Life cycle greenhouse gas (GHG) emissions from natural gas-fueled power plants are the same whether they are fueled with gas from shale or conventional basins, according to a study published in the Proceedings of the National Academy of Sciences.

The study, "Harmonization of Initial Estimates of Shale Gas Life Cycle GHG Emissions for Electric Power Generation," also confirmed that the life cycle emissions for any gas-fired power generation source are only half as much as those from coal-fired electricity.

Multiple authors from strategic energy analysis centers in the National Renewable Energy Laboratory (NREL) in Golden, CO, applied what they described as a "meta-analytical technique called harmonization" to compare existing studies estimating the life cycle GHG emissions from shale gas, conventional natural gas and coal.

Since previous published studies and articles about GHG emissions have come to widely differing conclusions, NREL Senior Scientist Garvin Heath said the use of harmonization "helps to clarify the existing knowledge on this important topic," providing a more "apples-to-apples" comparison.

Heath and the study's other co-authors, Patrick O'Donoughue, at NREL, and Douglas Arent and Morgan Bazilian from the Joint Institute for Strategic Energy Analysis, headed a team of researchers that screened hundreds of published life cycle assessments (LCA) for quality and relevance today, including dozens of studies related to conventionally produced natural gas and shale gas.

Going forward, the authors emphasized the importance of actual GHG emission measurements to advance the understanding of energy options for climate change strategists. While they see their analytical work adding more consistency to the current body of knowledge, they also note that alternative assumptions in the future, such as comparing median gas-fired plants LCA emissions to the cleanest possible coal-fired electricity, might turn up less of a spread between the two under those assumptions.

If the gas-fired units' emissions began to approach the emissions from the "best-performing coal units," that could carry implications for future climate change mitigation strategies, the authors said.

The new harmonization of the prior GHG emissions compared data provides more precision, but it has its limitations, according to Arent.

"It does not fully address the questions of accuracy of our knowledge of GHG emission sources in the natural gas supply chain," said Arent, adding that the researchers raised those questions in a recent separate article in Science magazine.

"As called for in that article and this one, verified measurements of emissions from components and activities through the natural gas supply chain and robust analysis of lifetime well production and prevalence of practices to reduce emissions, can help create a more robust understanding of our energy options."