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In this guest post for the blog Dot Earth, Lawrence Cathles, a professor of earth and
atmospheric science at Cornell, adds...
take. Since methane leakage from natural gas systems represents only 29 percent of the total U.S.
leakage (59 percent is f...
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A Fresh Defense of the Climate Benefits of Moving from Coal to Natural Gas


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Lawrence Cathles, an earth and atmospheric scientist at Cornell, has joined in a discussion of the climate benefits of a shift from coal to natural gas. The piece was written as part of a continuing discussion on Dot Earth of natural gas in the context of climate change:

Cathles's piece is a response to this New York Times Op-Ed article by Anthony Ingraffea, also a Cornell professor: "Gangplank to a Warm Future"

Published in: News & Politics
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A Fresh Defense of the Climate Benefits of Moving from Coal to Natural Gas

  1. 1. In this guest post for the blog Dot Earth, Lawrence Cathles, a professor of earth and atmospheric science at Cornell, adds this argument to others pointing to a substantial climate benefit in a shift from coal to natural gas: In a July 28 Op-Ed article in The New York Times, Cornell Professor Anthony Ingraffea reiterated his previously widely criticized message that natural gas is not a bridge to a low carbon energy future because it leaks. Previous comments to Dot Earth by Derry, Pierrehumbert and Muller refuted his arguments again by pointing out, respectively, that:  methane increases measured in the atmosphere attributable to unconventional gas leakage can force less than 1 percent of the warming of that simultaneously measured CO2 increases can,  sidestepping the reversible nature of methane leakage compared to the near permanence of CO2 accumulation is deceptive and irresponsible, and  stating that methane is a greenhouse gas 25 times more potent than CO2 is incorrect when the issue is leakage, the comparison is to coal, and the proper comparative potency is 3.3. To these points I would add that:  the substitution of gas for coal has clear warming benefits even when considered within the short term global warming potential framework used by Robert Howarth and Ingraffea, and  from a resource availability perspective, coal poses the overwhelmingly dominant warming risk. All agree that the comparative impact of methane depends on the leakage rate, electrical conversion efficiency, and the time interval considered. Figure 1 is constructed using the same methods and similar parameters as used by Howarth, Ingraffea and Santoro in their 2011 paper in Climatic Change where they first stated that gas could be twice as bad as coal. The figure shows the crossover leakage at which methane is as bad as coal in the short (20 year) and long (100 year) term when coal electrical plants with a range of electrical conversion efficiencies (ece) are converted to gas plants with 60 percent ece. If the time frame is 20 years, and the ece of both the coal and gas plants is 60 percent, the cross-over is at a gas leakage of 2.8 percent of production. If the coal plant replaced has a 40 percent ece, the cross-over is at 5.4 percent. For leakages less than this, substitution of gas for coal will reduced greenhouse warming. Initially the coal plants replaced will be the oldest and most inefficient, and coal plants probably can never have conversion efficiencies as high as 60 percent so the last case is the most relevant at least initially. According to E.P.A. report 430-R-13-01, the methane leakage associated with gas production since 1990 has been less than 2.5 percent, and since 2007 has declined quite sharply, to 1.7 percent in 2011. Thus, by Ingraffea’s own methods, substitution of coal for gas will reduce global warming and move the world away from any tipping points, even on a 20 year timeframe. Even if “the next two decades are crucial,” substituting gas for coal is one of the best steps we could Figure 1. Benefit of substituting gas for coal. If leakage is below lines, substitution will reduce greenhouse warming.
  2. 2. take. Since methane leakage from natural gas systems represents only 29 percent of the total U.S. leakage (59 percent is from enteric fermentation, landfills, and manure management, according to the E.P.A. report cited above), we can look to many places other than gas production to reduce methane leakage if it is of concern. My second point is that, from a resource abundance perspective, coal is the fossil fuel to avoid or minimize. Measured in terms of the number of pre-industrial atmospheres worth of CO2 (PAL) that burning the resource base (the resource that could be feasibly ever recovered) could add to the atmosphere, and using the generous resource base estimates of Rogner (Ann. Rev. Energy and Env., 22, 1997, p217), natural gas could add 0.9 PAL, oil 1.2 PAL, and coal 6.6 PAL. Burning all the imaginable oil and gas could (if no CO2 were removed) thus increases the atmospheric content of CO2 around twofold, whereas burning all the coal would increase it 6.6 fold. We would be wise to minimize our eventual consumption of the world’s coal resources. Here a second aspect of Rogner’s analysis is important: Rogner emphasizes that once extraction of a resource begins, technological advances tend to keep the cost of its extraction relatively constant until the resource base is exhausted. This means that if China and India decide to recover coal and build big coal industries, their coal resources will likely be fully extracted. But if they focus first on natural gas (which also has immense pollution, health, and safety advantages) the gas resource will be exhausted with comparatively little harm, perhaps giving clean energy sources time to eliminate the desirability of utilizing coal while most of its resource base still remains untapped. We should do everything we can to encourage developing countries to use natural gas first and in preference to coal. It is not what we do, but what they do, that will count most for global warming. Making natural gas scary will not help. Elaboration of these points and the spreadsheet used to calculate Fig. 1 can be found at . Lawrence M. Cathles August 16, 2013 Professor of Earth and Atmospheric Sciences Cornell University Ithaca, New York 14853