BOX 2.1

Preparation of the U.S. Greenhouse Gas Emissions Inventory

Preparation of a national greenhouse gas emissions inventory is a major undertaking, involving many people and agencies in a typical Annex I country. The current version of the IPCC guidelines for inventory preparation is a five-volume set of books with several hundred pages of formulas, supporting data, sample calculations, reporting formats, and technical references. In the United States, the Environmental Protection Agency is ultimately responsible for planning and preparing the national inventory, but it relies on many other agencies and individuals for data, scientific information, analysis, and review. Contributors to the inventory include the Department of Energy, U.S. Department of Agriculture (U.S. Forest Service, Agricultural Research Service, National Agricultural Statistics Service), U.S. Geological Survey, Department of Transportation (including the Bureau of Transportation Statistics), Department of Commerce, Federal Aviation Administration, Department of Defense, and Colorado State University. Many private sector contractors and academic and research institutions from all sectors of the economy also contribute data and analysis to the inventory. The majority of emissions in the U.S. inventory are estimated using the highest-tier methods, and its preparation has stimulated some original research to improve basic understanding and emissions coefficients. The U.S. inventory also undergoes separate expert and public review before publication and submission to the UNFCCC.

combustion comprises the bulk (90 percent) of energy emissions.

The AFOLU sector is responsible for approximately 30 percent of global greenhouse gas emissions (Figure 2.1) but represents a much greater component of emissions in developing countries than in developed countries because of tropical deforestation and lower levels of industrial development. Agriculture contributes 15 percent of emissions in the developing world and deforestation contributes 35 percent. The figures are lower for Annex I countries, with agriculture emissions of less than 10 percent of the total and forests representing a net sink for CO2 (note the negative sign for the Annex I forestry emission in Table 2.1). In contrast, emissions from the industrial and waste sectors in both Annex I and non-Annex I countries are an order of magnitude lower than emissions from the energy and AFOLU sectors.

A second simplifying message is that fewer than one quarter of the 185 countries in the World Resources Institute database were responsible for more than 80 percent of global emissions in 2000 (Figure 2.2). This concentration of sources has increased over the last decade with the surge in fossil-fuel emissions from a few rapidly growing, developing economies. Because developed countries and the largest emitting developing countries are likely to be the focus of mitigation efforts under a new climate treaty, their emissions will be of particular importance for monitoring.

The many activities and gases in the two most important sectors—energy and AFOLU—are cataloged in the next section. The most important gases in these sectors are CO2, CH4, and N2O. Corresponding material for the industrial and waste sectors, including a discussion of CO2, HFCs, N2O, and CH4, is contained in Appendix A.

TABLE 2.1 Sectoral Emissions from Annex I Countries for 2007

  Sector

Fraction of Total Emissionsa

Fraction of Sectoral Emissions by Gas

CO2

CH4

N2O

HFCs

PFCs

SF6

Total

1.00

0.81

0.12

0.06

0.01

0.00

0.00

Energy

0.91

0.94

0.05

0.01

0.00

0.00

0.00

Industrial processes

0.08

0.69

0.00

0.07

0.18

0.03

0.03

Solvent and other product use

0.00

0.48

0.00

0.52

0.00

0.00

0.00

Agriculture

0.08

0.00

0.47

0.53

0.00

0.00

0.00

Land use, land-use change, and forestry (LULUCF)b

–0.09

1.04

–0.03

–0.01

0.00

0.00

0.00

Waste

0.03

0.07

0.90

0.06

0.00

0.00

0.00

Other

0.00

0.95

0.02

0.02

0.01

0.00

0.00

aThe disparate gases were added assuming their global warming potential with a 100-year time horizon. Each number in the table represents the sum of values from the national reports of all Annex I countries. Each value has its own confidence level, which varies with the gas and the national and sectoral source of emissions. No composite uncertainty calculations have been attempted.

bFor Annex I countries, this sector overall is a net sink due to sequestration of CO2. In national inventories, this is shown as negative emissions. Because emissions of CH4 and N2O in this sector are positive, the fraction of LULUCF that they represent is shown as a negative.

SOURCE: <http://unfccc.int/ghg_data/ghg_data_unfccc/items/4146.php>.



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