U.S. Greenhouse Gas Emissions Still Increasing
Total U.S. greenhouse gas (GHG) emissions were 7,282 million metric tons carbon dioxide equivalent (MMTCO 2e) in 2007, an increase of 1.4 percent from the 2006 level according to Emissions of Greenhouse Gases in the United States 2007, according to a report released December 4 by the Energy Information Administration (EIA). Since 1990, U.S. GHG emissions have grown at an average annual rate of 0.9 percent.U.S. GHG emissions per unit of gross domestic product (GDP), or U.S. GHG intensity, fell from 636 metric tons per million 2000 constant dollars of GDP (MMTCO 2e/million dollars GDP) in 2006 to 632 MMTCO 2e /million dollars GDP in 2007, a decline of 0.6 percent. Since 1990, the annual average decline in GHG intensity has been 1.9 percent.Total estimated U.S. GHG emissions in 2007 consisted of 6,022 million metric tons of carbon dioxide (82.6 percent of total emissions); 700 MMTCO 2e of methane (9.6 percent of total emissions); 384 MMTCO 2e of nitrous oxide (5.3 percent of total emissions); and 177 MMTCO 2e of hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF 6) (2.4 percent of total emissions).Emissions of carbon dioxide from energy consumption and industrial processes, which had risen at an average annual rate of 1.1 percent per year from 1990 to 2006, increased by 1.3 percent in 2007. Unfavorable weather patterns, where both heating and cooling degree-days were higher in 2007 than 2006, and an increase in the carbon intensity of electricity generation, driven by decreased availability of hydropower, both contributed to higher energy-related carbon dioxide emissions in 2007. Methane emissions increased by 1.9 percent, while nitrous oxide emissions rose by 2.2 percent. Emissions of HFCs, PFCs, and SF6, a group labeled collectively as “high-GWP gases” because of their high heat-trapping capabilities, increased by 3.3 percent.