Methane emissions increase
Methane emissions increase
Methane is a potent greenhouse gas for global warming. Although methane accounts for only 14 percent of emissions worldwide, it traps up to 86 times more heat than carbon dioxide over a 20-year period.

The concentration of methane in the atmosphere stabilized from about 1999 to 2007, but since 2007 has begun rising again (see graphic ). In 2007 U.S. emissions of methane from human-related sources were 33.4 teragrams of carbon equivalent per year (Tg/yr), about 10% of global methane emissions.

GOSAT satellite observations

The GOSAT satellite (the world's first satellite dedicated to greenhouse-gas-monitoring launched by Japan in 2009) measures the densities of carbon dioxide and methane in the Earth's atmosphere at 56,000 locations. GOSAT observations have a low spatial resolution, but the satellite revisits the same ground location every 3 days, which makes the observations well suited for temporal trend analyses. Statistical analysis of the GOSAT data indicates that in the contiguous U.S. methane concentration is increasing by 2.5%/year over the 2010–2014 period. In the central part of the U.S. the trends are higher. For example, the trend in Oklahoma is a 4.7%/year increase in methane concentration.

These results show that U.S. methane emissions have increased by more than 30% over the 2002–2014 period. The increase is largest in the central part of the U.S.
Methane emission increase
Methane emissions increase
As can be seen from the graph, the study was not able to identify the source of the methane because of the geographic overlap of livestock and oil and gas production in the U.S. and the limited resolution of the spatial pattern of the methane increase seen by satellite.

The renewed growth in global atmospheric methane between 2005 and 2010 is estimated to be due to an increase in global methane emissions of 17–22 teragrams per year (Tg/yr). Of this, the new GOSAT results suggest that increasing U.S. anthropogenic methane emissions account for up to 30–60%. The authors state that more research is required into U.S. anthropogenic methane emissions, particularly those from the livestock and oil and gas sectors.

These new results contrast with EPA estimates which indicate that emissions remained flat over this period. This study and others have provided significant new data on methane emitted by existing operations in the oil and gas sector that show that "methane emissions are substantially higher than we previously understood" according to the EPA Administrator. The EPA's next annual methane report was due to be published in April 2016. The U.S. EPA inventory only provides national totals, so identifying sectors responsible for the increase is difficult. The U.S. EPA is currently developing a spatially resolved version of their methane emissions inventory.

Implications of this research

To this point the shale oil and gas sector in the U.S. has been exempted from protections under the federal Clean Air Act, Clean Water Act, and other environmental laws. In 2012, the Environmental Defense Fund (EDF) initiated a series of independent projects designed to find out how much and from where methane is escaping into the atmosphere across the entire natural gas supply chain: production; gathering lines and processing facilities; long-distance pipelines, storage, and local distribution; as well as some end users using natural gas, commercial trucks and refueling stations. This investigation involved nearly 100 research and industry experts. The results of these studies suggested that current EPA data both underestimate the magnitude of methane emissions and mask the rise in U.S. methane emissions over the past decade. Some of the results found by the EDF studies include the following:

  • Scientists collected data using aircraft and ground-based platforms in the Texas Barnett Shale. Using this data they estimated regional and facility-level methane emissions and found that regional methane emissions are 50 percent higher than estimates based on the EPA’s Greenhouse Gas Inventory.

  • Methane emissions from local gas distribution systems were also investigated it was and found that methane emissions from local natural gas distribution systems are significant. The EDF and Google Earth Outreach released interactive maps that show methane leaking from pipelines under city streets.

  • The Denver-Julesburg Flyover Study found that methane emissions were three times higher than estimates derived from EPA data.

  • A study assessed the spatial distribution of anthropogenic methane sources in the United States by combining comprehensive atmospheric methane observations, extensive spatial datasets, and a high-resolution atmospheric transport model. Based on the results of this analysis the study concluded that the EPA underestimates methane emissions nationally by a factor of 1.5 X, and regionally by 4.9 X.

Because of the research reported here and that from the EDF and others, the U.S. Environmental Protection Agency (EPA) has begun to regulate methane emissions. In May 2016 the EPA issued standards to regulate methane emissions from new and modified sources of oil and gas. It has also begun a formal process leading to rule setting for existing oil and gas sources. The objective is to reduce methane emissions from the U.S. oil and gas sector by 40 to 45 percent below 2012 levels by 2025

Turner, A. J., D. J. Jacob, J. Benmergui, S. C. Wofsy, J. D. Maasakkers, A. Butz, O. Hasekamp, and S. C. Biraud (2016), A large increase in U.S. methane emissions over the past decade inferred from satellite data and surface observations, Geophys. Res. Lett., 43, 2218–2224, doi:10.1002/2016GL067987.

Environmental Defense Fund Studies on Methane Emissions

Anthropogenic emissions of methane in the United States, Scot M. Miller, Proceedings of the National Academy of Sciences, vol. 110 no. 50 (2013), doi: 10.1073/pnas.1314392110

EDGAR Methane

U.S. EPA Oil and Natural Gas Air Pollution Standards