Hmm, the latest review of studies on corn ethanol concludes that its carbon intensity is about 40% lower than that of gasoline. If true, then ethanol's obviously not a carbon neutral fuel, but it's also not *worse* than gasoline as I've sometimes read: https://iopscience.iop.org/article/10.1088/1748-9326/abde08

One surprise is that they conclude the indirect land-use effects of diverting corn to ethanol are fairly low (i.e., effects from spurring people elsewhere to clear more land for farms). Here are the studies they review — I don’t fully understand why the variation is so high.

Anyway, this paper's just an estimate, it's not an argument for (or against) using corn ethanol indefinitely. For one, it doesn't look at opportunity cost — are there better ways to clean up cars and free up all that land for more sustainable purposes? *That’s* a key question.

(In general, debates around biofuels or ag policy should consider opportunity costs. The world only has a finite amount of land for food, energy, forests, conservation, etc. WRI does a lot of work here—they’re not fans of crop-based fuels for this reason: https://nytimes.com/2018/12/05/climate/agriculture-food-global-warming.html)

Following up, this is a really great thread getting into the guts of this study and carbon intensity estimates for ethanol more generally: https://twitter.com/scianalysis/status/1355961323327082499