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.