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Why Methane Doesn’t Matter*

by Michael Levi
September 14, 2011

Methane emissions from natural gas extraction have been getting a lot of attention in recent months. The latest contribution is a forthcoming paper in Climatic Change by Tom Wigley and colleagues at NCAR that has been attracting considerable attention. It models a scenario in which much of the world’s coal consumption is replaced by gas and finds that near term temperatures increase a little bit while longer term temperatures (beyond a few decades) are only slightly lower (see the figure below). It thus concludes, as several others have, that replacing coal with gas is at best a waste of time, and potentially even bad.

 

 

 

 

 

 

 

 

 

 

 

 

I’ll have more to say about the broader question of gas as a bridge fuel in a later post – I’ll just note for now that my views are becoming much more nuanced as I dig deeper into the matter. In this post, I want to make a simpler point: if you’re focused on limiting climate change to the sorts of targets that are typically discussed (such as two degrees centigrade over preindustrial levels), then worrying about methane from gas production is largely a waste of your time.

 

Here’s why. Let’s assume, consistent with most policy discussions, that you’re aiming to keep carbon dioxide concentrations below 450 ppm and temperature rises to below two degrees. (Yes, these two have only a loose probabilistic relationship with each other, but they’re what policymakers and analysts generally use to frame their thinking.) You’re pretty much going to have to wipe out the use of coal without CCS by mid-century. Indeed you’ll also have to get rid of (or at least severely slim down on) most traditional natural gas consumption too.

 

That means that any talk of natural gas as part of a 450 ppm program needs to look at it as a genuine “bridge fuel” – something that ramps up in the near term before giving way to zero-carbon options by around 2050 or so. This article about the MIT Future of Natural Gas study does a nice job of explaining that.

 

This has big implications. The effects of methane on the climate are relatively short lived. (Methane has an atmospheric lifetime of about a dozen years.) If increased natural gas production leads to substantially larger methane emissions in the next decade or two, but natural gas is then ramped down as part of a “bridge fuel” strategy, the effects won’t linger long. Indeed they should be expected to mostly vanish within a couple decades of the bridge’s end. [UPDATE: For clarity, I should note that methane is ultimately transformed into carbon dioxide in the atmosphere. But the impact is small. For each one percent of produced natural gas that leaks as methane, that will ultimately add only one percent to the CO2 impact of gas use in the atmosphere.]

 

Many will instinctively dismiss this as irrelevant to the challenge at hand – after all, if we face tipping points in the earth’s climate much sooner than mid-century, it would seem imprudent to push up temperatures during that time. But here’s the thing: if we’re going to cross a tipping point for temperatures in the next few decades, methane emissions from natural gas production won’t be the difference. Temperatures are already heading inexorably up because of built up intertia in the climate system and some unavoidable emissions from existing energy infrastructure. They will continue to rise over the next century even with heroic efforts to rein in emissions. An extra twentieth of a degree of warming from the replacement of gas with coal (that’s the bump in the Wigley et al paper) won’t put us over any thresholds that we weren’t already going to cross a few years later. Moreover, by the time we get to peak global temperatures – in 2100 or so even in a world with massive greenhouse gas reductions and stabilization at two degrees – the lingering effects of methane won’t be around to push temperatures even higher. (The same cannot be said, by the way, for the carbon dioxide emissions from either coal or gas, though an analogue does apply to the case of sulfur dioxide pollution from coal fired plants, which figures prominently in Wigley et al.)

 

Ultimately, I’m fairly confident in saying that if you’re focused on the sorts of climate objectives that most policymakers talk about, you ought not worry much about the methane emissions from increased use of natural gas. A few caveats, though. First, this is not an argument against worrying about methane in general. (Hence the asterisk on the title of this post.) Persistent emissions of methane lead to persistently elevated methane concentrations and hence to sustained higher temperatures. Reducing those methane emissions matters. But emissions from gas production as part of a bridge fuel strategy don’t fall in that category, since their effects won’t be around when they might really matter. (Emissions from gas production as part of a longer term strategy involving gas with CCS might matter. If we get to a point where CCS use is widespread, though, I’m going to assume that people are also cleaning up their gas production operations.) Second, this does not mean that gas is necessarily a fantastic bridge fuel – it simply does away with one objection to the increased use of gas. (I’ll have more to say about the broader question another time.) Third, I’m not entirely convinced that the argument I’ve just made works if your goal is, say, 550 ppm or higher; I’ll have to spend some more time thinking about that. I suspect, though, that it still holds up.

Post a Comment 6 Comments

  • Posted by David B. Benson

    All sources of so-called greenhouse gases matter. As all are well mixed in the atmosphere (taking about 2 years) the origin is irrelevant in determining the excess warming produced.

    Methane is only a bit more complex in that it eventually is transformed into carbon dioxide with a different global warming potential per carbon unit.

    [ML: Take a look at the numbers. This effect is pretty tiny compared to the CO2 emissions from burning the methane.]

  • Posted by Scott

    Yes…..but your article needs clarity to not come off as sensational. First, the title. Should be Methane from natural gas drilling doesn’t matter. Because capturing methane from landfills clearly does matter….especially when it produces clean energy. Second….should consider that this is an American perspective. Several other gas drilling ops in other countries really do offset carbon intensive fuels….as well as high sulphur (pm) diesel in transportation, etc. Third, your use of the 450ppm CO2e target should be clarified for the American audience…..ie why you are not using 350ppm CO2 (ref for you below).
    Ackerman, Frank, Elizabeth A. Stanton, Stephen J. DeCanio, Eban Goodstein, Richard B. Howarth, Richard B. Norgaard, Catherine S. Norman, and Kristen A. Sheeran, 2009.
    “The Economics of 350: The Benefits and Costs of Climate Stabilization.” Economics for Equity and the Environment.

    Hansen, J., M. Sato, P. Kharecha, D. Beerling, R. Berner, V. Masson-Delmotte, M. Pagnani, M. Raymo, D. L. Royer and J. C. Zachos, 2008. “Target atmospheric CO2: Where should humanity aim?” The Open Atmospheric Science Journal 2: 217-231.

    Hoffert, Martin I., Ken Caldeira, Atul K. Jain, Erik F. Haites, L.D. Danny Harvey, Seth D. Potter, Michael E. Schlesinger, Stephen H. Schneider, Robert G. Watts, Tom M. L. Wigley, and Donald J. Wuebbles, 1998. “Energy implications of future stabilization of atmospheric CO2 content,” Nature 395: 881-884.

  • Posted by Miguelito

    I’ve posted this elsewhere because this study is getting widely cited, but it isn’t nearly as good as it’s being portrayed to be. Namely, it does a very poor job of depicting a carbon-policy future and uses gas simply as a replacement fuel rather than a bridge fuel.

    If you look at what Wigley has done, he starts with non-policy scenario of increased coal usage out to about 2110 (quadrupling the burning of coal), before the overall burning of coal beings to decrease (kind of like peak coal). That’s reasonable for a non-carbon policy future.

    Then, to model fuel-switching, he starts switching gas with coal such that gas replaces 50% of coal burning by 2050 and no more after that. Ultimately, gas-use quadruples by 2110. Coal use still manages to double by then (less of it being used, but it’s still growing, especially if gas use is capped at 50% at 2050).

    Well, of course, if we quadruple gas use by 2110 and double coal use, there are probably going to be GHG issues. As stated before, he’s treating gas as a replacement fuel and not a bridge fuel. He also doesn’t include any coal being switched with other sources of energy like solar, wind, hydro, etc… Remember: fuel switching is not going to occur in a policy vacuum, but where other, much cleaner fuels will also be used to take coal out of the fuel mix. And it’s this total fuel mix we need to know the emissions of.

    As for the use of leakages up to 10%, the money shot: “The most important result, however, in accord with the above authors, 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.”

    The reality is that it’s easy to keep emissions below 2% (things might be about 2% or a little above right now) if some simple regulations are applied: 1) green completions are mandatory (and, if green completions are not possible, the flowback gas must be flared); and 2) older pipelines and older gas-processing plants must be retrofitted with new gear to reduce leaks, something that can be easily done for low cost and with existing technology. And, the regulations would earn producers and pipeline companies revenue, partially offsetting costs to earning a profit in the long run.

    So, the conclusions aren’t very reliable unless people were seriously considering burning that much coal and gas that far into the future, which I hope policy makers weren’t. Even then, if we keep methane leaks low, it also shows that the gas strategy might work even in a relatively pessimistic scenario of the fuel mix.

  • Posted by Giovania

    The conclusions of this study are calculated based on average methane leakage from production, but the larger concern by local residents is the methane leaking on stream and river banks, water wells, shallow creeks, and other unmonitored, non-production sources. There have been dozens of reports on new sites of methane bubbling out of these places across the nation since drilling commenced in their area. In the Susquehanna River, for example, water-side residents continue to find new sources of bubbling along the river since hydrofracking began to expand in the area. Sure, it can be controversial to pinpoint these leaks directly to drilling, but shouldn’t it be a concern that these leaks occur in conjunction to drilling in proximity to the site? We are sticking thousands of giant vertical and horizontal drills, shooting hundreds of chemicals and millions of gallons of water and sand, and creating little fissures and cracks all over the landscape to release methane…

    Lighting the creek in your backyard on fire can be fun I guess, but on the larger scope, how is this impacting water and air quality; how is this impacting our family and children’s health and future?

  • Posted by David B. Benson

    From
    http://unfccc.int/ghg_data/items/3825.php
    the global warming potential of methane at the 100 year time horizon is 21. So if 5% escapes the total is

    0.05×21 + 0.95×1 = 2.00

    exactly double the global warming potential of actually burning 100% of the methane.

    [ML: There is a good reason why careful analyses don't use GWPs. That 2.0 figure is mostly due to warming in the first 10-20 years.]

  • Posted by David B. Benson

    Fine. From the same reference the BWP for methane at the 20 year horizon is 56. Now that 5% methane leak really shows up.

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