Greenhouse gas (GHG) emissions in the United States, which had grown at an average annual rate of 0.7% since 1990, were 7,053 million metric tons carbon dioxide (CO2) equivalent in 2008, a 2.2% decrease compared with 7,210 million metric tons in 2007, according to a report released Thursday by the Energy Information Administration (EIA). Natural gas, which accounted for 28.5% of fossil energy used in the United States in 2008, accounted for only 21% of total energy-related CO2 emissions.
The overall decrease in GHG emissions was largely the result of a 3% drop in CO2 emissions resulting primarily from higher energy prices that led to a drop in petroleum consumption, economic contraction that resulted in lower energy demand, and lower demand for electricity, according to the report. Lower carbon intensity in the electricity fuel mix also helped to lower emissions in 2008, EIA said.
While CO2 accounted for 82.8% of the total estimated U.S. GHG emissions in 2008, methane (10.5%) and nitrous oxide (4.3%) were also emitted in significant amounts, EIA said. Hydrofluorocarbons, perfluorocarbons and sulfur hexafluoride made up less than 2.5% of total emissions.
Energy-related CO2 emissions dominate total GHG emissions in the United States. Petroleum is the largest fossil fuel source for energy-related emissions, accounting for 42% of all energy-related emissions in 2008, EIA said. Coal is the second largest contributor at 37%.
The electric power sector is the largest energy-related source of emissions, accounting for 40.6% of energy-related CO2 emissions, according to the report. The transportation sector is the second largest source (33.1%), while direct fuel use in the residential and commercial sectors, along with the use of fuels to produce heat in the industrial sector contributed another 26.3%.
Energy-related CO2 emissions, which had risen at an average annual rate of 1% from 1990 to 2007, decreased 2.9% in 2008, driven down primarily by record-high oil prices and the economic downturn, EIA said.
While U.S. emissions declined in 2008, global concentrations of CO2, methane and nitrous oxide reached the highest levels recorded since pre-industrial times, according to the World Meteorological Organization, an agency of the United Nations (see NGI, Nov. 30a).
The GHG observations come on the eve of climate talks in Copenhagen, Denmark (see related story). The White House has said that President Obama is prepared to put on the table a U.S. emissions reduction target of 17% below 2005 levels in 2020 and ultimately inline with final U.S. energy and climate legislation when he travels to Copenhagen on Wednesday (see related story; NGI, Nov. 30b).
Charges and counter-charges have been flying based on the recent release of hundreds of documents and e-mail exchanges between leading climate scientists from Britain's Climate Research Unit (CRU) at the University of East Anglia that were obtained by hackers. Opponents of the theory that human activities, particularly GHG emissions, are to blame for climate change claim the purloined documents reveal efforts by some research scientists to manipulate data to support a massive worldwide campaign to retard climate change. On Tuesday CRU director Phil Jones announced that he would "step aside" until the completion of an independent review of the incident. Sen. James Inhofe of Oklahoma, the ranking Republican on the Senate Environment and Public Works committee, has called for a congressional hearing.
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