Greenhouse gas (GHG) emissions inventories and reporting has emerged as a leading issue at the state, regional and federal levels in the United States (US) and Canada. Methane (CH4) and carbon dioxide (CO2) emissions are the chief greenhouse gases related to natural gas transmission and storage. Several new initiatives have been launched or are currently under development in the US and Canada that establish rules to report and track these emissions.
According to the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2005 total U.S. GHG emissions in 2005 were 7260.4 million metric tonnes (MMT). Of that amount, 6089.5 MMT (80 percent) was CO2 emissions from fuel combustion. Combustion of natural gas accounted for 1170 MMT, 20% of the CO2 from combustion and 16 % of the total GHG emissions.
The natural gas industry had direct GHG emissions of 232 million metric tonnes of CO2 equivalent (MMTCO2e) in 2005, 3.2 percent of the total GHG emissions for the U.S. The transmission and storage segment of the natural gas industry had emissions of 68.8 MMT CO2e, less than 1 percent of the U.S. total. This included 31.9 MMT CO2 from the combustion of “pipeline fuel” and 36.8 MMT CO2e from the release of methane. Thus, direct emissions from pipelines were 68.8 MMT CO2, while the CO2 content of gas throughput was 1170 MMT CO2e.
The gas transmission industry CO2 emissions comprise just 0.5 percent of U.S.GHG emissions.
Natural gas is composed primarily of methane and methane is a GHG itself, with a global warming potential 21 times higher than CO2. That means that one ton of methane has the global warming effect of 21 tons of CO2. Leaks and venting of natural gas (methane) comprise the second component of GHG emissions related to natural gas. Fugitive methane emissions from the natural gas industry account for approximately 20% of total U.S. methane emissions and about 2% of total U.S. GHG emissions.
Natural gas production operations had total emissions of 83.0 MMTCO2e, which included 6.4 MMTCO2e from non-energy related emissions, mostly natural gas flaring, 41.4 MMTCO2e from the combustion of “lease fuel” (gas consumed for operations at the producing site), and 35.2 MMTCO2e from the fugitive release of methane.
Natural gas processing operations had total emissions of 53.0 MMTCO2e, including 19.4 MMTCO2e from the combustion of “plant fuel” (gas combusted in the processing operations), 21.7 MMTCO2e of non-energy CO2 emissions primarily from acid-gas removal units, and 11.9 MMTCO2e equivalent from the fugitive release of methane.
The transmission and storage segment of the natural gas industry had emissions of 68.8 MMTCO2e, which is 29.6 percent of the gas industry’s total and 0.9 percent of the U.S. total. This included 31.9 MMTCO2e from the combustion of pipeline fuel and 36.8 MMTCO2e from the fugitive release of methane. Distribution operations had emissions of 27.4 MMTCO2e from the fugitive release of methane.
Overall, about half of the GHG emissions from the natural gas industry are from the release of methane. The natural gas industry emitted 20.6% (111.1 MMTCO2e) of all U.S methane emissions, 6.8 percent of which is from the transmission and storage segment of the natural gas industry.
U.S. EPA, Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2005 (2007). This is the source for all data in this section unless otherwise noted.