To frack or not to frack?

In a recent op-ed in the New York Times, Geosciences Professor Susan Brantley and public policy expert Anna Meyendorff argued that “the facts on fracking” are mostly in favor of the practice, and that “… if natural gas displaces coal, then fracking is good not only for the economy but also for the global environment.” While we agree with several statements made in that article, a critical environmental impact, namely leaks, was treated inadequately by the authors. So it shall be considered here.

Existing, but yet limited research on atmospheric composition near shale-gas wells shows that fugitive methane emissions from the recent, rapid development of this unconventional natural gas source is possibly higher than presumed by EPA and the industry. If so, a large fraction of US CO2 emissions reductions attributed to shale-gas displacing coal as energy source may be undone by increased emissions of the much stronger greenhouse gas methane. This post shall summarize the specific knowledge development in the last two years.

The shale gas development controversy

Use of “fracking”, shorthand for hydraulic fracturing, has led to a large increase in natural gas production in the US, and is likely going to be practiced in other countries, such as the UK, in the near future. Fracking of rock, namely shale, at different depths releases initially large amounts of (“shale“-) gas, natural gas composed mostly of methane, which cannot be mined from the shale by conventional means. Fracking and its implications have been in the news for several years now, particularly due to (peer-reviewed) findings of methane-contaminated water-wells in areas where fracking is prevalent [1], but also due to findings of increased ambient air pollutant concentrations, such as benzene. There is a very critical documentary, there are blogs, and there even is a Hollywood movie now. All along, the industry has been aggressively defending its fracking endeavors, including with a documentary-style video and TV commercials. Suffice it to say, fracking is highly controversial in the US.

I was approached in summer 2011 at a gathering in San Antonio, TX, on what I thought about fracking. I replied with what I thought true: That there is no doubt that burning natural gas instead of coal drastically reduces combustion-related CO2 emissions per unit electric or heat-energy produced and that the current fracking boom, despite what I then considered to be localized issues with water and air contamination, was on the whole beneficial with respect to reducing greenhouse gas emissions. At that time, I had not yet read one of the very few peer-reviewed studies on the topic by Howarth et al. (2011)[2], which showed that fugitive methane emissions from the investigated shale-gas development may be significantly higher than from conventional natural gas development. Table 2 from that publication is reproduced below.

 Table 2 from Howarth 2011 paper

Total methane emissions may even be as high as to negate the natural gas’ greenhouse savings (compared to burining coal) if leak rates are applicable to the industry as a whole. The paper was followed by an interesting discussion in Nature [3, 4]. It did not take long before critical comments of the study appeared, including a peer-reviewed comment [5] and its rebuttal [6]. Another study, this time by NOAA researchers [7], appeared in 2012, again calculating higher than presumed methane (and associated other hydrocarbon) leak rates. That was contrasted by another publication arguing that actual emissions are much lower than estimated from bottom-up calculations [8].

Why is the leak rate so important?

Basically all studies comparing the life cycle greenhouse gas emissions of various fossil fuels find significant benefits of using natural gas as compared to coal, e.g. [9-12]; and find minor differences between conventional gas and shale gas [13]. However, these studies generally calculate from available inventory data over the lifetime of the well that the leak rate is around one percent of production. Critical for such estimates is which potentially leaking processes are included, and what emissions are assumed for each.

As the dominant component of natural gas is methane, leaks should be avoided as much as possible and the remainder abated (e.g. via flaring). This is because methane, molecule by molecule, is a powerful greenhouse gas, 25-72 times as effective compared to CO2. However, general practice in the industry includes for instance (natural gas) venting (to the atmosphere).

Through climate modeling, and assuming a range of different leak rates as gas replaces coal, Wigley [14](and references therein) showed that only at low leak rates, such as assumed by the industry [3], a transition from coal to gas confers the benefits attributed to it:

The most important result, however, […], is that, unless leakage rates for new methane can be kept below 2%, substituting gas for coal is not an effective means for reducing the magnitude of future climate change.

Another study by Alvarez et al. in PNAS [15] suggests that a leak rate around 3% would still be tolerable, especially when viewed over longer time scales. Whether low leak rates have been and are accomplished in shale gas exploration is coming more into question via some new research carried out in 2012 [16]. While the previous NOAA pilot study (which covered a larger region of oil and gas development in Colorado) from 2008 has been disputed [17, 18], newer data presented during the AGU 2012 Fall Meeting does not appear to paint a better picture. Throughout three sessions entitled Atmospheric Impacts of Oil and Gas Development, several research groups showed highly elevated methane concentrations in areas of new gas development. An example from the abstract of Caulton et al. (presentation A21J-03. Quantifying Methane Emissions from Shale Gas Wells in Pennsylvania) is shown below:

 ambient methane in fracking area

Figure 1: CH4 distribution over southwestern Pennsylvania on 6/21/12 between 9:00 and 10:30 EDT plotted in Google Earth.

Similar results were obtained in Dish, Texas, by Khan et al. (Presentation A21J-04. Fugitive greenhouse gas emissions from shale gas activities – a case study of Dish, TX), and by Presto et al. (Poster A23B-0204. Atmospheric Impacts of Marcellus Shale Gas Activities in Southwestern Pennsylvania), while lower enhancements were reported by Ramos-Garcés et al. (Poster A23B-0203. Methane and its Stable Isotope Signature Across Pennsylvania: Assessing the Potential Impacts of Natural Gas Development and Agriculture). All abstracts can be accessed via the Fall Meeting’s webpage.

High ambient abundances of methane do not necessarily equate to high leak rates. However, with the help of meteorological data, elevated methane concentrations in plumes from the fracking sites can be converted into real-world emissions data. Several authors noted that higher methane abundances occurred in areas with more active development. Simply assuming that shale gas development has similar leak rates than conventional natural gas development over the lifetime of the well is not accurate. This is because shale gas well production declines rapidly [4] within the first two to three years. Thus, the industry has to keep up with well decline through constantly drilling new wells. But as fugitive methane emissions occur dominantly during well development, the shorter lifetime of a shale gas well means larger methane emissions per marketed natural gas. A recent study by the Joint Institute for Strategic Energy Analysis [19] highlights the variability of calculated lifetime fugitive methane emissions based on well production variability in the Texas Barnett shale area. The average emissions were estimated to be 1.3%, but ranged from 0.8 to 2.8% for the Barnett shale area depending on well productivity. The report acknowledged accounting differences, such as compared to the Howarth et al. [2] estimates. It further highlighted that many of these fugitive emissions are preventable and that

… better and more recent measurements of fugitive emissions from well and processing equipment, as well as pipelines at all stages—gathering, transmission, and distribution lines—are warranted because the existing data are sparse and old.

Unfortunately, as the gas price is currently so low, there is also little incentive yet to invest in equipment to minimize fugitive emissions.

Many results presented at AGU are likely to enter the peer-reviewed literature in 2012. They may not conclusively answer the critical question of what a regionally representative leak rate of the current rapid shale gas development is. But a larger study asking this question is already underway. Meanwhile, the development of standards for shale gas exploration, such as this one, suggest that similar problems can be prevented in Europe and elsewhere.

An old problem

The shale gas controversy reminds us the other greenhouse gas problem our fossil fuel dominated energy system contributes to: (fugitive) methane and other hydrocarbon emissions. A recent review [20] suggests that 24% of all man-made methane emissions are due to fossil fuel infrastructure (18% from oil and gas plus 6% from coal mining). The authors’ Figure 1, reproduced below, shows that man-made emissions may still be growing.

 global anthropogenic methane emissions

Figure 2. (a) Methane concentration in the atmosphere. (b) Anthropogenic methane emissions by source in 2010. (c) Anthropogenic methane emission by sectors in 2010. (d) Methane emission trends by sectors from 1990–2010.

On the other hand, a recent study by Simpson et al. [21] showed that the past decline in methane atmospheric growth rate between the mid-1980s and 2010 was likely in large part due to “reduced fugitive fossil fuel emissions”. Another study presented during the AGU Fall Meeting, Schwietzke et al. (Poster A23B-0206. Reducing Uncertainty in Life Cycle CH4 Emissions from Natural Gas using Atmospheric Inversions), is aiming at constraining the average global leak rate from natural gas use. The preliminary results suggest that leak rates as high as 6% are unlikely. Unfortunately, both of these views are global and cannot directly inform about fugitive emissions from shale gas development.

Locally, old and ageing infrastructure is the other recognized source of fugitive emissions. As recently shown by Phillips et al. [22], storing, transporting and using natural gas has its own leak issues. As they showed (Figure 3), there are numerous gas leaks throughout Boston.

elevated methane mixing ratios in Boston

Figure 3.  A total of 3,356 methane leaks (yellow spikes) above background levels of 2.5 ppm mapped across Boston’s 785 road miles (red). source

What conclusions can we draw?

The brouhaha about shale gas development is hardly an invention of some leftwing greenies. There are some clear scientific objections and uncertainties, not only on the water side, but also with respect to atmospheric emissions. Critical questions asked now may prevent future regrets. Even moderate voices are calling for a tighter regulation of the industry, peer-reviewed science provides evidence that such regulation is justified, and a major international risk management company suggests tight planning, careful extraction, and environmental impact monitoring.

So instead of business as usual, critical questions ought to be asked, including whether touting shale gas as a "bridge fuel" is actually justified [23].


1.    Osborn, S.G., A. Vengosh, N.R. Warner, and R.B. Jackson, Methane contamination of drinking water accompanying gas-well drilling and hydraulic fracturing. Proceedings of the National Academy of Sciences of the United States of America, 2011. 108(20): p. 8172-8176.

2.    Howarth, R.W., R. Santoro, and A. Ingraffea, Methane and the greenhouse-gas footprint of natural gas from shale formations. Climatic Change, 2011. 106(4): p. 679-690.

3.    Tollefson, J., Air sampling reveals high emissions from gas field. Nature, 2012. 482(7384): p. 139-140.

4.    Howarth, R.W., A. Ingraffea, and T. Engelder, Natural gas: Should fracking stop? Nature, 2011. 477(7364): p. 271-275.

5.    Cathles, L.M., L. Brown, M. Taam, and A. Hunter, A commentary on "The greenhouse-gas footprint of natural gas in shale formations" by RW Howarth, R. Santoro, and Anthony Ingraffea. Climatic Change, 2012. 113(2): p. 525-535.

6.    Howarth, R.W., R. Santoro, and A. Ingraffea, Venting and leaking of methane from shale gas development: response to Cathles et al. Climatic Change, 2012. 113(2): p. 537-549.

7.   Petron, G., G. Frost, B.R. Miller, A.I. Hirsch, S.A. Montzka, A. Karion, M. Trainer, C. Sweeney, A.E. Andrews, L. Miller, J. Kofler, A. Bar-Ilan, E.J. Dlugokencky, L. Patrick, C.T. Moore, T.B. Ryerson, C. Siso, W. Kolodzey, P.M. Lang, T. Conway, P. Novelli, K. Masarie, B. Hall, D. Guenther, D. Kitzis, J. Miller, D. Welsh, D. Wolfe, W. Neff, and P. Tans, Hydrocarbon emissions characterization in the Colorado Front Range: A pilot study. Journal of Geophysical Research-Atmospheres, 2012. 117.

8.   O'Sullivan, F. and S. Paltsev, Shale gas production: potential versus actual greenhouse gas emissions. Environmental Research Letters, 2012. 7(4).

9.    Stephenson, T., J.E. Valle, and X. Riera-Palou, Modeling the Relative GHG Emissions of Conventional and Shale Gas Production. Environmental Science & Technology, 2011. 45(24): p. 10757-10764.

10.  Hultman, N., D. Rebois, M. Scholten, and C. Ramig, The greenhouse impact of unconventional gas for electricity generation. Environmental Research Letters, 2011. 6(4).

11.  Burnham, A., J. Han, C.E. Clark, M. Wang, J.B. Dunn, and I. Palou-Rivera, Life-Cycle Greenhouse Gas Emissions of Shale Gas, Natural Gas, Coal, and Petroleum. Environmental Science & Technology, 2012. 46(2): p. 619-627.

12.  Burnham, A., Life-Cycle Greenhouse Gas Emissions of Shale Gas, Natural Gas, Coal, and Petroleum (vol 46, pg 619, 2012). Environmental Science & Technology, 2012. 46(4): p. 2482-2482.

13.  Weber, C.L. and C. Clavin, Life Cycle Carbon Footprint of Shale Gas: Review of Evidence and Implications. Environmental Science & Technology, 2012. 46(11): p. 5688-5695.

14.  Wigley, T.M.L., Coal to gas: the influence of methane leakage. Climatic Change, 2011. 108(3): p. 601-608.

15.  Alvarez, R.A., S.W. Pacala, J.J. Winebrake, W.L. Chameides, and S.P. Hamburg, Greater focus needed on methane leakage from natural gas infrastructure. Proceedings of the National Academy of Sciences of the United States of America, 2012. 109(17): p. 6435-6440.

16.  Tollefson, J., Methane leaks erode green credentials of natural gas. Nature, 2013. 493(7430): p. 12-12.

17.  Levi, M.A., Comment on "Hydrocarbon emissions characterization in the Colorado Front Range: A pilot study" by Gabrielle Petron et al. Journal of Geophysical Research-Atmospheres, 2012. 117.

18.  Pétron, G., G.J. Frost, M.K. Trainer, B.R. Miller, E.J. Dlugokencky, and P. Tans, Reply to comment on “Hydrocarbon emissions characterization in the Colorado Front Range—A pilot study” by Michael A. Levi. Journal of Geophysical Research: Atmospheres, 2013. 118(1): p. 236-242.

19.  Logan, J., G. Heath, J. Macknick, E. Paranhos, W. Boyd, and K. Carlson, Natural Gas and the Transformation of the U.S. Energy Sector: Electricity, 2012. p. Medium: ED; Size: 255 pp.

20.  Yusuf, R.O., Z.Z. Noor, A.H. Abba, M.A. Abu Hassan, and M.F.M. Din, Methane emission by sectors: A comprehensive review of emission sources and mitigation methods. Renewable & Sustainable Energy Reviews, 2012. 16(7): p. 5059-5070.

21.  Simpson, I.J., M.P. Sulbaek Andersen, S. Meinardi, L. Bruhwiler, N.J. Blake, D. Helmig, F.S. Rowland, and D.R. Blake, Long-term decline of global atmospheric ethane concentrations and implications for methane. Nature, 2012. 488(7412): p. 490-494.

22.  Phillips, N.G., R. Ackley, E.R. Crosson, A. Down, L.R. Hutyra, M. Brondfield, J.D. Karr, K.G. Zhao, and R.B. Jackson, Mapping urban pipeline leaks: Methane leaks across Boston. Environmental Pollution, 2013. 173: p. 1-4.

23.  Stephenson, E., A. Doukas, and K. Shaw, Greenwashing gas: Might a 'transition fuel' label legitimize carbon-intensive natural gas development? Energy Policy, 2012. 46: p. 452-459.

Posted by gws on Wednesday, 27 March, 2013

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