
The economic downturn is primarily responsible, in addition to improvements in both both demand-side efficiency and lower carbon intensity on the supply side.
Total estimated U.S. GHG emissions in 2009 consisted of 5,446.8 million metric tons of carbon dioxide (82.8% of total emissions); 730.9 MMTCO2e of methane (11.1% of total emissions); 219.6 MMTCO2e of nitrous oxide (3.3% of total emissions); and 178.2 MMTCO2e of hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6) (2.7% of total emissions).
Emissions of energy-related carbon dioxide decreased by 7.1% in 2009, having risen at an average annual rate of 0.8% per year from 1990 to 2008. Methane emissions increased by 0.9%, while nitrous oxide emissions fell by 1.7% in 2009.






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