Natural gas extracted from shale formations has a greater greenhouse gas footprint in the form of methane emissions than conventional gas, oil and coal over a 20-year period, according to research published online in the journal Climatic Change Letters.
Researchers say this calls into question the logic of its use as a climate-friendly alternative to fossil fuels. The research was conducted by Robert Howarth and colleagues from Cornell University in New York.
Howarth and team evaluated the greenhouse gas footprint of natural gas, obtained by high-volume hydraulic fracturing of shale formations, focusing on methane emissions. They analyzed recently published data, in particular, the technical background document on greenhouse gas emissions from the oil and gas industry as well as a report on natural gas losses on federal lands from the General Accountability Office.They calculated that overall during the life cycle of an average shale-gas well, between 4 to 8 percent of the total production of the well is emitted to the atmosphere as methane, via routine venting and equipment leaks, as well as with flow-back return fluids during drill out following the fracturing of the shale formations.
They said routine production and downstream methane emissions are comparable to those of conventional gas. Methane is a more potent greenhouse gas than carbon dioxide, but also has a 10-fold shorter residence time in the atmosphere. As a result, its effect on global warming falls more rapidly. Researchers said methane dominates the greenhouse gas footprint for shale gas on a 20-year horizon, contributing up to three times more than direct carbon dioxide emission. At this time scale, the footprint for shale gas is at least 20 percent greater than that for coal, perhaps twice as great.
Howarth said, "The large greenhouse gas footprint of shale gas undercuts the logic of its use as a bridging fuel over coming decades, if the goal is to reduce global warming."
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