Total US greenhouse gas (GHG) emissions were 7,075.6 million metric tons carbon dioxide equivalent (MMTCO2e) in 2006, a decrease of 1.5% from the 2005 level, according to Emissions of Greenhouse Gases in the United States 2006, a report by the Energy Information Administration (EIA).
Total greenhouse gas emissions from the transportation sector rose 0.5% from 2005 to 2006, reaching 2,010.3 MMTCO2e. Carbon dioxide emissions represented 93.75% of total transportation GHG in 2006 (1,884.7 MMTCO2).
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| Transportation sector emissions from gasoline and diesel fuel combustion generally parallel total vehicle miles traveled. Click to enlarge. |
Transportation sector carbon dioxide emissions in 2006 were 407.5 million metric tons higher than in 1990, an increase that represents 46.4% of the growth in unadjusted energy-related carbon dioxide emissions from all sectors over the period.
Since 1999, the transportation sector has led all US end-use sectors in emissions of carbon dioxide. Petroleum combustion is the largest source of carbon dioxide emissions in the transportation sector, as opposed to electricity-related emissions in the other end-use sectors.
Increases in ethanol fuel consumption in recent years have mitigated the growth in transportation sector emissions somewhat (emissions from energy inputs to ethanol production plants are counted in the industrial sector).
US GHG emissions per unit of Gross Domestic Product (GDP), or 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%. Since 1990, the annual average decline in GHG-intensity has been 2.0%.
Total estimated US GHG emissions in 2006 consisted of 5,934.4 million metric tons of carbon dioxide (83.8% of total emissions), 605.1 MMTCO2e of methane (8.6% of total emissions), 378.6 MMTCO2e of nitrous oxide (5.4% of total emissions), and 157.6 MMTCO2e of hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulfur hexafluoride (SF6) (2.2% of total emissions).
Emissions of carbon dioxide from energy consumption and industrial processes, which had risen at an average annual rate of 1.2% per year from 1990 to 2005, declined by 1.8% in 2006. The decline in carbon dioxide emissions from 2005 to 2006 can be attributed to a 0.5% 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%, while nitrous oxide emissions rose by 2.9%. Emissions of HFCs, PFCs, and SF6, a group labeled collectively as “high-GWP gases” because their high heat trapping capabilities, fell by 2.2%.
The 2006 emissions decrease is only the third decline in annual emissions since 1990. Since 1990, US GHG emissions have grown at an average annual rate of 0.9%. GHG emissions in 2006 were 15.1% higher than those in 1990.
– from http://www.greencarcongress.com/