35 Responses to New study questions shale gas as a bridge fuel
Leakage of methane from fracking boosts shale gas global warming impact; National Academy review is warranted
Comparison of greenhouse gas emissions from shale gas (with low and high estimates of fugitive methane emissions) [with other energy sources]. 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 as described in the text (pink bars).
I was a (relatively) early booster of shale gas as a potential game changer for greenhouse gas mitigation [see Game Changer, Part 1: There appears to be a lot more natural gas than previously thought (6/10) and Part 2: “Unconventional gas makes the 2020 climate targets so damn easy and cheap to meet” (7/10)].
But there were always lurking concerns about the impact of methane leakage in from the unconventional gas extraction process known as hydraulic fracturing, since methane is a considerably more potent greenhouse gas (GHG) than carbon dioxide. Now three Cornell University professors have published a major analysis in Climatic Change, “Methane and the Greenhouse-Gas Footprint of Natural Gas from Shale Formations,” that seeks to quantify the impact of the leakage from the best available data.
They find a leakage rate large enough to seriously undercut gas’s GHG benefit even in high-efficiency combined cycle plants — and one that is all-but-fatal to any GHG benefit from using natural gas as a transport fuel. That conclusions is doubly true if one looks at the GHG impact over a few decades, rather than a century.
This is a potentially game-unchanging conclusion for one of the seminal energy policy choices of this decade — how hard to push shale gas here and around the world. And yet, as the lead author Cornell Prof. Robert Howarth explained to me in an interview, it is based upon very limited data. And that’s in part because the industry has fought efforts to get more data. Prof. Howarth agreed with my suggestion that this would be a very ripe topic for the National Academy of Sciences to review.
The study’s basic conclusion is that shale gas production is a bigger, longer and more complicated enterprise than conventional drilling, and that methane leakage is much higher during production and processing:
Natural gas is composed largely of methane, and 3.6% to 7.9% of the methane from shale-gas production escapes to the atmosphere in venting and leaks over the life- time of a well. These methane emissions are at least 30% more than and perhaps more than twice as great as those from conventional gas. The higher emissions from shale gas occur at the time wells are hydraulically fractured””as methane escapes from flow-back return fluids””and during drill out following the fracturing. Methane is a powerful greenhouse gas, with a global warming potential that is far greater than that of carbon dioxide, particularly over the time horizon of the first few decades following emission.
The authors argue that the urgency of climate change necessitates looking at shorter time horizons than 100 years :
Methane is a far more potent GHG than is CO2, but methane also has a tenfold shorter residence time in the atmosphere, so its effect on global warming attenuates more rapidly (IPCC 2007). Consequently, to compare the global warming potential of methane and CO2 requires a specific time horizon. We follow Lelieveld et al. (2005) and present analyses for both 20-year and 100-year time horizons. Though the 100-year horizon is commonly used, we agree with Nisbet et al. (2000) that the 20-year horizon is critical, given the need to reduce global warming in coming decades (IPCC 2007). We use recently modeled values for the global warming potential [GWP] of methane compared to CO2: 105 and 33 on a mass-to-mass basis for 20 and 100 years, respectively, with an uncertainty of plus or minus 23% (Shindell et al. 2009). These are somewhat higher than those presented in the 4th assessment report of the IPCC (2007), but better account for the interaction of methane with aerosols.
Here is Shindell et al., “Improved Attribution of Climate Forcing to Emissions” (subs. req’d). Climate scientists I’ve spoken to think it is reasonable to use Shindell’s numbers.
Putting the leakage and the GWP together results in the figure reprinted at the top. Here is an hour-long video that explains everything you could want to know about the study:
Of course, gas can be burned much more efficiently than coal, in combined cycle plants. The authors’ supplementary material notes:
… our estimate of GHG footprint of fuels does not include the efficiency of final use. If we examine electricity production, current power plants in the US are 30% to 37% efficient if powered by coal and 28% to 58% if powered by natural gas…
When viewed on the 20-year time horizon, the GHG footprint for producing electricity from shale gas is 15% less than that for coal, when we assume the lowest methane emissions and highest efficiency of use for producing electricity. However, at the high-end estimates for methane emissions the GHG footprint is 43% higher than that for coal even when burned at high efficiency.
So, should we consider a 20-year time horizon or 100?
Prof. Howarth, who chairs the International SCOPE Biofuels Project and was Editor-in-Chief of the journal Biogeochemistry from 1983 to 2004, made a compelling case to me: “If you believe climate change is real and that we are approaching tipping points, then you need to look at a time horizon of a few decades” for assessing impact.
Obviously, those who read the scientific literature know that climate change is real and that we are approaching tipping points (see for instance NSIDC bombshell: Thawing permafrost feedback will turn Arctic from carbon sink to source in the 2020s, releasing 100 billion tons of carbon by 2100).
After all, we are talking about potentially investing many tens of billions of dollars in a new generation of natural gas-fired plants. If the net benefit compared to coal is small over the key time frame of a few decades, the investment may not make sense from the perspective of cost per ton of CO2eq (equivalent) reduced.
And we need to look even closer at major investments in switching to natural gas vehicles, as the study notes:
Further, natural gas is often viewed as a replacement for diesel and gasoline as a transportation fuel and a replacement for fuel oil for space heating. In these roles, natural gas has no advantage with regard to efficiency of use.
Not only does natural gas have no advantage with regard to efficiency, but the carbon intensity of diesel is considerably lower than that of coal. In other words, there was always only going to be a small GHG benefit in switching to natural gas vehicles. This study would seem to suggest at the very least that we can no longer confidently assert there is any greenhouse gas benefit at all from such a shift.
Note: Diesel fuel does emit black carbon which also has potent short-term warming effect. Howarth et al d not factor that into their calculation. Of course, the BC also undercuts the advantage of diesel over gasoline, too, which is hardly ever discussed. That said, diesel particulate filters (DPF) “installed in place of a traditional muffler [would] reduce diesel PM emissions by 90%.” But I digress.
Given the bombshell nature of the conclusions, I asked Howarth what his confidence was in the results. He is very clear that this is “poorly documented information” and that we “did our best with sparse data.” Why is the data sparse?
As Mother Jones’ Kate Sheppard explains
That’s because industry isn’t currently required to report their emissions””and in fact are one of several industries suing the Environmental Protection Agency to keep it that way. Getting the data proved to be “amazingly frustrating,” [Howarth] says. The numbers he and his coauthors used in the study were drawn from a combination of industry reports, presentations, and dated EPA estimates.
Getting these numbers right should be a top priority, which is why I suggest a National Academy of Sciences review. Howarth said he’d “be delighted” with such a review. It may also require some serious push in the executive branch to get better data.
One obvious question: Can fugitive or leaked emissions be reduced? The study addresses that question directly in a short section:
Can methane emissions be reduced?
The EPA estimates that ‘green’ technologies can reduce gas-industry methane emis- sions by 40% (GAO 2010). For instance, liquid-unloading emissions can be greatly reduced with plunger lifts (EPA 2006; GAO 2010); industry reports a 99% venting reduction in the San Juan basin with the use of smart-automated plunger lifts (GAO 2010). Use of flash-tank separators or vapor recovery units can reduce dehydrator emissions by 90% (Fernandez et al. 2005).
Note, however, that our lower range of estimates for 3 out of the 5 sources as shown in Table 2 already reflect the use of best technology: 0.3% lower-end estimate for routine venting and leaks at well sites (GAO 2010), 0% lower-end estimate for emissions during liquid unloading, and 0% during processing.
Methane emissions during the flow-back period in theory can be reduced by up to 90% through Reduced Emission Completions technologies, or REC (EPA 2010). However, REC technologies require that pipelines to the well are in place prior to completion, which is not always possible in emerging development areas. In any event, these technologies are currently not in wide use (EPA 2010).
If emissions during transmission, storage, and distribution are at the high end of our estimate (3.6%; Table 2), these could probably be reduced through use of better storage tanks and compressors and through improved monitoring for leaks. Industry has shown little interest in making the investments needed to reduce these emission sources, however (Percival 2010).
Better regulation can help push industry towards reduced emissions. In reconciling a wide range of emissions, the GAO (2010) noted that lower emissions in the Piceance basin in Colorado relative to the Uinta basin in Utah are largely due to a higher use of low-bleed pneumatics in the former due to stricter state regulations.
One climate scientist said of his take away: “Bottom line? Shale gas is not going to save the world, but if well managed/regulated it is marginally better than coal and oil for climate.”
The problem, of course, is that we have no evidence that shale gas is well-managed, and we know for a fact that it is not well regulated (see the CAP report, “Drilling down on natural gas fracking concerns“).
I also question whether we have any evidence it is better than oil for transportation since, as noted, you don’t get the big efficiency gain from natural gas vehicles that you can get from replacing existing coal plants with new, high-efficiency natural gas plants.
Finally, it bears repeating we have only a short time frame to sharply reduce GHGs before it becomes all but impossible to avoid key thresholds and tipping points — particularly the amplifying carbon-cycle feedbacks (discussed here). And that means we can’t afford to spend lots of money on something that is “marginally better” than what we are doing today.