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Natural Gas: A Better "Climate" Fossil Fuel?

By Chip Knappenberger -- April 29, 2011

When it comes to climate, are all fossil fuels equal?

“No,” the answer has been until very recently. In terms of how much carbon dioxide (the major force behind the human alteration of the atmospheric greenhouse effect) is produced when burning various fossil fuels to produce a unit amount of energy, there is a definite ranking. From the most CO2 produced to the least, the list goes coal worst, oil next worst, and natural gas least worst.

While it would be stretch to call natural gas the sweetheart of climate-change-fearing environmentalists, many have considered it to be the lesser of the reliable-energy-source evils. Of course, they rally behind the wind and the sun, but even renewable energy idealists understand that there needs to be a bridge between where we are now and where they would like us to be—and that bridge is envisioned to be constructed primarily from natural gas (a foundation furthered by the nuclear problems in Japan).

But a new study out of Cornell University makes the natural gas bridge out to be another Gallopin’ Gertie rather than a secure pathway to the future—at least when it comes to being a climate-change mitigator/savior.

The Climate Impact of Natural Gas

According to the carbon dioxide emissions factors given by the Energy Information Administration (which assume 100% combustion), coal burning emits on average about 95 kilograms (209 lbs) of carbon dioxide per million BTUs produced. Burning oil to produce a million BTUs of energy produces about 20kg less, or about 75 kg (165 lbs) of CO2. And burning natural gas to do the same thing saves you another 20kg, producing only about 55 kg (121 lbs) of carbon dioxide.

So, on the face of things, numbers like these are what make natural gas the darling of climate change mitigators. They see that a switch from coal to natural gas could cut global-warming CO2 emissions by more than 40%. This number falls quite a bit short of the long term goals of reducing greenhouse gas emissions by more than 80%, but nevertheless it is a big step in the right direction. Thus, natural gas is viewed as a “bridge” to a largely carbon-free energy production—that is, it is a construct which buys time for other technologies to mature and/or be developed.

One of the biggest drawbacks with using natural gas as a bridge fuel are doubts as to whether or not there exist ample supplies of natural gas to adequately serve the world’s growing power needs, while waiting for carbon-free energy technologies to become viable. It had seemed that the gas was in relatively short supply—that is, everywhere except in Russia—a situation much to the chagrin of Western Europe (and its attempts to reduce CO2 emissions as obligated under the Kyoto Protocol).

Along Comes Fracking

But all that changed in the last couple of years with the development of a method of hydraulic fracturing (“fracking”) of deep shale beds to release huge amounts of methane stored in the geologic formations. The fracking processes involves drilling deep vertical wells to reach the natural gas-rich shale beds, and then extending the wells horizontally through the layer of shale. A flow of water (mixed with a proprietary cocktail of other chemicals) is forced into the shale bed under very high pressure which fractures the shale thereby releasing natural gas which can then be collected through the well.

Fracking has the potential to open up huge domestic gas supplies and produce jobs. It has already done so in parts of Wyoming, Louisiana, Texas, and most notably, Pennsylvania where it has been estimated that the Marcellus Shale formation which underlies a large portion of the western half of the state can produce enough natural gas to supply the U.S. needs for two decades.

But, despite its potential to supply large amounts of low-CO2 producing energy, the enthusiasm for the rapid deployment of fracking technologies is not universally shared.

If you own the mineral rights over prime shale beds then you are ecstatic, because the potential cash flow is large. If you live atop (or near) those same shale beds and don’t own the mineral rights, then you probably fear any potential contamination of the water (both ground water and surface water) and increased heavy equipment traffic on previously quiet country roads (or course your outlook may change is you are a purveyor of goods and services that the gas miners may require such as hotel rooms, apartments, restaurants, bars, etc.).

And if you are like most of the rest of us—far removed from the local impacts (be they negative or positive), you are probably quite happy to have a new fuel source that is relatively inexpensive, apparently in high supply, non-radioactive, and produced in the good old U. S. of A. Throw in mitigating climate change, and it seems like you have the perfect fuel (less some local nuisances).

But now comes word that perhaps natural gas from fracking isn’t as good for the climate as has been postulated—and thus its inherent advantage over coal and oil isn’t as great as advertised.

The Howarth et al. Study

A new analysis that tracks the global warming potential of hydraulic fracturing has just been published by a group of researchers at Cornell University led by Dr. Robert Howarth and has this unexpected result:

“Compared to coal, the [greenhouse gas] footprint of shale gas is at least 20% greater and perhaps more than twice as great on the 20-year horizon and is comparable when compared over 100 years.”

Better read that again—the warming influence on the earth’s climate from shale gas is “perhaps more than twice as great” as that from coal, at least on the timescale of decades. And even after a century, the impacts may be equivalent.

If this result holds up, gone would be the inherent advantage of shale gas over coal. After all, coal is also a fuel source that is relatively inexpensive, apparently in high supply, non-radioactive, and produced in the good old U. S. of A.

But how can the Howarth et al. finding be true if burning natural gas produces only about half the carbon dioxide as does burning coal? Well, it seems the early stages of fracking operations releases a lot of methane—the primary constituent of natural gas and a greenhouse gas that is a more powerful warmer than is CO2.

On an equal mass basis, the “global warming potential” of methane has been calculated to be about 100 times that of carbon dioxide over a 20-year period, and about 33 times that of CO2 on a 100-yr period. The difference comes in because the atmospheric lifetime of methane is much shorter than that of CO2 as there are active scrubbing agents (primarily the hydroxyl radical (OH)) that act to break down methane in the atmosphere, and so an equal amount of methane stays in the atmosphere for a much shorter period of time than does carbon dioxide. But while it is there, methane is very good at trapping outgoing long-wave radiation that would otherwise escape directly to space.

According to Howarth et al., whose calculations are based on admittedly few available observations, a fairly high percentage (3.6% to 7.9%) of the total natural gas that is recovered from a fracking well is lost to the atmosphere. This “fugitive” methane escapes from the well during the initial stages of setting the well, fracturing the shale and removing the water/chemical mixture from the well.

When Howearth et al. add the greenhouse impact of this fugitive methane to the greenhouse impact of the carbon dioxide that is produced when the extracted natural gas is burned to produce energy, the total comes out to be about the same as the total greenhouse impact of burning coal to produce the equivalent amount of energy. This equivalence is calculated for a timescale of a century. When tallied over only 20 years, Howarth et al. find that the greenhouse footprint from natural gas produced from fracking exceeds that of coal by at least 20% and perhaps as much as 100%.

Figure 1. Comparison of greenhouse gas emissions from shale gas with low and high estimates of fugitive methane emissions, conventional natural gas with low and high estimates of fugitive methane emissions, surface-mined coal, deep-mined coal, and diesel oil. Top panel (a) is for a 20-year time horizon, and bottom panel (b) is for a 100-year time horizon. Estimates include direct emissions of CO2 during combustion (blue bars), indirect emissions of CO2 necessary to develop and use the energy source (red bars), and fugitive emissions of methane, converted to equivalent value of CO2 (pink bars). Emissions are normalized to the quantity of energy released at the time of combustion. (Source: Howarth et al., 2011).


Surely the Howarth et al. study is not the final word on this. And in fact, right out of the gate is has been met with a lot of resistance. Complaints have surfaced, among others, as to the true global warming potential of methane (Howarth et al. use values that are somewhat larger than reported by the IPCC), the reliability of the little actual data from fracking operations on which the conclusions were based, and whether the “fugitive” methane from the drilling operations actually escapes directly to the atmosphere or whether it is flared at the site (this turns out to make a big difference because if the methane is flared (i.e. burned), CO2 is released to the atmosphere rather than methane).

And, on top of this, since fugitive methane is lost profit, there should be financial incentives to keep it to a minimum (and improvements are anticipated as the fracking methodology matures). And if the market is deemed unsuccessful at reducing the direct methane loss, then in theory regulations could be applied.


At the very least, the Howarth et al. study is swaying the natural gas climate bridge a la Gallopin’ Gertie. Whether or not it suffers the same fate as Gertie and crumbles into the abyss only to be rebuilt with a different foundation and design, or whether it manages to stabilize itself and serve as a major pathway to a low(er) carbon future remains to be seen.

In any case, the Howarth et al. study should act to slow the civil war within the fossil fuel family (between natural gas and coal in electricity; natural gas and oil in transportation) while a more thorough examination of the potential climate impact of the full life-cycle of fossil fuels and their production methods are undertaken.

The climate playing field for fossil fuels is possibly a lot more level than it is generally considered to be.


Howarth, R. W., R. Santoro, and A. Ingraffea, 2011. Methane and greenhouse-gas footprint of natural gas from shale formations. Climatic Change, DOI 10.1007/s10584-011-0061-5, http://www.springerlink.com/content/e384226wr4160653/


  1. Jon Boone  

    Good explication of a complicated topic. Factoring all the variables, individually and in combination in a soup-to-nuts consideration, is a great equalizer–and a good way to compare the environmental impact of power technologies. Such comprehensive comparison by a few lonely but honest scientists showed a decade ago that corn ethanol likely increases greenhouse gas production. Similar analyses indicate that the total input required to manufacture electric vehicles may release as much or more greenhouse gasses than would be the case absent those vehicles. And this doesn’t account for rare earth mining practices.

    The Howarth, et al study is surely the first salvo in what should be many inquiries into the relative environmental consequences of natural gas vis a vis coal and oil–all high capacity producers with ongoing roles to play in the maintenance of modernity.


  2. JavalinaTex  

    Energy in Depth web site had an extensive analysis and rebuttal. I could not locate the exact link. They were quoted in the NY Times article around 4/12.


    One huge issue was that the Cornell study used “lost and unaccounted for gas” in a gathering system percentages as representative of fugitive emissions of methane to the atmosphere. Gas measurement of raw natural gas and other mixes of gases is notoriously inaccurate and will often systemically shows losses. Yet, actual physcal losses are likely very low. This is a much litigated issue. But the bottom line, is the researchers took an average and assumed it went to atmosphere.

    Apparently, the analysis did not explicitly compare coal vs. gas efficiency in electric generation. Their rationale was that natural gas is used for other uses (heating, chemical process, industry); however, most of these one would not use coal anyway. This was discussed in NY Times Blog about a week ago.

    I am also skeptical that coal methane emissions have ever been properly estimated; especially with surface mining. When one considers the prodigous coal bed methane production in the Powder River Basin, I really wonder if the emissions might not be orders of magnitude higher.

    There were also some huge assumptions made on methane losses in fracking, primarily because it was assumed the fracking would be completed before a ipeline is available. While this might be true in the early development, I would questoin whether this would be the case when they infill drill (typically, you have about six wells per square mile, and drill two square miles from one site; you at most wouldn’t have a pipeline for the first two wells, and in fact, producers are getting pretty agressive at having the pipelines in place ahead of time or also delaying fracking until months after drilling – as frack crews can be hard to obtain and they try to assembly line fracking in an area.

    Bottom line, we should all read the study and pick it apart, but it appears that it was done more to generate sound bites and for political gain (apparantly the author is also an activist against drilling) than to provide real valuable information.


  3. Roger Caiazza  

    To me the Cornell Study is a sophisticated “Not in my backyard” response. Cornell University is located smack dab in the middle of an area that has large potential shale gas potential. Currently the State has put a moratorium on drilling for shale gas until they develop regulations but when it starts ivory towers of Cornell will be inconvenienced. The training of the primary author of the study was in oceanography, and much of his research still focuses on coastal marine ecosystems. But he also works on freshwater systems (both rivers and lakes) and on large river basins. At all the local meetings on shale gas drilling he has been a prominent fixture. But as shown in this post, there are serious short-comings on the primary findings. Nonetheless the press releases have gone out and now opponents can say Cornell said shale gas is worse than coal.


  4. Chris T  

    Actually, coal does contain quite a few naturally occurring radioactive substances. The annual amount of radioactive material released by a normally operating coal plant is much higher than that released by a nuclear plant. Well below dangerous levels, but not nonexistent either.

    The study ignores the other benefits of NG: far fewer particulates, sulfer dioxide, and nitrous oxide.


  5. Ed Reid  

    In our “brave new world”, nothing but wind, solar, geothermal, OTEC and wave energy is acceptable. Resistance is futile! 🙂


  6. Energy and Environment News  

    […] Natural Gas: A Better “Climate” Fuel? Chip Knappenberger, MasterResource.org, 29 April 2011 […]


  7. Randy Taylor  

    Thanks for laying this out so well.

    I would suggest that it would have been helpful to cover the issue of natural gas cost and extent of drilling required, as well. Public statemetns by producers as well as analysts indicate that a producer price in the $7-9 range will be necessary to produce profits and the volumes needed. And a high speed treadmill of drilling to keep production growth ahead of rapid depletion.

    One question: what is your source for the “20 years supply” statistic on Marcellus gas, and please clarify I am correct in assuming this refers to resource, not reserve, and current rate of use.

    Thank you.


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