Both the U.S. Environmental Protection Agency (EPA) and the Energy Information Administration (EIA) estimate annual U.S. GHG emissions. EPA is responsible for producing the official inventory of U.S. emissions, as required under the United Nations Framework Convention on Climate Change. Both agencies use EIA fuel consumption data as a basis for estimating most GHG emissions, but differences in their methodologies can result in different datasets.1 EIA usually releases its data about six months before EPA. EPA provides more detail of interest to transportation, such as emissions by mode. EIA presents emissions in million metric tons of carbon equivalent (mmtce), while EPA uses teragrams of carbon dioxide equivalent (TgCO2Eq), as required under the Convention.2
1 For more information, see U.S. Department of Transportation, Bureau of Transportation Statistics, Transportation Statistics Annual Report 2001 (Washington, DC: 2002), p. 239, also available at http://www.bts.gov.
2 TgCO2Eq = 1 mmtce x (44/12).