In 2004, the USDA came out with a study (PDF) claiming that corn-derived ethanol delivers 67 percent more energy than it consumes in production.

For many observers, including green-minded ethanol critics, the study delivered a resounding “case closed” to the decades-long debate about corn ethanol’s “energy balance.” Critiques began to focus more on the mounting environmental depredations of industrial-scale corn production.

But a study released by MIT — the press release of which was ably skewered on Gristmill last week by Ron Steenblik — to my mind reopens the net-energy debate.

First, a bit of context.

For years, as a series of studies has emerged crediting corn ethanol with positive energy balance, one major critic has clung to the opposite assessment: Cornell University professor emeritus David Pimentel (along with sometime collaborator Ted Patzak of Cal-Berkely).

Pimentel, whom I recently interviewed for Grist, began studying the question as a USDA consultant in the late 1970s.  

Since then, Pimentel has come out with study after study claiming that when all of the inputs to corn-based ethanol are added up, the fuel is an energy bust: Producing it consumes more energy than the fuel delivers.

Pimentel’s contention, if true, is devastating to corn-based ethanol’s advocates: After 30 years of steady and generous government support, corn ethanol still isn’t providing fossil-fuel conservation.

The common response to Pimentel’s heresy is summarized over on the greenie site Journey to Forever: Pimentel is a crackpot who gets his results by relying on out-of-date input numbers.

Interestingly, Pimentel’s work got an endorsement from an unexpected source: the recent MIT study, which as Steenblik’s post shows has to perform rather tortured gymnastics to find value in corn-based ethanol.

The MIT press release summarizes researcher Tiffany Groode’s research thusly:

Based on her “most likely” outcomes, she concluded that traveling a kilometer using ethanol does indeed consume more energy than traveling the same distance using gasoline.

Nor does Groode parrot the Pimentel-relies-on-ancient-data line. Here’s how the the press release quotes her:

The results show that everybody [including Pimentel, mentioned by name] is basically correct … The energy balance is so close that the outcome depends on exactly how you define the problem. [my emphasis]

This is precisely what Pimentel has long argued: that most ethanol energy-balance studies omit key factors like the energy required to manufacture farm equipment.

In our interview, Pimentel told me that his methodology is consistent with life-cycle net energy studies of other fuels. I’m not competent to comment on the accuracy of that statement, but the MIT researcher doesn’t challenge it.

So if Pimentel is essentially right about corn-based ethanol’s negative energy balance, how does Groode wind up tepidly supporting it?

She says what’s known as the “co-product credit” — the energy-saving value of distillers grains, an ethanol by product that can be fed to livestock — pushes ethanol’s energy balance into positive territory.

Incidentally, Pimentel told me he does account for distillers grains, but finds that other researchers tend to overestimate the energy they save.

Again, I’m not competent to comment on this point, but I can say this: The MIT study is telling us that the entire case for corn-ethanol as a net saver of fossil fuel rests on a product — distillers grains — whose only market is industrial meat producers.

That group operates under a kind of bizarro triple bottom line: it profits by generating social, environmental and animal-welfare horror.

Indeed, the FAO recently declared that feedlot meat production spews out more greenhouse gases globally than cars!

Distillers grains as cheap feed for the CAFO industry, it seems to me, represents a thin reed on which to hang the green case for corn ethanol.

Might it be time to take a fresh look at Pimentel’s work?