Executive Summary

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Figure ES-15: U.S. Greenhouse Gas Emissions Per Capita and Per Dollar of Gross Domestic
Product (GDP)
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Source: BEA (2016), U.S. Census Bureau (2016), and emission estimates in this report.
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Key Categories
The 2006 IPCC Guidelines (IPCC 2006) defines a key category as a “[category] that is prioritized within the
national inventory system because its estimate has a significant influence on a country’s total inventory of
greenhouse gases in terms of the absolute level, the trend, or the uncertainty in emissions and removals.” 27 By
definition, key categories are sources or sinks that have the greatest contribution to the absolute overall level of
national emissions in any of the years covered by the time series. In addition, when an entire time series of emission
estimates is prepared, a thorough investigation of key categories must also account for the influence of trends of
individual source and sink categories. Finally, a qualitative evaluation of key categories should be performed, in
order to capture any key categories that were not identified in either of the quantitative analyses.
Figure ES-16 presents 2015 emission estimates for the key categories as defined by a level analysis (i.e., the
contribution of each source or sink category to the total inventory level). The UNFCCC reporting guidelines request
that key category analyses be reported at an appropriate level of disaggregation, which may lead to source and sink
category names which differ from those used elsewhere in the Inventory report. For more information regarding key
categories, see Section 1.5 – Key Categories and Annex 1.
27 See Chapter 4 “Methodological Choice and Identification of Key Categories” in IPCC (2006). See
26 DRAFT Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2015