Emissions of Greenhouse Gases in the United States 1998

This edition of Emissions of Greenhouse Gases in the United States provides annual estimates of U.S. nitrous oxide emissions from the nitrogen fertilization of agricultural soils that are approximately 50 percent larger than those in previous editions. For 1998, the additional 0.232 million metric tons of nitrous oxide are equivalent to 20 million metric tons of carbon or 1.1 percent of all U.S. greenhouse gas emissions. For 1990, the additional 0.198 million metric tons of nitrous oxide are equivalent to 17 million metric tons of carbon or 1.0 percent of all U.S. Greenhouse gases (see Table ES2). For a discussion on the estimation method used, see Appendix A.

Previously, estimated emissions from nitrogen fertilization of agricultural soils included direct emissions from the use of commercial synthetic fertilizers, the application of animal manure, crop residues, and emissions from soil mineralization. In addition, previous emissions estimates included indirect emissions from leaching and atmospheric deposition. The addition of nitrous oxide emissions from the biological fixation of nitrogen in agricultural soils to this year's estimates increases total emissions of nitrous oxide from the nitrogen fertilization of soils by 48 percent in 1990 and 57 percent in 1998 (see Table 25).

Estimates of emissions from fertilizer use are highly uncertain. Models used for estimation are based on limited sources of experimental data. The uncertainty increases when moving from emissions associated with animal manure to soil mineralization and atmospheric deposition, where both estimating emissions and partitioning emissions between anthropogenic and biogenic sources become increasingly difficult.

In addition, this year's report has been revised to include nitrous oxide emissions from the consumption of wood in the residential, industrial, and electric utility sectors, pursuant to the 1996 Revised IPCC Guidelines for National Greenhouse Gas Inventories.