CO2 and The Great Ethanol Spreadsheet Mystery
Fermenting sugars and starches to make ethanol produces carbon dioxide. Whether you're a beer or a champaign kind of TreeHugger, this intuitive insight is immediate and obvious. So far the public policy debate about Ethanol's merit has hinged on energy yield "per vehicle mile traveled" (VMT), and on ethanol's ability to add oxygen to the internal combustion cycle, thus reducing carbon monoxide (CO) emissions from the tailpipe. Of course, politicians and the farm lobby throw in some "energy independence" rhetoric, with family farmers in the backdrop. Not much about climate change impact compared to other fuels. Wonder why that is?A US Department of Energy published study from 1994 (partial excerpt of relevant points shown below) indicates ethanol is roughly equivalent to gasoline in CO2 emitted/VMT. The table's sums are life cycle based, including significant CO2 producing aspects for both ethanol and gasoline. Sounds like an explanation right? Look closely at the table for a real surprise.
According to the table footnote, DOE had assumed, in it's calculation of life cycle CO2 burden, that "sequestration" of the production-emitted CO2 occurs in plants, during photosynthesis. What interpretation can there be but that CO2 is freely let to the atmosphere: a "sky pipe", in other words? [Note: see Update #2 below for clarification.]
Maybe they think we'll assume that there are giant greenouses attached to all ethanol factories, running 24/7?
Mark Twain, often attributed with the popularizing the quip "There are three kinds of lies: lies, damned lies, and statistics", would have been impressed with the 1994 study, were he a Connecticut Yankee in the Beltway Court.
If the -299g/VMT of CO2 were made properly positive, biodiesel and gasoline look relatively better with respect to climate impact, and alcohol not such a great alternative on its own. For perspective's sake, we hasten to point out that burning alcohol in the volumes needed to drive America's transportation infrastructure would emit orders of magnitude more CO2 than present levels of commercial fermentation do. We can't drink ourselves out of this relativism.
Not sure which bio-fuel wins on all counts. Gasoline has its own problems relative to Peak Oil. And, it's possible that the table has since been re-worked or better explained.
If you know of a better DOE or other source, please comment with a link or two. ===== UPDATE #1 =========A most interesting set of comments follow this post. Although there seems to be a general agreement that ethanol as a transport fuel does little to mitigate climate change...this was a major point of the post...objection was made to post's treatment of the sequestration deduction. Criticism accepted. Use of the Mark Twain quote was unfair, for example, as it infers a study flaw or bias that may have been intentional, which is not the case. As the comments below point out, "deduction" in the balance sheet of fermentation emitted carbon dioxide has generally been considered "legitimate" practice for a life cycle inventory study of alternative fuels. On the other hand, climate change presents a high risk challenge that can benefit from a look from new perspectives. We look forward to additional comments, especially, regarding the acceptability of crediting bio-fuel manufacture, but not fossil fuel refining, with sequestration, given that far more carbon dioxide is already present in the atmosphere than can be mitigated by photosynthesis.=====UPDATE #2 ==========Even though ethanol may release a significant amount of greenhouse gas per mile traveled, this can be considered "recycled CO2" which was previously pulled from the atmosphere by corn (or other plants). Burning gasoline, while it may provide more miles per unit of CO2 released, is releasing a formerly buried form of carbon, thus compounding the atmospheric CO2 concentration, rather than simply cycling it in and out. From this point of view, gasoline compounds the problem, while ethanol does not.