It was in Bill McKibben's first, and arguably best, book, The End of Nature, that I first came across the challenge posed by fugitive emissions. Back then -- just 20-some years ago -- natural gas was touted as a cleaner alternative to coal and oil because the combustion of its primary constituent, methane, results in markedly fewer CO2 emissions than other fossil fuels.
That argument is being made even more forcefully now. Everyone and his or her dog is touting the advantage of converting coal mines and car engines to natural gas as a way to mitigate global warming, as well as reduce oil imports and bolster domestic industry. But McKibben's caveat has stuck in my head ever since. He wrote that you have to also take into account the greenhouse-warming potential of methane that escapes during the extraction and transmission of natural gas. Getting a grip on how much of these fugutive emissions amount to isn't easy -- I tried unsuccessfully despite much effort to get one of Canada's largest natural-gas pipeline operators to provide numbers a few years back -- but McKibben provided estimates of 2 to 3 percent, citing a study from the University of Minnesota.
If you do the math, you find that it doesn't take much escaping methane to cancel out the benefits of burning natural gas compared with coal or oil. Burning natural gas produces half the CO2 as burning coal, but methane has 20-25 times the warming potential as CO2. To take the most conservative case: 50% + (2% x 20)=90%. Tinker a little with the numbers and it doesn't take much to conclude, as McKibben did that:
Switching to natural gas may have no effect. It might even make things worse.
That was in 1989. Now read this, from a draft of an April 2010 analysis by Robert W. Howarth of Cornell University:
A complete consideration of all emissions from using natural gas seems likely to make natural gas far less attractive than oil and not significantly better than coal in terms of the consequences for global warming.
Things are actually worse than McKibben thought. Calculating the warming potential of methane isn't all that straightforward. It's not just a matter of molecule-for-molecule. One has to take into account atmospheric residence time. This explains why estimates you come across tend to vary, usually from 20 to 25. According to Howarth, the figure of 25 refers to the total effect over 100 years, which seems like a fair enough period. But in the short term, say 20 years, the effect rises to 72 times. And two decades is actually a more useful time frame to consider, because we have to try to keep the Earth's climate in check to avoid setting off positive feedback loops that let the warming runaway with itself, and render the longer-term effects less relevant.
So if, as the lowest reasonably possible rate of fugitive emissions is 1.5%, then the total greenhouse effect of natural gas use is probably more than 158% that of coal and closer to 180% that of oil.
The actual rate of fugutive emissions could be, and likely are, a lot higher. A rate of 1.5% assumes industry is doing a good job fixing leaks in pipelines and capturing all the gas from fracking operations. They may be closer to the range of 3.6 to 7.9 for the shale gas industry, making the real warming potential several hundred percent that of coal.
Industry, of course, dismisses these calculations. At least they do when talking with the New York Times. But other studies also suggest that, at best, natural gas isn't a significant improvement on coal or oil when it comes to mitigating greenhouse gas warming. MIT's Technology Review sums it up this way:
... there is a benefit from switching to natural gas, all told, but it might not be worth the cost or the hassle. Making more efficient gasoline and diesel vehicles might work better, and be a faster way to reduce greenhouse emissions, it suggests.
We'll have to wait for more peer-reviewed papers to settle the question of just how poor natural gas really is as a climate-change mitigating option. [Update: here's Howarth's new paper in Climatic Change.] But it seems clear that even in the best-case fantasy scenario, the advantages are marginal. And we can't afford marginal. Howarth concludes that:
... until better estimates are generated and rigorously reviewed, society should be wary of claims that natural gas is a desirable fuel in terms of the consequences on global warming. Far better would be to rapidly move towards an economy based on renewable fuels. Recent studies indicate the U.S. and the world could rely 100% on such green energy sources within 20 years if we dedicate ourselves to that course.
(Among those recent studies are a couple by Jacobson and Delucchi, about which I have written more than once. So let's not dive into the old "but renewables aren't up to the task" argument.)
There's a typo:
50% + (2% x 25)=90%
I think you meant "50% + (2% x 20)=90%"
Yes, Thanks. Working too fast again.
The argument may be correct, as far as it goes. But burning NatGas also doesn't emit Hg or Th, or a host
of other noxious substances.
Yea but ... Burning natural gas off oil wells can't be as good as burning the same natural gas for a purpose. Ever flown over Libya? Gas fires as far as you can see all night (probably not any more ... must be all burned off by now).
"Burning natural gas produces half the CO2 as burning coal"
Does that mean you can get as much energy from burning half as much CH4?
Wish I had stayed awake more in chemistry class....
Is that because more of the energy comes from oxidizing the hydrogen atoms to water vapor, rather than burning the carbon atom to produce CO2?
Harvesting what will be wasted anyway and using it makes sense. But building up a whole new infrastructure to use it in freight transportation sounds like it's gonna take more than just what they vent from oil wells.
And Riman Butturburr,
Yes, that's right. That also gets at the reason we don't get as much energy from burning ethanol. The presence of oxygen in the molecule means that some of the oxidation has already happened.
You've linked to an April 2010 draft, not a 2011 draft.
Further, there's actually a fair bit of literature on the topic already (don't have the papers on hand because I'm out of the office). None of them use a 20-year GWP when comparing coal and gas. Howarth had originally used the 20-year GWP because that's the timespan shale-gas fields will be developed on, which is wrong methodology, BTW (choosing your GWP depends on how far down the road you want to look, not what the activity right now is -- we don't look at auto emissions over 20 years because that's the lifespan of a car).
Now, Howarth does have a paper on the topic submitted to a journal (I don't know which one) and he's made some changes (including adding the 100-year GWP estimate). His 7.9% estimate is probably really, really high (I read somewhere that he used 5% leakage in pipelines and compressor stations as based on European pipelines -- that's very likely from a paper that looked at Soviet pipelines, which were notoriously bad and hardly comparable to North American ones).
Still, should his paper get accepted and published, I look forward to reading it.
Many coal mines emit CH4 too. Right now, that is all vented to the atmosphere. Recovering it to burn would be a big improvement.
I read somewhere that he used 5% leakage in pipelines and compressor stations as based on European pipelines
How is it possible to measure methane leakage?
I had wondered whether methane leakage might make natural gas an environmentally bad source of energy.
We'll have to see if this paper gets debunked, though. It may be one of a wide variety of estimates, and this one is getting attention because it's surprising.
Apparently the EPA's estimate for methane leakage, although it was raised, still makes natural gas cleaner than coal http://www.propublica.org/article/natural-gas-and-coal-pollution-gap-in…
"How is it possible to measure methane leakage?"
I love the rhetoric in these articles: "natural gas" = good, "methane" = bad, even though it's the same CH4 molecule. And somehow the fact that every CCF of CH4 that leaks into the atmosphere is product that the producer could have sold at a profit escapes everyone. I guess that's the "too cheap to meter" part of the age of abundant energy that we were promised for nuclear power.
As I stated elsewhere:
Problem is, Howarth's study starts off with a doozy of a flaw.
The gas that flows back after fracking and drilling out plugs isn't vented. It's flared. Thus, their estimate of 1.9% of a well's lifetime production being vented to the atmosphere during completions is very likely very overestimated. In the low case, while the CO2 from the flare has its footprint, their total carbon footprint is likely doubled or more than doubled in its direct methane emissions.
I'm surprised that Ingraffea didn't see this (he's an old pro in the oil and gas industry).
I do sympathize with Howarth on how to obtain information with which to do this kind of estimate. Companies hold onto their data with an iron fist and fight every attempt to make them submit more. They say they want policy based on science, but won't release the data with which to support those studies.
Finally, there's how not to respond to something like this. I present the Marcellus Shale Coalition. How can anybody have a fruitful dialog with anybody like this?
Total annual emission of methane in the gas industry of the USA (1992) was 1,4 Â± 0,5% of gross natural gas production in the camp. or more than 8.8 billion m3 per year.
In Russia, only the transport gas loss state monopoly "Gazprom" is about 10% of commercial production