Remaining sections of this issue brief describe major sources of emissions in each of these categories and outline potential policy options for addressing them.
1. All emissions data in this issue brief are from 2005 and are taken from a report issued by the U.S. Environmental Protection Agency. U.S. EPA, 2007. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 - 2005, EPA 430-R-07-002, EPA: Washington, DC. Available at http://epa.gov/climatechange/emissions/usinventoryreport.html. Accessed August 21, 2007. Fossil fuel combustion accounted for 79 percent of U.S. GHG emissions in 2005; the non-energy use of fossil fuels - as lubricants or feedstocks, for example - accounted for another 2 percent.
2. See Issue Brief #5 on taxes, trading schemes, and standards for further discussion of these regulatory approaches.
3. See Issue Brief #1 on U.S. GHG emissions for a detailed breakdown of these emissions.
4. For example, an EIA analysis from March 2006 that considered a range of cap-and-trade proposals found that with modest near-term GHG permit prices ($8 to $24 (2004 dollars) per metric ton of CO2e in 2020), reductions in other GHGs (i.e., those besides energy-related CO2) would account for 25-55 percent of total emissions reductions in 2020, despite composing only about 6 percent of regulated emissions in the reference scenario. (EIA, 2006. Energy Market Impacts of Alternative Greenhouse Gas Intensity Reduction Goals, SR/ OAIF/2006-01, EIA: Washington, DC.)
5. Offset programs are discussed in Issue Brief #15. Such programs could be used to recognize GHG reductions that involve fugitive emissions, such as methane and nitrous oxide emissions from agricultural activities (over 7 percent of U.S. emissions) and from landfill and wastewater treatment (over 2 percent). (See Issue Brief #13 for further information on specific GHG-reduction opportunities in the agricultural sector.) Some non-traditional GHG emissions may be difficult to regulate under any policy, such as methane emitted during the transmission, storage, and distribution of natural gas (around 1 percent of U.S. GHG emissions) or nitrous oxide from mobile combustion (around 0.5 percent of U.S. GHG emissions).