Greenhouse Gases and Global Warming

Greenhouse gas emissions in the United States increased slightly between 1990 and 1993, according to the Inventory of U.S. Greenhouse Gas Emissions and Sinks compiled by the U.S. Environmental Protection Agency (September 1994). In 1990, the first year such data was collected and the base level against which future greenhouse gas emissions will be measured, total greenhouse gas emissions were 1,444 million metric tons carbon equivalent (MMTCE). Following a reduction in 1991 to 1,432 MMTCE in 1991, the level jumped up to 1,452 MMTCE in 1992.

Carbon dioxide emissions from fossil fuel combustion account for about 92% of total greenhouse gas emissions, with other sources including CO2 from cement manufacture; methane from landfills, agriculture, and coal mining; and nitrous oxide (N2O) from agriculture and fossil fuels. CFCs and HCFCs are not included in the inventory because they are being phased out, though HFCs (hydrofluorocarbons) and PFCs (perfluorinated compounds) are included and accounted for 20 MMTCE in 1993. Forests in the U.S. provided a net sink of 117 MMTCE in 1992. The U.S. has committed to reducing greenhouse gas emissions to 1990 levels by the year 2000.