Climate Danger from Natural Gas

2012 February 8
by Chris Vernon

A couple of years ago I wrote a piece (Natural gas, the green choice?) for The Oil Drum looking at the climate change implications of using gas rather than coal. Burning gas to produce electricity produces only around 40% the CO2 emissions of burning coal. However, since methane (CH4) is itself a potent greenhouse gas, its release to the atmosphere without being burnt can quickly compensate for this CO2 advantage against coal. I included this chart to illustrate the point:

On the left, CO2 emissions per kWh for coal and natural gas. On the right, the global warming potential of leaked CH4 expressed as CO2

The key take-away was that if the natural gas leak rate is 3%, the global warming potential of a kilowatt-hour of electricity from gas is equivalent to coal. The details behind the chart are in the original article.

This week the journal Nature has an article (Air sampling reveals high emissions from gas field) presenting measurements from a gas field and suggesting that “Methane leaks during production may offset climate benefits of natural gas.”

Led by researchers at the National Oceanic and Atmospheric Administration (NOAA) and the University of Colorado, Boulder, the study estimates that natural-gas producers in an area known as the Denver-Julesburg Basin are losing about 4% of their gas to the atmosphere — not including additional losses in the pipeline and distribution system.

This figure of 4%, their range is 2.3–7.7% loss, with a best guess of 4%, is well inside the danger zone suggesting gas has similar, if not higher, climate impact as coal.

Most of the gas from this site is produced by “fracking”:

Most of the wells in the basin are drilled into ‘tight sand’ formations that require the same fracking technology being used in shale formations. This process involves injecting a slurry of water, chemicals and sand into wells at high pressure to fracture the rock and create veins that can carry trapped gas to the well. Afterwards, companies need to pump out the fracking fluids, releasing bubbles of dissolved gas as well as burps of early gas production. Companies typically vent these early gases into the atmosphere for up to a month or more until the well hits its full stride, at which point it is hooked up to a pipeline.

Gas is often described as the ‘cleaner’ choice, as a transitional energy source between coal and low-carbon renewables. Gas does burn without emitting the oxides of sulphur (SOx) and nitrogen (NOx), traces of mercury, selenium and arsenic, as well as the particulates associated with coal and doesn’t leave the non-combustible slag. Despite this it is increasingly unclear that gas has a significantly lower climate impact and the fracking process itself is not as clean as conventional gas extraction.

6 Responses leave one →
  1. February 9, 2012

    It looks like no fraccing operation is complete without a de-gassing system and a flare stack to burn off evolved methane (and other hydrocarbons).

  2. Doreen permalink
    April 17, 2012

    In your original article your reference to the greenhouse effect of methane is based on a concentration level in ppb (billion); on the other hand the emission percentages you quote are based on mass. But there’s a molecular ratio per unit mass of 1:2.75 between methane and carbon dioxide (the molecular weight ratio). The mass impact of methane is thus not 25 times that of carbon dioxide, but 9 times. This suggests leakage rates of 9 % would be serious, rather than 3%. And I do wonder if anyone has considered that methane is lighter than air, will therefore rise and cool, and thus it’s potential for energy release post photon trapping will reduce.

  3. Chris Vernon permalink*
    April 17, 2012

    Doreen, this is not the case on either points.

    Firstly, the Global Warming Potential of CH4 is 25 times that of CO2, relative to an equal mass of CO2 emissions as stated in the CDIAC reference.

    On the second point, the atmosphere is well mixed, not stratified by density. It is not the case that methane is lighter air and thus rises. If that were the case, CO2 being heavier than air, would form a suffocating layer at the bottom of the atmosphere.

  4. Doreen permalink
    April 19, 2012

    The GWP of a gas depends primarily on the concentration of molecules of a gas in the atmosphere, and indirectly on the mass of the gas through molar density. That follows from understanding the photon trapping of the molecular covalent bonds. The IPCC assessments of the GWP of the various gases is entirely based on concentrations, and indirectly on masses. The idea that a ton of CH4 should be 25 times more warming whilst containing 2.75 times fewer molecules than a ton of CO2 is quite ludicrous – the energy trap levels are simply not that different in energy content. For a single gas, doubling the mass in the atmosphere will double the concentration. But if you release equal masses of different gases such as to double the atmospheric molecular concentration of one, that will not double the atmospheric molecular concentration of the other because they have different molar densities.
    The only reason methane is seemingly higher in GWP is because it is at much lower concentrations in the atmoshere than CO2, and therefore a smaller concentration increment is required for doubling. Your slope of impact for increasing percentage emissions is linear. Did you forget the logarithmic relationship, or are we so low in concentration changes that the non-linearity is insifgnificant.
    You make no mention of the lifetime of methane in the atmosphere; it’s 12 years (partly due to escape from earth’s gravity!). If you constantly add methane to an exponentially depleting store you will attain equilibrium concentration after about 3 lifetimes. Since gas burning operations have continued for nearly 30 years on the present scale I doubt the impact of that activity is capable of much greater impact than the present. Indeed, that probably explains why methane atmospheric concentrations have saturated. I also doubt that the accidental escape of methane whilst fracking will be significant compared to the amounts of unburnt methane that escape due to incomplete combustion.
    Stratification of the various gases does occur, albeit this is practically non-existent for O2/N2 (too close in density). But yes, CO2 does puddle slightly towards the ground – modified by thermal agitation and land/ocean aborption/release. For that reason, you never use CO2 as an extinguishent underground or in basements. But methane does rise slowly through the atmosphere, if it’s not clobbered on the way by other oxidation/change processes. A rising, and thus cooling gas cannot release trapped photon energy as readily as a warmer gas.

  5. Doreen permalink
    April 20, 2012

    Perhaps another try?
    I burn 100 tons of methane in my gas fired power station. That produces 275 tons of carbon dioxide and X MWhrs of energy. But if I’d been burning coal my carbon dioxide emissions would have been 275*890/360 tons, i.e. 680 tons to produce the same X MWhrs of energy. That’s 405 more tons of carbon dioxide than the gas station. But if the leakge rate of the supply line to the gas station had been ~3 %, according to your graph, the GWP would be the same as the coal station. So a leakage of 3 tons of methane would balance out 405 tons of carbon dioxide . . .

    These may not be your calculations, but you don’t give your calculations.

    I think the disconnection here is that you’re assuming that all gas production is burnt in the production of electrical energy. It isn’t.

  6. Barbara Hutton permalink
    March 5, 2013

    Firstly, Doreen, you have the number of CH4 and CO2 molecules per ton the wrong way round. You say “The idea that a ton of CH4 should be 25 times more warming whilst containing 2.75 times fewer molecules than a ton of CO2 is quite ludicrous”.
    Quite so, a ton of CH4 has 2.75 times as many molecules as a ton of CO2, not the other way round.
    GWP is by mass measured in kg, not by mol. One kg of methane has 21 times the GWP of one kg of CO2, by definition. This is the definition used by the US EPA, IPCC and world meterological organisation.

    Secondly, Chris, by my calculations, on a molar basis, one molecule of CH4 has 7.6 times the radiative forcing potential of one molecule nof CO2. (Or about 9 times if you use a GWP of 25 for methane).

    Given that GWP is by kg, would that be correct for the ratio by mol?
    Does anyone have a reference on this?
    regards Barbara

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