The release of 11 research papers Tuesday marked another milestone in the Environmental Defense Fund's ongoing effort to understand the natural gas industry's carbon footprint. Overall, the studies found that emissions of methane––a greenhouse gas at least 34 times more potent than carbon dioxide––in the Texas Barnett Shale were 50 percent higher than estimated by the Environmental Protection Agency.

The EDF-sponsored research adds to a growing body of work on the amount of methane leaking from natural gas operations, and the results are crucial for understanding whether natural gas will accelerate or delay the effects of climate change as it's increasingly used in place of coal.

Dozens of scientists from 20 universities and private research firms contributed to the 11 studies, collectively called the "Barnett Coordinated Campaign." Twelve research teams took measurements over an area that included 30,000 oil and gas wells, 275 compressor stations and 40 processing plants. All of the studies were published in the peer-reviewed journal Environmental Science & Technology. Another study that synthesizes the papers' results will be published later.

The Barnett campaign is a major part of EDF's $18 million methane study series. Launched in 2011, EDF's project has won praise for the scope of its research and the scientists' unprecedented access to well sites, which allowed them to take direct measurements at emission sources. But EDF has also been criticized for working closely with industry and for requiring researchers to sign nondisclosure agreements that prevent them from sharing preliminary results with the scientific community.

The scientists behind the Barnett campaign used both "top-down" methods—where emissions are measured from aircraft over a large area—and "bottom-up" methods, where emission sources such as pneumatic valves and compression stations are individually measured and tallied up. Both methods showed that a large portion of the leaks come from a relatively small number of "super-emitters." The scientists also used chemical "fingerprints" to distinguish the methane emitted by oil and gas production from the methane coming out of landfills and agricultural sources. One of these "fingerprints" is ethane, a light gas that's found only in fossil fuel-produced methane.

Nine of the 11 studies were published for the first time on Tuesday (the other two were published online several months ago but still considered part of the Barnett campaign). One of the nine papers summarizes the campaign's main findings. A guide to the remaining eight studies is below:

1. Methane Emissions from Leak and Loss Audits of Natural Gas Compressor Stations and Storage Facilities

Authors : Derek R. Johnson, April N. Covington, and Nigel N. Clark

Summary : Scientists measured the methane emitted from three compressor stations and two natural gas storage facilities to better understand the specific pieces of equipment responsible for the emissions. Only 12 percent of the emissions came from unintentional leaks caused by malfunctions; the rest of the methane came from engine exhaust, pneumatic equipment, valves, vents, and tanks.

2. Aircraft-Based Estimate of Total Methane Emissions from the Barnett Shale Region

Authors : Anna Karion, Colm Sweeney, Eric A. Kort, Paul B. Shepson, Alan Brewer, Maria Cambaliza, Stephen A. Conley, Ken Davis, Aijun Deng, Mike Hardesty, Scott C. Herndon, Thomas Lauvaux, Tegan Lavoie, David Lyon, Tim Newberger, Gabrielle Pétron, Chris Rella, Mackenzie Smith, Sonja Wolter, Tara I. Yacovitch, and Pieter Tans

Summary : Aircraft-based measurements from March and October 2013 found methane emissions that were consistent with the EPA's national estimates. But the measured emissions were higher than emissions reported by industry to EPA under the Greenhouse Gas Reporting Program. They were also higher than the numbers found in EDGAR, a greenhouse gas inventory headed by the European Commission's Joint Research Center and the Netherlands Environmental Assessment Agency.

3. Characterizing Fugitive Methane Emissions in the Barnett Shale Area Using a Mobile Laboratory

Authors : Xin Lan, Robert Talbot, Patrick Laine, and Azucena Torres

Summary : Researchers measured methane emissions downwind of landfills and oil-and-gas facilities (well pads, compressor stations and gas processing plants) by driving a mobile laboratory around north Texas. Some of the highest emission rates came from landfills and compressor stations; some of the lowest rates came from well pads.

4. Aircraft-Based Measurements of Point Source Methane Emissions in the Barnett Shale Basin

Authors : Tegan N. Lavoie, Paul B. Shepson, Maria O. L. Cambaliza, Brian H. Stirm, Anna Karion, Colm Sweeney, Tara I. Yacovitch, Scott C. Herndon, Xin Lan, and David Lyon

Summary : Researchers outfitted an aircraft to measure methane emission rates from eight major sources (three landfills and five oil-and-gas facilities) in Texas' Barnett Shale region. The measurements were higher than emissions determined by previous efforts, including the U.S. EPA Greenhouse Gas Reporting Program.

5. Constructing a Spatially Resolved Methane Emission Inventory for the Barnett Shale Region

Authors : David R. Lyon, Daniel Zavala-Araiza, Ramón A. Alvarez, Robert Harriss, Virginia Palacios, Xin Lan, Robert Talbot, Tegan Lavoie, Paul Shepson, Tara I. Yacovitch, Scott C. Herndon, Anthony J. Marchese, Daniel Zimmerle, Allen L. Robinson, and Steven P. Hamburg

Summary : An inventory of methane emissions from various sources across Texas' Barnett Shale region in October 2013 determined that the oil-and-gas sector was responsible for more than half of the area's emissions. The researchers' calculation of oil-and-gas emissions was higher than existing estimates from alternative inventories, such as the EPA's Greenhouse Gas Inventory.

6. Airborne Ethane Observations in the Barnett Shale: Quantification of Ethane Flux and Attribution of Methane Emissions

Authors : Mackenzie L. Smith, Eric A. Kort, Anna Karion, Colm Sweeney, Scott C. Herndon, and Tara I. Yacovitch

Summary : Top-down measurements taken from aircraft showed that 71 to 85 percent of the methane emissions in the Barnett Shale region came from fossil fuel activities. The scientists used ethane as a tracer to identify fossil fuel-based methane.

7. Integrating Source Apportionment Tracers into a Bottom-up Inventory of Methane Emissions in the Barnett Shale Hydraulic Fracturing Region

Authors : Amy Townsend-Small, Josette E. Marrero, David R. Lyon, Isobel J. Simpson, Simone Meinardi, and Donald R. Blake

Summary : The researchers used ethane and chemical isotopes––distinct varieties of an element such as carbon or hydrogen––to trace the "fingerprints" of methane emitted by landfills, agriculture and oil-and-gas sites in the Barnett region. They found that hydrogen isotopes (rarely used in these types of studies) are a useful tool that can distinguish between methane emitted by natural gas wells versus oil wells.

8. Toward a Functional Definition of Methane Super-Emitters: Application to Natural Gas Production Sites

Authors : Daniel Zavala-Araiza, David Lyon, Ramón A. Alvarez, Virginia Palacios, Robert Harriss, Xin Lan, Robert Talbot, and Steven P. Hamburg