Total U.S. greenhouse gas emissions have dropped 1.5 percent. GHG emissions were 7,075.6 million metric tons carbon dioxide equivalent in 2006, a decrease of 1.5 percent from the 2005 level according to Emissions of Greenhouse Gases in the United States 2006, a report (PDF) released by the Energy Information Administration.
Since 1990, U.S. GHG emissions have grown at an average annual rate of 0.9 percent. The 2006 emissions decrease is only the third decline in annual emissions since 1990.
U.S. GHG emissions per unit of Gross Domestic Product, or “U.S. GHG-intensity,” fell from 653 metric tons per million 2000 constant dollars of GDP (MTCO2e/$Million GDP) in 2005 to 625 MTCO2e /$Million GDP in 2006, a decline of 4.2 percent. Since 1990, the annual average decline in GHG-intensity has been 2.0 percent.
Total estimated U.S. GHG emissions in 2006 consisted of 5,934.4 million metric tons of carbon dioxide, 605.1 MMTCO2e of methane, 378.6 MMTCO2e of nitrous oxide, and 157.6 MMTCO2e of hydrofluorocarbons, perfluorocarbons and sulfur hexafluoride.
Emissions of carbon dioxide from energy consumption and industrial processes, which had risen at an average annual rate of 1.2 percent per year from 1990 to 2005, declined by 1.8 percent in 2006. The decline in carbon dioxide emissions from 2005 to 2006 can be attributed to a one-half percent decline in overall energy demand and a decrease in the carbon intensity of electricity generation.
Favorable weather patterns, where both heating and cooling degree-days were lower in 2006 than 2005, and higher energy prices, were the primary causes of lower total energy consumption. The decline in carbon intensity of electricity generation was driven by increased use of natural gas, the least carbon-intensive fossil fuel, and greater reliance on non-fossil fuel energy sources.
Methane emissions, meanwhile, decreased by 0.4 percent, while nitrous oxide emissions rose by 2.9 percent. Emissions of HFCs, PFCs, and SF6, a group labeled collectively as “high-GWP gases” because their high heat trapping capabilities, fell by 2.2 percent.