982 recession.

Carbon dioxide is the biggest player in greenhouse gas emissions linked to global warming, concluded the 2007 Intergovernmental Panel on Climate Change. The 2007 Massachusetts vs. EPA Supreme Court decision found the gas a pollutant under the Clean Air Act, leading to ongoing efforts by the Environmental Protection Agency to regulate its use, and discussion of various energy and climate bills in the U.S. Senate.

"As the economy recovers, the structure of that recovery will be important to the future emissions profile of the United States. If energy-intensive industries lead the economic recovery, emissions would increase faster than if service industries or light manufacturing play the leading role," concludes the EIA analysis. "However, longer-term trends continue to suggest decline in both the amount of energy used per unit of economic output and the carbon intensity of our energy supply, which both work to restrain emissions."

By Dan Vergano