Posted by 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.)
April 12, 2011
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