Cornell Crosstalk: Dueling Groups of Cornell Profs add Heat but Little Light to Natural Gas Fracking Debate
Posted January 23, 2012 in Solving Global Warming
Last Thursday two groups of Cornell professors fired dueling press releases across the gorges of Ithaca. Lawrence Cathles and colleagues released a summary of their commentary rejecting claims by Robert Howarth and colleagues that using natural gas produced through hydraulic fracturing (“fracking”) results in more global warming than using coal. That was the conclusion of a report last April by Howarth et al, and on Thursday they shot back with a response standing by their original conclusion. Both commentaries are expected to be published in Climatic Change Letters later this year.
Unfortunately, these dueling critiques don’t add any real information to the debate. So, I’m sticking by my conclusion as stated in my post on the original Howarth study:
… NRDC has long advocated that energy efficiency and renewables should be our first choice, rather than gas or coal, because they are the fastest, cheapest and cleanest solutions to global warming. Howarth’s analysis certainly underscores that priority.
Ultimately, we need to move away from dirty fossil fuels altogether and transition to sources such as wind and solar that can’t leak, spill, pollute the air or run out. Until we get there, natural gas will play a role in our energy mix (but not a dominant one) and that's why it's so crucial for the industry to clean up its act.
Second, we need much better data about methane emission rates [from natural gas production] before firm conclusions can be reached about the climate impact of natural gas relative to coal. The good news here is that companies are now required to measure and report on these emissions, so we will have more accurate data in the years to come.
More importantly, we need stronger regulation of natural gas upstream operations to address the full array of harmful impacts from inadequately regulated production, including requirements for the use of best practices to minimize releases of methane and other contaminants.
Returning to yesterday’s releases, Cathles et al. raise three objections to Howarth et al.’s analysis: 1) Howarth et al. fail to account for the higher efficiency of natural gas power plants compared to coal plants; 2) Howarth et al. use too high of a global warming potential to convert methane emissions into carbon dioxide equivalent global warming impacts; and 3) Howarth et al. assume implausibly high methane leak rates from natural gas production, particularly gas production using fracking.
I discussed each of these issues in my previous post. Let’s review and see if anything new has been brought to light by the latest round of debate.
- Electricity generation efficiency. There are no new arguments here and I continue to believe that efficiency needs to be taken into account. Howarth et al. counter that most natural gas isn’t used to produce electricity. True. The largest share is used to heat homes and offices. Going back to burning coal for that purpose would be both much less efficient and disastrous for public health. Just ask anyone who has visited China in winter.
- Global Warming Potential. Again, there are no new arguments here. I discussed this issue at some length in my previous post so I will just reiterate here that there is no single right answer. A range of time frames needs to be considered. We can’t limit our time horizon to only 20 years when focused on methane emissions and then argue for looking out 100 years when considering carbon dioxide.
- Methane leak rate. This is the heart of the matter and there is a little bit new to say about it. Cathles et al. argue that no business in its right mind would allow 7.9% of its product to leak away when it has the capability to prevent it. Howarth et al. respond that at low natural gas prices it just isn’t profitable to plug the leaks, and natural gas prices are in fact really low right now. Howarth et al. provide a useful set of new references in Table 1 of their new commentary. While Howarth et al. argue on the basis of these references that “most studies conclude that methane emissions from shale gas are far higher than from conventional gas” the table also shows that the highest estimate from the other studies is at the low end of the range given in the original Howarth et al. paper. The only way to settle this issue is for industry to report comprehensively on its actual emissions, rather than fighting requirements to do so. This is important because only at the higher end of the range is the global warming advantage of natural gas seriously in question, as I will discuss next for those who want to dig further into the analysis.
As they say on APM’s Marketplace, let’s do the numbers.
Rather than make another attempt to provide a best estimate of the overall global warming impact of electricity from gas versus coal, let’s ask the question another way. For a central estimate of the methane leak rate, how high would the global warming potential of methane versus carbon dioxide have to be to wipe out the advantage natural gas has at the power plant? The answer is very high. I come up with 107. That’s more than four times the GWP adopted by the international climate treaty and three times the highest GWP proposed for a 100 year time horizon. It’s even slightly higher than 20-year GWP favored by Howarth et al. Only a very short term focus (by climate system standards) can justify a GWP this high. (My calculations are based on EPA’s estimate for the methane leak rate (0.6 gC/MJ), which is the highest number in Howarth et al’s table other than the high end of their own range. I took emission factors for coal and gas combustion directly from EPA and assumed a 50% and 33% generation efficiency for natural gas and coal power plants, respectively).
We could also ask the question a different way: For a middle ground estimate for the global warming potential how high would the methane leak rate have to be to wipe out the advantage natural gas has at the power plant? Again the answer is very high. I argued in my original post on this subject that a middle ground GWP might be 42-56. Let’s take 50 as a nice round number. Then using the same assumptions on emission factors and efficiency, the methane leak rate would have to be more than 8% of production (1.3 gC/MJ), which is a little above Howarth et al.’s high end estimate and more than twice EPA’s estimate.
At the end of the day my hope is that this debate between academics becomes an academic debate. We can and must phase out the use of fossil fuels, and in the meantime we can and must reduce methane leak rates from whatever they are at present to well below one percent. That’s the way to protect our health in both the near and the long term.
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