And speaking of using natural gas for transportation (as in part of my earlier post, The true face of shale gas), there’s the whole nasty issue of leaks.
Natural Gas May Be Worse for the Planet than Coal:
This week the U.S. Congress heard testimony supporting a bill that would push to replace diesel with natural gas in heavy vehicles. It’s an attempt to cut oil imports, and at the same time reduce greenhouse gas emissions. Part of the argument is that natural gas is substantially cleaner than diesel, and results in the emission of about 25 percent less greenhouse gas.
But experts are warning that natural gas might not be as clean as it seems.
In fact, using natural gas rather than diesel in vehicles could actually increase climate change, says Robert Howarth, professor of ecology and environmental biology at Cornell University. “You’re aggravating global warming more if you switch,” he says.
Howarth is basing his conclusion on a preliminary analysis that includes not only the amount of carbon dioxide that comes out of a tailpipe when you burn diesel and natural gas, but also the impact of natural gas leaks. Methane, the main component of natural gas, is much more effective at trapping heat than carbon dioxide, so even small amounts of it contribute significantly to global warming. When you factor this in, natural gas could be significantly worse than diesel, he says. Using natural gas would emit the equivalent of 33 grams of carbon dioxide per megajoule. Using petroleum fuels would emit the equivalent of just 20 grams of carbon dioxide per megajoule.
Howarth goes further, suggesting that natural gas could even rival greenhouse gas emissions from mining and burning coal–the dirtiest of fossil fuels. He says it’s “not significantly better than coal in terms of the consequences of global warming” and is calling for a moratorium on extracting natural gas from shale, which requires more energy (and so emits more greenhouse gases) than extracting it from conventional natural gas sources.
Oops.
To hang some numbers on the magnitude of current methane leaks, see the US Dept. of Energy’s report, Emissions of Greenhouse Gases in the United States 2007 [PDF] which shows (page 5) that the top three sources of methane emissions in the US are:
So, in addition to those existing leaks, add in tens of millions of new vehicles and connectors (since many people will likely use in-home refueling gizmos), and you suddenly have the potential for vastly larger impact. While Howarth’s analysis is still “preliminary”, I suspect now that he’s opened the door, a lot of people will be rushing through, calculators in one hand and a list of assumptions in the other.
Stay tuned.
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April 16th, 2010 at 4:12 pm
Oops — I just realized that the 2008 version of the document is available.
Home page: EIA - Emissions of Greenhouse Gases in the U.S. 2008-Overview
April 16th, 2010 at 6:46 pm
Oh dear, there’s always the yang.
Excellent interview of Bill McKibben on CBC…
Pt 3: Tough New Planet: Author Bill McKibben has good news and bad news.
http://www.cbc.ca/thecurrent/2010/04/april-15-2010.html
April 19th, 2010 at 1:10 pm
Howarth makes some questionable assumptions about the relative emissions from NG production and transport compared to coal production and transport. In particular, the assumption that production and transport emissions are 33% of combustion emissions is quite high. Initial development of the infrastructure will certainly raise the percentage in the near term, but over time, it’s quite unlikely that such a level of energy overhead would be maintained. Even if that energy overhead is required, it’s unlikely that the analogous overhead for petroleum would remain as low as it is now, as the energy required for production and transport will only grow over time.
His calculations of the global warming potential due to leakage also seem to be a bit off. The easiest calculation is on a per-mole basis, assuming that natural gas is entirely methane (a bit off, but not a lot). 1 mole of methane at the well head will either escape via leakage or be burned to form CO2. We’ll also assume that CH4 has a GWP of 25 (CO2 = 1 by definition). If L is leakage, then the GWP from combustion is 1-L, and the GWP from leakage is 25L on a molar basis (same is true from an energy basis). So for the CO2e from combustion to equal the CO2e from methane leakage, 1-L = 25L, or L = 1/26, which is about 3.8%. Based on DOE natural gas production estimates and EPA GHG emission estimates, a 3% leakage rate is not unreasonable, but Howarth’s numbers don’t quite add up, at least given the explanation as presented.
Whether these all add up to the conclusion that natural gas is worse than coal remains an open question. It’s certainly no panacea, but the analysis does seem to be somewhat lacking in its rigor.
April 21st, 2010 at 6:17 pm
Readers of the Cost of Energy blog may be interested in today’s feature on telegraph21 (telegraph21 is a new, online video magazine) which is an excerpt from
Haynesville: A Nation’s Hunt for Energy. This documentary examines the impact of the recent discovery of Louisiana’s “Haynesville Shale” (the largest natural gas field in the United States) on America’s energy future, and also upon individuals in the Haynesville community.
Please feel free to embed our video on your site or post a link:
http://www.telegraph21.com/video/haynesville-a-nation%E2%80%99s-hunt-for-energy
Thanks!