The plot thickens: Debate continues over potential greenhouse gas emissions from natural gas

August 19, 2011 by Ken Ward Jr.

A natural gas well operated by Northeast Natural Energy on Saturday, Aug. 6, 2011.(AP Photo/David Smith)

We’ve written before on this blog about the growing debate over whether relying on natural gas as a “bridge fuel” to quickly reduce greenhouse emissions in the near-term is a sound environmental policy for the nation and world (See here, here and here for previous coverage).

Most recently, a blockbuster study from Cornell University scientists got a huge amount of media attention when it suggested — contrary to conventional wisdom — that gas might be worse than coal when it comes to climate change.

Now, though, there’s another study, this one from researchers at Carnegie Mellon University that suggests that the original conventional wisdom was right all along.  A press release from the university touted the study this way:

Carnegie Mellon University’s Chris Hendrickson, Paulina Jaramillo and their colleagues report that life-cycle greenhouse gas emissions from Marcellus Shale natural gas are not as high as life-cycle greenhouse gas emissions of coal, when used by the electric power sector — the major sector in which these fuels compete.

“Marcellus Shale gas emits 50 percent fewer greenhouse gas emissions than any U.S. coal-fired plant,” said Hendrickson, the Duquesne Light Co. Professor of Engineering and co-director of the Green Design Institute at Carnegie Mellon. “We favor extraction of Marcellus Shale natural gas as long as the extraction is managed to minimize adverse economic, environmental and social impacts.”

Remember that the Cornell study by Robert W. Howarth and others, reported:

The footprint for shale gas is greater than that for conventional gas or oil when viewed on any time horizon, but particularly so over 20 years. Compared to coal, the footprint of shale gas is at least 20 percent greatr and perhaps more than twice as great on the 20-year horizon and is comparable when compared over 100 years.

Now, while Howarth’s study got a lot of press attention, the new Carnegie Mellon paper hasn’t yet been covered much by the mainstream media, aside from this report in the Patriot-News in Harrisburg, Pa.  Look for that to change very soon, as the industry’s public relations machine gears up. The paper is already being promoted here in West Virginia by a pro-drilling bog sponsored by the industry law firm Spilman Thomas and Battle and by John Hanger, the former Pennsylvania environmental commissioner who now consults for industry.

Hanger in particular seems thrilled with the CMU study, writing:

This careful study debunks and decimates professor Howarth’s hit piece study that the NYT gas reporter and other media gave so much attention. By contrast, the CMU study has received very little press attention so the result remains that many people think Howarth is the final word on this important matter.

Now, keep in mind this part of what the CMU study reports:

There is significant uncertainty in our Marcellus shale GHG emission estimates due to eventual production volumes and variability in flaring, construction and transportation.

Not surprisingly, Hager is eager to weigh those uncertainties in a manner that favors gas drilling:

The researchers found that there was virtually no difference between greenhouse emissions from Marcellus shale gas and conventional gas production.

Actually, the CMU researchers report, right in the abstract of their paper:

This represents an 11 percent increase in GHG emissions relative to average domestic gas (excluding combustion) and a 3 percent increase relative to the life cycle emissions when combustion is included.

And later, they write:

Marcellus shale gas adds only 3% more emissions to the average conventional gas, which is likely within the uncertainty bounds of the study.

It’s interesting, though, that Hager says later in the comments section of his blog that:

Gas replacing coal cuts carbon by 20 to 50 per cent and will cut it more with even better regulation which should happen.

Remember that the conventional wisdom has long been that gas produced half of the greenhouse emissions of coal — and that the groundbreaking reporting by Abrahm Lustgarten for ProPublica:

Advocates for natural gas routinely assert that it produces 50 percent less greenhouse gases than coal and is a significant step toward a greener energy future. But those assumptions are based on emissions from the tailpipe or smokestack and don’t account for the methane and other pollution emitted when gas is extracted and piped to power plants and other customers.

The EPA’s new analysis doubles its previous estimates for the amount of methane gas that leaks from loose pipe fittings and is vented from gas wells, drastically changing the picture of the nation’s emissions that the agency painted as recently as April. Calculations for some gas-field emissions jumped by several hundred percent. Methane levels from the hydraulic fracturing of shale gas were 9,000 times higher than previously reported.

When all these emissions are counted, gas may be as little as 25 percent cleaner than coal, or perhaps even less.

Another interesting thing is that, as some readers may recall, the gas industry went after Howarth for speaking his mind about drilling, writing on their Energy in Depth blog:

Although generally well-regarded as a researcher (notwithstanding last year’s “I blew it” moment on the first iteration of his paper), Prof. Howarth is not exactly a dispassionate observer of the current debate over Marcellus development.

Presumably, the industry minds less when researchers are quoted in university press releases saying they “favor” natural gas.

All of that aside, there are differences between the Cornell and the CMU studies that explain at least part of the very contradictory results that were produced. Retired EPA official Wes Wilson explains some of those in this post from the WTFrack.org blog. For example:

Carnegie Mellow authors use the 100 year time period and a factor of 25 for the heat trapping effect of methane greenhouse gas equivalent to CO2 based on the IPCC’s 4th Assessment Report issued in 2007.

Cornell’s Howarth uses a factor of 33 for 100 years and a factor of 105 for 20 years. The global warming potential factors for methane of 33 for 100 years and 105 for the 20 year time period are factors that have been peer reviewed (Lelieveld, et. al. 2005) and a number of experts expect these factors to become the IPCC’s factors in their 2012 report.

The CMU study appears to use an estimated gas leakage rate of 2 percent, while the Cornell study uses more recent EPA data along with other previous studies and comes up with a leakage rate estimate of 3.6 percent to 7.9 percent.

Which study is right? Well, science doesn’t necessarily work that way — much as the back-and-forth, politicized world of blogs and modern media, PR machines from all sides would like. There may be a lot more work needed before there’s a clear answer to guide public policy.

Joe Romm at Climate Progress has provided thoughtful posts on this topic herehere and here.  Among other things, Romm notes a study by the National Energy Technology Laboratory,

… Showing a different result [than Cornell]. NETL looked at both a 100-year timeframe and a 20-year time frame, and in both cases found that life-cycle greenhouse gas emissions from natural gas were substantially lower than coal. According to the findings, natural gas emitted 50% fewer emissions than coal over a 20-year GWP and emitted 55% fewer emissions over a 100-year GWP.

And:

NETL admits that there’s uncertainty in its data collection of production rates, flaring rates and factors related to pipeline transport. But the study does show that natural gas has considerably lower GHG emissions than coal over both a short and long time horizon — when you compare coal burned in a typical (inefficient) coal plant with gas burned in a typical (efficient) baseload plant. So-called simple (or single) cycle gas plants running on unconventional gas may have only marginally lower GHG emissions that coal plants.

Also, NETL uses the IPCC’s 2007 GWP numbers. While that is not unreasonable, Howarth uses the higher GWP of gas from more recent research, which is also reasonable and probably more accurate. NETL also blurs the numbers a little by its use of calculations based on “average generation” and a “domestic mix” of natural gas (conventional and unconventional).

Romm continued:

As Mother Jones’ Kate Sheppard explains

That’s because industry isn’t currently required to report their emissions””and in fact are one of several industries suing the Environmental Protection Agency to keep it that way. Getting the data proved to be “amazingly frustrating,” [Howarth] says. The numbers he and his coauthors used in the study were drawn from a combination of industry reports, presentations, and dated EPA estimates.

Getting these numbers right should be a top priority, which is why I suggest a National Academy of Sciences review.

4 Responses to “The plot thickens: Debate continues over potential greenhouse gas emissions from natural gas”

  1. This is one of the most well-written pieces on the scientific evaluation of shale-gas I’ve read! I myself am writing a short editorial about fracking (for our small Cleveland-based magazine), and appreciate your research on this particular aspect of the issue. Thanks for the unbiased summary of both sides.

  2. M. Sweeney says:

    Another thing to note about the CMU study is that it assumes that the wastewater generated by shale gas extraction will be disposed of in relatively nearby deep injection wells. This is a common disposal method in some parts of the country, but not in Northeast PA, where there are few, if any, deep disposal wells.

    As Wes Wilson notes in the article at WTFrack.org referenced above, the fact that the CMU study made an erroneous assumption about wastewater disposal calls into question the authors’ general knowledge of shale gas extraction operations in the Northeast. The thorny disposal issue in PA has been the subject of news reports in local and national media and my guess would be that anyone who has been following the shale gas news in PA would probably know that deep injection wells are not an option there, so it is quite surprising that a group of researchers at CMU who are writing a paper about shale gas would get this basic fact wrong. This makes me wonder if they may have made other, less obvious errors.

  3. Gary Nickerson says:

    In the overheated environment that surrounds this issue, it is a great pleasure to read this account!

  4. Thank you for a nice, concise, and objective summary of the differences between our paper published last April and the more recent study from our colleagues at Carnegie Mellon. Science is a slow process, best done with reflective time for thought rather than in the immediacy of the blogosphere. Our study will not be the final statement for sure, but I am confident that we were conservative and careful in our analysis, and I believe our conclusions will hold up well over time.

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