Wednesday, August 17, 2011

Carnegie Mellon Life Cycle Gas Study Debunks Howarth Claims

Drawing virtually no press attention, 6 researchers at Carnegie Mellon University published on August 5th a detailed study of life cycle greenhouse gas emissions of Marcellus Shale gas.

The study concluded that Marcellus shale gas is much cleaner than coal when greenhouse gas pollution is used to compare the environmental impact of gas and coal. The study specifically analyzed the carbon footprint of Marcellus gas and not other shale reservoirs. The study was also reviewed prior to publication by the Sierra Club.

It is a careful piece of work that lays out the data used, the assumptions made, and conclusions reached.

The Carnegie Mellon researchers find: "Natural gas from the Marcellus shale has generally lower life cycle GHG emissions than coal for production of electricity in the absence of any effective carbon capture and storage processes, by 20-50% depending upon plant efficiencies and natural gas emissions variability."

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

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.

The lead researcher of the CMU paper is Mohan Jiang of the Civil and Environmental Engineering Department. W Michael Griffin, Chris Hendrickson, Paulina Jaramillo, Jeanne VanBriesen, and Aranya Venkatesh also authored the study. The Tepper School of Business and the Department of Engineering and Public Policy also participated in the study.

The paper was published in Environmental Research Letters. Go to    The study is a must read if you are interested in science and truth and should get much more publicity and recognition.


  1. Concerned ScientistAugust 17, 2011 at 9:43 AM

    Thanks for this John. I had not heard about it until now when I heard about the Howarth et al paper before it was published. That tells you something.

    One key finding - Marcellus Shale gas is roughly the same as the average conventional gas in terms of GHG emissions. I'd even argue that eventually they will be less due to stronger regulations in PA, NY etc. It is also that much closer to market and will be using newer pipelines.

    It seems like there are a few key variables that control the GHG emissions of natural gas and shale gas in particular

    1) the efficiency of the power plant - this seems to be the key variable so we should all push for the most efficient plants

    2) the amount of gas produced in the well - the greater the volume, the less GHGs per unit of energy. So more effective frac jobs and optimal well drilling are better for the environment. Table 4 is very telling - it shows that if a well produces 10 million cubic feet per day (MMCFD), the preproduction emissions (this is fracking, drilling, testing, etc) total less than 1% of the total life cycle emissions. Most Marcellus wells are producing in the 2-20 MMCFD range, so the drilling and fracking emissions are a rounding error when compared to the emissions from combustion.

    3) venting and flaring at the well site - the authors suggest that improvements can be made with green completions but that this is not going to change the bottom line that much for wells that produce at a high rate. For more marginal wells this will play a progressively greater role in reducing total life-cycle emissions. It is still a good and worthy goal however and will help conserve energy at the same time.

    So much of the comparison comes down to the efficiency of the power plant. It be very helpful to compare some old inefficient coal plants with modern highly efficient gas plants they would likely be replaced with. I imagine this number could be >>50% less GHG emissions for highly efficient gas pants vs old inefficient coal plants.

    A good and welcome paper.

    BTW it's HowaRth, not HoRwath. I made that same mistake for quite some time.

  2. Nice scoop, John.

    Remarkable, to me, the delayed, low-key rollout on the CMU paper, compared to the media tsunami which carried the Cornell paper.

    Are the anti-drillers more polished in the PR Department?

  3. Thank you. In answer to your question, "yes." Howarth had the big advantage of saying something outrageous or shocking or bad news...all of which has more market. He also had an advantage of the NYT gas reporter and his huge barrel of ink that is important in of itself but also sets the anti-gas narrative that some in the media pack follow. If you know the NYT gas reporter is going to put something in the NYT, then some reporters feel almost a need to put the same stuff in their paper. It is a competitive business and nobody wants to feel left behind or out. The Duke study authors had the university PR machine promote that study. The authors had a next day op-ed ready to go for papers around the country. Unlike Howarth, the Duke study has value, though the authors wanted to emphasize the gas migration finding and not mention much at all their finding that no frack fluids/chemicals had returned from depth to contaminate anyone's water wells...a finding that the PA DEP also had made.

  4. This is cherry picking at its worst.

    The Sierra Club reviewed this paper, as stated in the Acknowledgments "We gratefully acknowledged the financial support from the Sierra Club……and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the Sierra Club" The Cornell study and the CMU study aren’t all that different in their conclusions. Gas still doesn’t look great, and the difference comes when estimating the amount of fugitive methane, methods used during production (such as venting) and the ultimate end use of the gas. CMU is more conservative with their numbers, Cornell not as much.

    What’s troubling about this is how industry and some journalists are using the study to combat the Howarth study, cherry picking small pieces of the study, and not others.

    This Study generally shows that gas, while cleaner than coal during combustion (which we all knew already), it still contributes significantly to GHG emissions. These fugitive emissions seriously erode any advantage natural gas has over coal, and shows significant reason why methane must be regulated.

  5. I agree methane emissions and leakage should be regulated. Doing so will increase gas' large carbon advantage over coal EPA has proposed important rules to regulate methane leakage. The CMU study finds that Marcellus gas has same carbon footprint as conventional gas and emits 20 to 50% less than coal on a lifecycle basis. NETL study supports CMU. CMU conclusions are very different than horvath who told the world shale gas was as dirty or dirtier than coal. He repeated that false claim in many interviews. If he was misquoted I never saw a letter from him setting the record straight.

  6. Concerned ScientistAugust 18, 2011 at 12:46 PM


    Where do you see cherry picking? I did not see any cherry picking going on in what John Hanger wrote.

    What is better - current levels of GHG emissions or half of current levels of GHG emissions? If we could cut our emissions in any other area by 50% the Sierra Club and others would be doing anything they could to make sure that happened.

    Switching from coal to gas is like switching from an SUV to a Prius. It really is.

    Would you say that switching from an SUV to a Prius is barely worth doing because a Prius is still a car that produces emissions? You'll lose a lot of the Sierra Club members with that argument.

    One of the key points of the paper is that wells that produce a lot of gas like Marcellus wells, the percentage of the GHG emissions that comes from what they called preproduction (drilling, fracking, venting, etc) becomes trivial (<1% of the total) when examined on a life cycle basis. It would be better if that could be reduced, but on a life cycle basis, almost everything but combustion becomes a rounding error with wells that produce a lot of gas. Say 50 million cubic feet of gas is flared or lost during drilling (this is a random number chosen to prove a point). If the well only produces 1 billion cubic feet, that 50 million makes up 5% of the total. If that well produces 5 BCF it only makes up 1% of the total. So the emissions associated with drilling and transportation become trivial when compared with those that come from combustion. It is in combustion and end use that gas really is way better than coal. So gas from highly productive Marcellus wells is way better than coal from a GHG perspective (and way way better in terms of mercury, sulfur dioxide, soot, and other pollutants).

    If the Marcellus wells were poor producers, this argument would have a lot more to it and there may be some areas where the Marcellus doesn't produce as much. In these areas, this will become much more of a concern because fugitive emissions will represent a much higher percentage of the total emissions per unit of energy produced if something isn't done to reduce them. Therefore, companies should be encouraged or compelled to adopt practices that minimize precombustion emissions of all kinds so that when the wells aren't quite as good, gas is still significantly better than coal.

  7. Concerned Scientist,

    I will admit that cherry-picking was a bit harsh, but then again Mr. Hanger's headline was also a bit over the top as well!

    As for the studies, they used different factors and different weightings to determine the effect of methane on climate change. Different data input different results out. a brief summary of the differences are as follows:

    Carnegie Mellon authors used 100 year time period and a factor of 25 for the heat trapping of methane GHG equivalent to CO2 based on the IPCC's Assessment Report Cornell's Howarth uses a factor of 33 for 100 years
    Carnegie Mellon cites methane industry leakage at 2% based on EPA 1996. In 2011 EPA updated its estimates of methane emissions which significantly increased the rates of methane release from a number of sources. Howarth used factors between 3.6%-7.9%

    In a blog post critiquing the Carnegie Mellon study, retired EPA analyst Wes Wilson said the following regarding this blog post " The cover story offered in the blog by John Hanger , the former director of the Pennsylvania DEP, states: "The researchers found that there was virtually no difference between greenhouse emissions from Marcellus shale gas and conventional gas production." This conflicts with what EPA has reported in its 2011 update of emission factors as noted above. In fact the very abstract from Carnegie Mellon does comport with Mr. Hanger's claim as it states that shale gas has an 11% net higher emissions that conventional gas.

    As a colleague of mine stated, and I agree with this statment "Any way you look at (shale gas) fracking, imho, it's bad. It's too expensive, diverts resources, capital from renewable resources of energy, too dangerous, and overall adds to global climate change. It is not a "bridge fuel, clean or safe."

  8. David:

    1. From section 8 of the CMU study, "For comparison purposes, Marcellus shale gas adds only 3% more emissions to the average conventional well, which is likely within the uncertainty bounds of the study."CMU finds no statistical difference between a Marcellus well and a conventional gas well. That is a fact.

    2. CMU did NOT use just the 1996 study to arrive at it's 2% leakage rate. It clearly states it used EPA 2010 data too. As I understand it the 2% leakage rate is an independent CMU calculation for Marcellus specifically. The EPA data was national and used as a means to check the CMU number. The 2% rate is higher than the 1996 EPA data I believe but could be wrong.

    3. If shale gas is really too expensive, you will not have to worry about it. But it is now providing 30% of all gas and has caused natural gas prices to crash to $4 from $13 in 2008. Gas is replacing coal because of this low price. No shale gas. No low price. And no replacement of coal.

    4. I agree that renewables should be accelerated and nobody has done more than me to make that a reality in PA. Nationally counting corn ethanol, large hydro, all renewables, renewables account for 11% of all us energy. Say that triples by 2020 (unfortunately it will not do that) and renewables provide 33% of all energy by then, where do you want to get the other 67%? coal, oil, nuclear, or gas? Gas is by far the best answer for the remainder. Or do u really believe coal is better? Or oil? Or nuclear?

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

    6. The CMU study conservatively estimates gas' carbon advantage because it uses a very conservative estimate of well production.

  9. It's the Urbina blindnesss, corrupting new folks daily.

    If your emotional and motivational premise is that shale gas is bad, then you'll naturally sort and interpret all information so as to support that premise.

    That's what happened with the NYT people, and with the Cornell people. They are all pretty motivated. People in NY have been pretty well freaked out.

  10. Has anybody taken a look at the report "Lifecycle greenhouse gas emissions from shale gas compared to coal: an analysis of two conflicting studies" produced by J. David Hughes of the Post Carbon Institute? It was released last month and is posted at

    Hughes's paper sought to resolve a study by Timothy Skone of NETL (who found NG to have a lower GHG footprint than coal) with the findings of the Howarth study.

    Hughes's conclusions were that the choice of the 20-year vs 100-year time horizon for methane, as well as the assumption for lifetime well productivity, both have a big influence on whether shale or coal have the lower GHG footprint.

    The same difference seems to largely apply to the difference between the CMU and Cornell studies.

    I am saddened by some of the reaction to these two articles. Maybe I'm naive, but looking at the timeline of when the articles were submitted and published, they came across to me as being two independent assessments of a complex phenomenon, in which some assumptions are debatable. Note that the CMU study did not mention Howarth's paper at all (at least I didn't see it).

    Also, please note the last sentence in the CMU abstract. Those authors, like Howarth et al., point to uncertainties in the data included in their analysis.

    One takeaway from reading the CMU study is that the question of which energy source has the lower GHG footprint is FAR from being settled science. We need more research teams conducting field-based measurements of fugitive methane emissions throughout the Marcellus play to help us really understand what's really going on. Without those field-based studies - that SOMEBODY will need to fund - this discussion will continue as an exercise in arm-waving.

    To cheer one study, and ridicule another, as one might act during a CMU-Tartans vs Cornell-Big Red basketball game, is not how we want to translate science into sound public policy.

  11. It's great to see that a reputable scientific study has finally been completed on this issue, as opposed to the much ballyhooed (and admittedly flawed and incomplete) study by Cornell. And thankfully this cannot be easily dismissed as pro-gas propaganda since it was funded by the Sierra Club.

    However, I think that much is being lost during this discussion of carbon emissions. While carbon and global warming is the hot topic of the day (no pun intended) there are host of other pollutants that have a much more significant impact on human health.

    Mercury, arsenic, barium, nitrous oxide, sulfur dioxide, particulate matter, etc.

    While Mr. Hanger has very well documented these other pollutants and just how much cleaner natural gas is, it's very rare that I see them mentioned in the media, or anywhere outside of this blog really.

    To me, this is the real scandal. How can people who count themselves as environmentalists continue to ignore the drastic, game-changing, monumentally massive improvements to air quality that a natural gas based economy will afford us and our children? This blog has cited studies that say 17,000+ lives will be saved annually by switching to natural gas. Hundreds of thousands of cases of asthma (many among children) will be prevented. In Pennsylvania, 1 in 6 women have mercury levels in high enough concentrations to result in birth defects. What do the "anti's" choose to focus on? One pollutant, and the fact that is ONLY reduced by 50%. Un-freaking-believable! And the sad irony is that many of the loudest voices in opposition to even safe, well regulated natural gas production are here in Pennsylvania, a state with horrible air quality that stands to benefit the most (both economically and environmentally) from such production.

    I'm not even going to start on how much more viable natural gas production makes wind and solar power. That's a whole other can of worms.

    It is the inherent best interest of anyone who happens to breathe air to be championing natural gas production.

  12. Ken:

    Check out the National Energy Technology Laboratory paper on life cycle gas and coal carbon comparisons.

    I blogged on it here. See the archive.