Sunday, September 9, 2012

Bottom line: Does switching from coal to shale gas slow climate change?

Keith Kloor "asks" Will Fracking Help Or Hinder the Fight Against Climate Change? Unfortunately, it soon becomes clear that he has little interest in trying to answer that question, and instead uses it as an excuse to beat up on his favorite villains, those crazy environmentalists:
Gas emits much less carbon than coal (probably between 25% and 50% less), which is a net plus on the global warming ledger. And shale gas, in case you hadn’t heard, is entering a golden age; it is abundant and newly retrievable across the world, not just in the United States. It’s the bridge fuel to a clean energy future that liberal think tanks and university researchers were touting just a few years ago. Given the political stalemate on climate change, one energy expert gushed in a recent NYT op-ed: “Shale gas to the rescue.”

But a grassroots backlash to the relatively new technology (hydraulic fracturing) that unlocks shale gas has set in motion powerful forces opposed to this bridge getting built. Leading climate campaigners, citing concerns about industry practices and continued reliance on fossil fuels (even if less carbon intensive), are now a big part of the growing anti-fracking coalition. Mainstream environmentalists have also jumped on that bandwagon.
Thus the battle lines are drawn, with enviros and climate activists digging in their heels against a shale gas revolution that could pay big climate dividends.
Lest you think I'm quoting Kloor's conclusions following a careful analysis of the pros and cons of shale gas, the above is from the third, fourth, and fifth paragraphs of Kloor's essay. Really. So the title of the essay is really quite misleading. Kloor spends not a bit of virtual ink on whether fracking will "help or hinder the fight against climate change." Instead he blandly proclaims it "the bridge fuel to the clean energy future" and directs the remainder of his energies to the question of whether "enviros and climate activists" will help or hinder it.

It's a shame, and not just because it is rehash of an essay Kloor has written approximately five hundred times (Enviros crazy! Me sane and moderate!) dressed up as something new. It is a shame because the question itself is very interesting and important: is shale gas a good thing from the perspective of global warming, or not?

There are three major factors to examine in considering the relative impact of shale gas and coal on climate change:

1. CO2 produced per unit of energy.
2. Methane produced per unit of energy (conventionally referred to, with gas, as the methane leakage rate).
3. Aerosol cooling (coal more than gas, by far.)

Non-AGW factors will be left out of the equation for now. These include water pollution, direct harm from inhalation (asthma, COPD, lung cancer), and damage to the landscape. These are not unimportant, but they complicate an analysis that is already quite complicated. So we will stick with the effects on global warming.

Looking at the three factors above, we can see that the long-term factor (CO2) favors gas, while the short-term factors (methane and aerosols with their short half-lives in the atmosphere) favor coal. So we would expect, intuitively, that shale gas would do well in the long term, and less well in the short term. And this is exactly what the literature shows.

Looking at Hultman et al (2011) (4th abstract below) we see that methane leakage make shale gas worse than coal in the short term (20 years) about the same in the medium term (100 years) and better in the long term (500 years). Hultman et al does not consider the negative aerosol forcing associated with burning coal, so gas is relatively advantaged in these calculations.

When aerosols are included in the calculations, the break-even point for shale gas is even further in the future.

Here are a few of the recent papers examining this question:

We evaluate the greenhouse gas footprint of natural gas obtained by high-volume hydraulic fracturing from shale formations, focusing on methane emissions. 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. Methane contributes substantially to the greenhouse gas footprint of shale gas on shorter time scales, dominating it on a 20-year time horizon. The footprint for shale gas is greater than that for conventional gas or oil when viewed on any time horizon, but particularly so over 20 years. Compared to coal, the footprint of shale gas is at least 20% greater and perhaps more than twice as great on the 20-year horizon and is comparable when compared over 100 years. [Howarth et al became the focus of a debate between the authors and another group of researchers championed by Anthony Revkin. Cathles et al substituted optimistic estimates of methane leakage for Howarth's pessimistic estimates (which led to a letter, which led to a press release), and ignored the 20-year horizon, arguing that only 100 years and longer are appropriate measures of climate impact. Ignoring the 20-year time horizon is a common tactic of shale gas boosters, as we see below. Cathles goes further by ignoring the difference in aerosol forcing between present-day coal and shale gas, reasoning that we'll have to get rid of dirty coal plants someday anyway!]

"Greater focus needed on methane leakage from natural gas infrastructure"

Natural gas is seen by many as the future of American energy: a fuel that can provide energy independence and reduce greenhouse gas emissions in the process. However, there has also been confusion about the climate implications of increased use of natural gas for electric power and transportation. We propose and illustrate the use of technology warming potentials as a robust and transparent way to compare the cumulative radiative forcing created by alternative technologies fueled by natural gas and oil or coal by using the best available estimates of greenhouse gas emissions from each fuel cycle (i.e., production, transportation and use). We find that a shift to compressed natural gas vehicles from gasoline or diesel vehicles leads to greater radiative forcing of the climate for 80 or 280 yr, respectively, before beginning to produce benefits. Compressed natural gas vehicles could produce climate benefits on all time frames if the well-to-wheels CH4 leakage were capped at a level 45–70% below current estimates. By contrast, using natural gas instead of coal for electric power plants can reduce radiative forcing immediately, and reducing CH4 losses from the production and transportation of natural gas would produce even greater benefits. There is a need for the natural gas industry and science community to help obtain better emissions data and for increased efforts to reduce methane leakage in order to minimize the climate footprint of natural gas. 

Recent reports show growing reserves of unconventional gas are available and that there is an appetite from policy makers, industry, and others to better understand the GHG impact of exploiting reserves such as shale gas. There is little publicly available data comparing unconventional and conventional gas production. Existing studies rely on national inventories, but it is not generally possible to separate emissions from unconventional and conventional sources within these totals. Even if unconventional and conventional sites had been listed separately, it would not be possible to eliminate site-specific factors to compare gas production methods on an equal footing. To address this difficulty, the emissions of gas production have instead been modeled. In this way, parameters common to both methods of production can be held constant, while allowing those parameters which differentiate unconventional gas and conventional gas production to vary. The results are placed into the context of power generation, to give a ″well-to-wire″ (WtW) intensity. It was estimated that shale gas typically has a WtW emissions intensity about 1.8–2.4% higher than conventional gas, arising mainly from higher methane releases in well completion. Even using extreme assumptions, it was found that WtW emissions from shale gas need be no more than 15% higher than conventional gas if flaring or recovery measures are used. In all cases considered, the WtW emissions of shale gas powergen are significantly lower than those of coal.[Note, however, that this paper, brought to you by "Shell Global Solutions," ignores the 20-year horizon completely: "Some authors have considered 20-year global warming potential
factors, but use of these is not widely accepted."]

"The greenhouse impact of unconventional gas for electricity generation" Nathan Hultman, Dylan Rebois, Michael Scholten and Christopher Ramig 2011 Environ. Res. Lett.

 New techniques to extract natural gas from unconventional resources have become economically competitive over the past several years, leading to a rapid and largely unanticipated expansion in natural gas production. The US Energy Information Administration projects that unconventional gas will supply nearly half of US gas production by 2035. In addition, by significantly expanding and diversifying the gas supply internationally, the exploitation of new unconventional gas resources has the potential to reshape energy policy at national and international levels—altering geopolitics and energy security, recasting the economics of energy technology investment decisions, and shifting trends in greenhouse gas (GHG) emissions. In anticipation of this expansion, one of the perceived core advantages of unconventional gas—its relatively moderate GHG impact compared to coal—has recently come under scrutiny. In this paper, we compare the GHG footprints of conventional natural gas, unconventional natural gas (i.e. shale gas that has been produced using the process of hydraulic fracturing, or 'fracking'), and coal in a transparent and consistent way, focusing primarily on the electricity generation sector. We show that for electricity generation the GHG impacts of shale gas are 11% higher than those of conventional gas, and only 56% that of coal for standard assumptions. [But see above.]
 Substitution of natural gas for coal is one means of reducing carbon dioxide (CO2) emissions. However, natural gas and coal use also results in emissions of other radiatively active substances including methane (CH4), sulfur dioxide (SO2), a sulfate aerosolprecursor, and black carbon (BC) particles. Will switching from coal to gas reduce the net impact of fossil fuel use on global climate? Using the electric utility sector as an example, changes in emissions of CO2, CH4,SO2 and BC resulting from the replacement of coal by natural gas are evaluated, and their modeled net effect on global mean-annual temperature calculated. Coal-to-gas substitution initially produces higher temperatures relative to continued coal use. This warming is due to reduced SO2 emissionsand possible increases in CH4 emissions, and can last from 1 to 30years, depending on the sulfur controls assumed. This is followed by a net decrease in temperature relative to continued coal use, resulting from lower emissions of CO2 and BC. The length of this period and the extent of the warming or cooling expected from coal-to-gas substitution is found to depend on key uncertainties and characteristics of the substitutions, especially those related to: (1) SO2 emissions and consequentsulphate aerosol forcing; and (2) the relative efficiencies of the power plantsinvolved in the switch. [Short-term: more warming with shale gas. Longer term: gas beats coal. The exact time horizons seem to be quite sensitive to the initial assumptions, but there seems to be fairly broad agreement about the overall picture, and dissenters -- like "Shell Global Solutions" -- get around these facts by simply ignoring the short-term time frame.]

Coal to gas: the influence of methane leakage
Tom M. L. Wigley

Carbon dioxide (CO2) emissions from fossil fuel combustion may be reduced by
using natural gas rather than coal to produce energy. Gas produces approximately half the amount of CO2 per unit of primary energy compared with coal. Here we consider a scenario where a fraction of coal usage is replaced by natural gas (i.e., methane, CH4) over a given time period, and where a percentage of the gas production is assumed to leak into the atmosphere. The additional CH4 from leakage adds to the radiative forcing of the climate system, offsetting the reduction in CO2 forcing that accompanies the transition from coal to gas. We also consider the effects of: methane leakage from coal mining; changes in radiative forcing due to changes in the emissions of sulfur dioxide and carbonaceous aerosols; and differences in the efficiency of electricity production between coal- and gas-fired power generation. On balance, these factors more than offset the reduction in warming due to reduced CO2 emissions. When gas replaces coal there is additional warming out to 2,050 with an assumed leakage rate of 0%, and out to 2,140 if the leakage rate is as high as 10%.
. . .
In our analyses, the temperature differences between the baseline and coal-to-gas
scenarios are small (less than 0.1°C) out to at least 2100. 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.
This is contrary to claims such as that by Ridley (2011) who states (p. 5), with regard to the exploitation of shale gas, that it will “accelerate the decarbonisation of the world economy”. The key point here is that it is not decarbonisation per se that is the goal, but the attendant reduction of climate
change. Indeed, the shorter-term effects are in the opposite direction. Given the small
climate differences between the baseline and the coal-to-gas scenarios, decisions regarding further exploitation of gas reserves should be based on resource availability (both gas and water), the economics of extraction, and environmental impacts unrelated
to climate change.


So after this whirlwind tour of shale gas research, what do we know? There is no consensus about whether or not substituting shale gas for coal will slow global warming this century. This is not going to be one of those issues where all the science is lined up on one side, and all the partisan kooks are lined up on the other. The exact effect of switching from coal to shale gas depends upon a number of factors that are difficult to pin down, including:

1. The size of the aerosol forcing. After many decades of trying to pin it down, we still do not know exactly how much cooling the SO2 and other coal-burning byproducts are causing. Obviously the effects of switching from coal to gas depend on how much coal-burning byproducts temporarily cool the planet.

2. The amount of methane leakage. This is a function of not just how well we measure methane leakage, but whether we aggressively regulate methane leakage to hold it to an absolute minimum.

3. The discount rate. Not really a physical constant, but more of a philosophical question: how important is relative cooling 300 years from now compared to worsening global warming over the next twenty years (or fifty years, or hundred years)?

4. The half-life of methane in the atmosphere. As far as I know, no one has discussed this relative to the shale gas question, but the oxidization of methane to CO2 by free radicals is subject to saturation, which is the science-y way of saying that the more methane you put in the atmosphere, the longer each molecule stays in the atmosphere:

The magnitude and feedbacks of future methane release from the Arctic region are unknown. Despite limited documentation of potential future releases associated with thawing permafrost and degassing methane hydrates, the large potential for future methane releases calls for improved understanding of the interaction of a changing climate with processes in the Arctic and chemical feedbacks in the atmosphere. Here we apply a “state of the art” atmospheric chemistry transport model to show that large emissions of CH 4 would likely have an unexpectedly large impact on the chemical composition of the atmosphere and on radiative forcing (RF). The indirect contribution to RF of additional methane emission is particularly important. It is shown that if global methane emissions were to increase by factors of 2.5 and 5.2 above current emissions, the indirect contributions to RF would be about 250% and 400%, respectively, of the RF that can be attributed to directly emitted methane alone. Assuming several hypothetical scenarios of CH 4 release associated with permafrost thaw, shallow marine hydrate degassing, and submarine landslides, we find a strong positive feedback on RF through atmospheric chemistry. In particular, the impact of CH 4 is enhanced through increase of its lifetime, and of atmospheric abundances of ozone, stratospheric water vapor, and CO 2 as a result of atmospheric chemical processes. Despite uncertainties in emission scenarios, our results provide a better understanding of the feedbacks in the atmospheric chemistry that would amplify climate warming.
So depending on how widely shale gas is adopted, and on whether other sources of methane such as permafrost melting or methyl hydrates come into play, methane leaks from shale gas could have double or even quadruple the impact on the climate presently assumed.

Given these uncertainties, what can we say with at least moderate confidence?

1. Shale gas is probably worse than coal on the 20 year horizon. Apart from all the other evidence, the determination of shale gas boosters to avoid talking about the 20 year horizon suggests that this is the case.

2. There is a time horizon out there at which shale gas becomes better from a warming perspective than coal. It's just not clear yet whether it is at 25, 100, or 300 years . . . i.e., whether it is soon enough to do us any real good.

3. Shale gas is significantly worse than every other sort of energy except coal and oil. In the absence of a carbon price, cheap shale gas will tend to displace all energy sources, not just coal. Thus a realistic analysis of a Tea Partyesque policy of letting frackers "do their thing" with minimal regulation would compare shale gas to a basket of power sources that would be displaced, including hydro, geothermal, solar, wind, and nuclear, as well as discouraging investments in efficiency or decisions to conserve. Shale gas is unlikely to look good on this basis.

So, can shale gas be a "bridge fuel"? In my opinion, not in the way shale gas is happening right now. To have any hope of a real net benefit in terms of global warming this century, we need draconian limits on methane leakage and a carbon price (including both CO2 and methane) to ensure that shale gas replaces coal, not low-carbon energy sources or improvements in efficiency. The narrative of "the free market slashed CO2 emissions while the enviros weren't looking HAHAHA" has no basis in fact. The blind squirrel of the free market may stumble into an instance of profit-driven accidental mitigation once in a while (like the Russians controlling methane leakage from pipelines after the fall of the Soviet Union), but this ain't it. Similarly the idea that shale gas is an unambiguous "win" in mitigation terms, so much so that those questioning it are self-evidently trolls lurking under "the bridge to the clean energy future" is also not supported by the research.
Sea level rise to 2500. Source.

How we do shale gas is going to determine whether there is a window where there might be some net benefit. Both proponents and opponents of mitigation have tended to stress the 100-year time frame, for different reasons. If you accept that framing, even optimal shale gas substitution is probably going to show, at best, moderate benefits. If you are looking 500 years into the future, shale gas instead of coal is the best thing since sliced bread, but then, if you're looking 500 years into the future,  you can hardly help but realize that stopping all fossil fuel use as soon as possible should be our overarching priority.


  1. True enough, but most of the aerosols from coal are from the sulfur, which produces acid rain, so then you are left with another balancing act. Better to compare coal with soa desulfurization.

  2. Yeah, there are a lot of other negatives to burning coal. The burden of human lung disease is a big'un. I wanted to stay as focused as practicable on the change in forcing with shale gas versus coal.

    Some argue that since we're going to have to clean up the coal anyway, we should just leave the sulfur aerosols out of the equation. Again, though, it all depends on the time frame you think is most important, and if you're anointing shale gas as the "bridge" to clean energy, it seems perverse to ignore the short-term effects.

    IDK, this seems like a really basic question -- does substituting shale gas for coal help delay the arrival of the Eocene Redux? Maybe there is a sharper tool than myself among the bunny legions who would take the problem up?

  3. Re the discount rate: If favoring fracking over coal requires a low discount rate (i.e. high value on the relatively distant future), it would be interesting to know what the rate is that tips the balance to shale. Generally, lukewarmists have argued for a high rate, which supports delayed action. The arguments for a high rate (i) fail to give adequate weight to the downside (possible catastrophe) and (ii) assume that economic growth today produces wealth that will translate directly into better ability to deal with climate mitigation and adaptation tomorrow (e.g., today's infrastructure investments, like multi-story concrete parking structures, will be really useful, somehow). That's dangerous garbage, and any advocacy of lower discount rates in this context should be applauded. The critical questions re: shale then, would not be whether it's better than coal, but this: (1) is the discount rate that tips the choice from coal to shale low enough to be reasonable, or is it still too high? (2) if it is low enough, then at that rate how does shale stack up against conservation & renewables?

    1. "Generally, lukewarmists have argued for a high rate, which supports delayed action."

      Exactly the point I try to get to in the last paragraph. If you're focused on the short-term, fracking is a break-even prospect, at best, but if you take the long view, the things you are seeing in the long view should be scary enough to make you want off this fossil fuel death train.

      "assume that economic growth today produces wealth that will translate directly into better ability to deal with climate mitigation and adaptation tomorrow"

      And the serious problem with that is, should climate change and the political response to it severely disrupt economic growth, we could be left with worsening consequences and a diminishing ability to deal with them.

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