A key selling point for natural gas over coal is that it burns cleaner, releasing less of the greenhouse gases that cause climate change. But a study out this week challenges that assumption when it comes to “unconventional” sources of natural gas such as Pennsylvania’s Marcellus Shale that extends into New York.
Cornell University professor Robert Howarth says if the drilling and extraction of natural gas are taken into account, it’s actually dirtier than coal.
Howarth, who has studied the impact of greenhouse gases for 30 years, said that when he first saw commercials touting natural gas as “greener” and “cleaner,” he started looking for the science to back it up. But he didn’t find any that compared coal and natural gas as far as greenhouse gas emissions.
Howarth just completed his own study that takes into account how much methane leaks during the natural gas drilling process in shale formations, and over the lifetime of a well.
“So if you look over a 100-year time frame, our analysis would say–from a global warming standpoint–coal and natural gas, shale gas, are equally bad.,” Howarth said. “But if you look over a shorter time frame, 20 years or so, than shale gas is far worse than coal.”
Howarth said the methane leakage from shale gas extraction is greater than previously thought. And it’s higher than that produced during the extraction of more conventional natural gas. Howarth said shale gas creates more flow-back water, which contains methane.
But the study, which Howarth said is the first of its kind, will likely stir up debate between natural gas advocates and opponents.
Chris Tucker of the industry-sponsored Energy In Depth said the report is full of holes. Tucker challenges the 20-year time frame used by Howarth. The United Nations and the federal Environmental Protection Agency both use a 100-year time frame to measure the impact of coal and natural gas emissions on global warming. If a 100-year time frame were used, the impact of natural gas would lessen; that’s because methane dissipates much more quickly than carbon dioxide.
Tucker questioned the quality of the data. Howarth himself said the data was hard to come by, and poorly documented. But, he said, the bulk of the information came from the industry itself.
Tucker also questioned Howarth’s objectivity on the subject, saying he is an outspoken opponent of natural gas drilling in New York state.