Does shale gas pollute more than coal?
An abundant source of U.S. natural gas widely seen as a cleaner alternative to oil and coal is in reality the fossil fuel that creates the most greenhouse gas emissions, a study concludes.
The paper led by Cornell University ecology professor Robert Howarth raised howls of protest from the gas industry, which said the document was political.
The study contends that so much methane escapes from the extraction of shale gas over the life of a well that it allows more heat-trapping greenhouse gas into the atmosphere than coal.
The report acknowledged that natural gas is cleaner to burn than other fuels but that greater pollution derives from leakage, whether accidental or purposely designed to relieve well pressure.
Improved technology could solve the problem but Howarth in an interview doubted whether that was economical considering stubbornly low natural gas prices. A North American boom in the production of shale gas, billed as an alternative to foreign oil, has depressed gas prices even while oil has soared.
Industry representatives criticized the work as sloppy and incomplete advocacy against shale gas. The shale boom previously had raised more alarm from environmentalists because of the threat of chemicals seeping into ground water through the drilling process known as hydraulic fracturing, or "fracking."
Some 3.6 percent to 7.9 percent of the methane from shale gas production leaks into the atmosphere, releasing a greenhouse gas that is especially potent over the first 20 years, the study said.
"Compared to coal, the footprint of shale gas is at least 20 percent greater and perhaps more than twice as great on the 20-year horizon and is comparable when compared over 100 years."