Proponents of shale gas extraction are not particularly pleased with the attention drawn this week to a new study in Climatic Change that found widespread development of Marcellus natural gas may actually accelerate climate change rather than slow it down. Unfortunately for them, their primary argument rests on a lack of hard data on 1) the actual greenhouse-warming potential of methane; and 2) how much methane finds its way into the atmosphere during drilling and transmission of natural gas. You can find a good summary of the defense’s case at something called the Marcellus Shale Coalition. And it is unfortunate for them, because most opponents of the industry, and the author of new study, use exactly the same argument.
Let’s face it: this is pretty critical. The potential reserves of natural gas in the Marcellus Shale, which underlies a good portion of the U.S., mean that they could, in theory, replace much of the conventional fossil-fuel industry in the country. Vast amounts of money are at stake. But more importantly, so is the future of America’s contribution to global warming. We need to know answers to both questions.
Industry has been loathe to supply answers. Money is being made now, political inertia is largely in its favor (although the threat posed from perceived or real problems of water contamination is growing) and so the risk to the industry if the answers do not come out in their favor is enormous.
So in absence of better numbers, it would be useful to take a look at the implications if industry is right, if the Howarth approach grossly exaggerates the greenhouse warming potential, and if industry is actually much better at minimizing fugutive emissions, what can we conclude?
I wrote about some of the basic science here. The take-home message is that burning natural gas, as a replacement for coal, has only half the effect on the atmosphere. It has about 70% the effect compared with oil and its transportation fuel products. But the effects of methane itself, not burning it, are more tricky. When vented directly in the atmosphere it has at least 20 times the effect of CO2, which the problematic product of combustion. Those are numbers about which there is general agreement, assuming we’re talking about the effects averaged over 100 years.
Given the need to reduce carbon emissions to at least 20% of current values — and probably more like 0 — within the next 30 years, does switching to natural gas make sense? Yes, the proponents argue, if you assume it is only a “bridge” fuel that buys us time to development genuinely clean alternatives (wind, solar, fusion, etc.).
But, goes the argument for the people, the real greenhouse warming potential (GWP) should be measured over a shorter time span because if it’s significantly higher, then the induced warming could trigger more greenhouse-gas release (from the permafrost, for example) and push the planet’s ecosystem over a tipping point, after which it doesn’t really matter what methane’s effect is. And again, there is widespread agreement that most of methane’s effects on the atmosphere are felt in the first few decades.
Over 20 years, when interactions with aerosols are considered, the effect may be as high as 105 times that CO2. Let us assume, for the sake our best-case argument, that things aren’t as bad as generally thought, and we have more time to act before triggering positive feedbacks in the permafrost. Add a couple more decades to our horizon and the GWP methane falls to just 50 or thereabout.
So then the question becomes, how much methane can we afford to vent directly into the air before the benefits of burning nature gas are no longer significant?
If the end GWP is close to half that of burning coal, then it might make sense as a bridge fuel. But 50% is only possible if fugitives emissions are close to zero, which they’re not. I would argue that anything over 67% makes the benefits marginal, given the timeframe at our disposal. In other words, if switching to natural gas only gets us no more than 33% reduction in emissions, it’s not worth the many billions of dollars the transition will cost. We can argue about that number, but I doubt anyone would say it’s worth it if the savings are anything lower than 25%. So let’s be as generous as possible and say total natural gas emissions can be as high as 75%
So how high can the figure for fugitive emissions be? The math is simple:
CO2 emissions of burning methane + (relative GWP of methane over 50 years x fugitive emissions) = Emissions relative to burning coal
Turning that around
(Target emissions – emissions relative to coal)/relative GWP of methane over 50 years
= Max fugitive emissions
(75-50)/50 = 0.5%
If industry can keep its fugitive emissions (or “lost and unaccounted gas”) down to one half of one percent of what is delivered and burned, then maybe, just maybe, we can afford to drill for the Marcellus Shale gas. If you think that’s even remotely likely, well, be prepared for a lot of debate.
Or, we could exercise reasonable caution, and assume that fugitive emissions will probably be 2 or 3 times that much, at best. Probably a lot more. We could also not count on an extra couple of decades of breathing room, because, well, the science doesn’t support that. Again, we’re back to the uncertainty of the science. Does it really make sense to assume that all the unknowns are going to work out in industry’s favor? I, for one, don’t like the odds.
Howarth, R., Santoro, R., & Ingraffea, A. (2011). Methane and the greenhouse-gas footprint of natural gas from shale formations Climatic Change DOI: 10.1007/s10584-011-0061-5