PA develops the national greenhouse gas inventory each year to track the national trend in emissions and removals since 1990. The national greenhouse gas inventory is submitted to the United Nations in accordance with the Framework Convention on Climate Change (http://unfccc.int/national_reports/items/1408.php (not a EPA site)). In preparing the annual emissions inventory report, EPA collaborates ... with hundreds of experts representing more than a dozen U.S. government agencies, academic institutions, industry associations, consultants and environmental organizations.
The U.S. greenhouse gas inventory also presents emissions by more commonly used economic categories: agriculture, commercial, electricity generation, industry, residential and transportation. Using this categorization, emissions from electricity generation accounted for the largest portion of U.S. greenhouse gas emissions in 2006. Transportation activities accounted for the second largest portion and emissions from industry comprised the third largest portion. The agriculture, commercial and residential economic sectors, listed in descending order of their contribution, together account for the remaining U.S. greenhouse gas emissions.