Study: Marcellus Gas Cleaner than Coal [Times Leader, Wilkes-Barre, PA]
Carnegie-Mellon University last week released a study that found natural gas from the Marcellus Shale has 20 to 50 percent lower life cycle greenhouse gas emissions than coal for producing electricity, even without any effective means to capture and store emissions at well sites.
“It essentially refutes the Howarth and Ingraffea study that focused on greenhouse gas emissions from natural gas production,” said John Krohn, spokesman for the Energy In Depth Northeast Marcellus Initiative.
Cornell researchers Robert Howarth, Renee Santoro and Anthony Ingraffea, estimated in the previous study that between 30 and 200 percent more methane is emitted from Marcellus Shale gas produced from the hydraulic fracturing, or fracking, of wells than from conventional gas, coal and oil.
Krohn said the Carnegie Mellon study “used more scientifically accepted approaches to the study of natural gas emissions and their impact on the environment over time.”
John Hanger, former secretary of the state Department of Environmental Protection, agrees.
100-year standard used
Hanger said the Howarth study looked at the effects of methane produced from Marcellus Shale gas on the atmosphere over a 20-year period rather than a 100-year period.
He said the International Panel of Climate Change recognizes the 100-year standard when studying the Global Warming Potential of greenhouse gases because carbon dioxide, a major greenhouse gas, remains in the atmosphere for more than 100 years.
Hanger believes Howarth and his colleagues “cherry-picked” the 20-year perspective because methane – a major component of Marcellus Shale gas – completely dissipates in the atmosphere after only 15 years.
Hanger also said Howarth reached a “very high leakage rate” for the amount of greenhouse gas that escapes from each well site, assuming that all gas escaping wells is vented into the atmosphere and only looking at four or five wells in the entire country.
He said industry practice is to capture and market as much flowback methane as possible and flare much of the rest.
Hanger also pointed out that IHS Cera, an energy information company from which Howarth’s study pulled data, recently published a report stating that IHS data in the Howarth report was “misused and severely distorted.”
“Howarth and his colleagues want to ban hydraulic fracturing and are opposed to shale development,” Hanger said, charging that the Cornell researchers “wanted a very high number” for methane emissions because “(Howarth) wanted to make the claim that gas is as dirty as or dirtier than coal.”
Different take on studies
Ken Klemow, associate director of the Wilkes University-based Institute for Energy and Environmental Research of Northeastern Pennsylvania, had a different take on the two studies.
“I think a lot of people are saying that the Carnegie-Mellon study is sort of a slap in the face to the Cornell researchers and refutes their study. But at no point do (Carnegie-Mellon researchers) mention the Cornell study. The authors did not set out to refute the Cornell study. They looked at things in a somewhat different way and came to different conclusions,” Klemow said.
Klemow said that from a 20-year perspective, methane has 75 times more greenhouse potential than carbon dioxide, but from a 100-year perspective, it has only 25 times more greenhouse potential than carbon dioxide. He said the Cornell researchers “took the worst-case scenario.”
Klemow said he was impressed by the fact that the Carnegie-Mellon researchers “did a good job of trying to track down all the possible sources of Marcellus Shale emissions,” such as tree removal and construction of well pads.
But he also had several questions about the Carnegie-Mellon study that he said were not answered in the report.
Expert poses questions
First of all, Klemow noted, researchers prefer data sets with relatively low standard deviations. Carnegie-Mellon’s standard deviations “were pretty high, meaning there is quite a lot of uncertainty in the numbers going into the study,” which he said the authors acknowledged in the study.
Klemow also noted that some data that should have been the same in both studies “didn’t match up,” such as the grams of carbon released per amount of energy produced.
“They’re off by a factor of two. I would be interested in knowing why the numbers are off.”
Klemow said many researchers rely on data provided by the U.S. Environmental Protection Agency and previous studies, but the Carnegie-Mellon study didn’t note whether it relied on previous data or “went out in the field and used their own measurements.”
The bottom line, Klemow said, is whether natural gas has a lower greenhouse gas footprint than coal.
“The Carnegie-Mellon study tips the balance more in favor of natural gas. But the main thing is that it’s by a little bit. People are saying the CMU study slam-dunks the Cornell study. I’m not really sure about that. I am sure there’s still a lot of work that needs to be done. We really need to get out and take some more field measurements rather than rely on data from previous studies,” Klemow said.Contact Person: Steve Mocarsky, Staff Writer
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