Methane 

Figure Data

U.S. anthropogenic methane emissions totaled 611.9 MMTCO₂e⁵ (26.6 million metric tons of methane) in 2005, representing 8.6 percent of total U.S. greenhouse gas emissions. Methane emissions in 2005 were 0.9 percent (5.3 MMTCO₂e) higher than the 2004 level of 606.5 MMTCO₂e (Table ES4). The increase is attributable primarily to increases in methane emissions from landfills (6.9 MMTCO₂e) and, to a lesser extent, emissions associated with animal husbandry. Those increases were offset to some degree by a decrease in methane emissions from coal mines (1.8 MMTCO₂e) and a small decrease in emissions from the cultivation of crops. Despite the 0.9-percent increase in 2005, methane emissions still were 89.8 MMTCO₂e (13 percent) below their 1990 level of 701.7 MMTCO₂e. 

Methane emissions come from four source categories, three major and one minor. The major sources are energy, agriculture, and waste management, and the minor source is industrial processes. The three major sources accounted for 42, 30, and 28 percent, respectively, of total 2005 U.S. emissions of methane. Trends in the major sources of anthropogenic methane emissions since 1990 are illustrated in Figure ES4. 

Energy Sources 

Total U.S. energy consumption fell by 0.3 percent from 2004 to 2005; and methane emissions from energy sources (coal mining, natural gas systems, petroleum systems, stationary combustion, and mobile source combustion) in 2005, at 254.9 MMTCO₂e, were 1.3 percent below the 2004 level of 258.3 MMTCO₂e. Methane emissions from energy sources have fallen by 7.3 percent since 1990. 

Agricultural Sources 

Methane emissions from agricultural sources, at 183.0 MMTCO₂e, represented 30 percent of total U.S. anthropogenic methane emissions in 2005. Emissions increased by 1.0 percent (1.9 MMTCO₂e) in 2005 relative to 2004. Increases greater than 1 percent in emissions from enteric fermentation in domesticated animals and from animal waste were offset to some extent by decreases in emissions from rice cultivation and burning of crop residues. Of the total 2005 methane emissions from agricultural sources, 93 percent (170.9 MMTCO₂e) resulted from livestock management, of which 68 percent (115.6 MMTCO₂e) was from enteric fermentation and the remainder (55.3 MMTCO₂e) was from anaerobic decomposition of livestock wastes. Methane emissions from rice cultivation (10.9 MMTCO₂e) and crop residue burning (1.2 MMTCO₂e) together represented about 6.6 percent of total methane emissions from agricultural sources in 2005, which have increased by 5.5 percent since 1990. 

Waste Management 

Methane emissions from waste management, which at 171.5 MMTCO₂e accounted for 28 percent of U.S. anthropogenic methane emissions in 2005, were 4.3 percent above the 2004 level of 164.5 MMTCO₂e. Landfills—the largest single source of U.S. anthropogenic methane emissions—represented 91 percent (155.7 MMTCO₂e) of total U.S. methane emissions from waste management in 2005. The remainder of 2005 methane emissions from waste management (15.8 MMTCO₂e) was associated with domestic wastewater treatment. Methane emissions from waste management have fallen by 32 percent (79.1 MMTCO₂e) from their 1990 level of 250.6 MMTCO₂e, due largely to increased methane recovery at landfills, which increased to 122.5 MMTCO₂e in 2005 from 21.7 MMTCO₂e in 1990. Even at these higher methane recovery levels, however, waste management emissions, after bottoming out in 2002, increased in both 2004 and 2005. 

Industrial Processes 

Methane emissions from industrial processes totaled 2.5 MMTCO₂e in 2005, including 1.5 MMTCO₂e from chemical manufacturing and 1.0 MMTCO₂e from iron and steel production. The 2005 total was 7.7 percent below the 2004 total of 2.7 MMTCO₂e. Since 1990, growth in methane emissions from chemical production has been more than offset by reductions in emissions from iron and steel production, leaving the 2005 total for industrial process emissions 8.4 percent below the total for 1990.

Notes