Once taught that that corn-based ethanol was a cleaner, greener fuel, we soon learned that large-scale production of corn-based ethanol not only had a direct impact on the price of food, life cycle analyses showed that it had a deleterious effect on air quality, water quality and was a net producer of carbon dioxide, the most prevalent heat-trapping greenhouse gas.

So when the federal tax credit for corn-based ethanol expired at the end of 2011, companies began stepping up their efforts to realize one of the holy grails of biofuel:  commercial-scale cellulosic ethanol.

Now, money is flowing into all kinds of new projects, whether they are ready for primetime or not. One of those projects, the Frontier Renewable Resources wood-to-ethanol plant in Michigan's Upper Penninsula, hopes to use a technology designed by New Hampshire-based Mascoma to produce 40 million gallons of ethanol from small-diameter trees annually.

On paper, the project sounds good, but dig a little deeper and the project claims appear  largely unsubstantiated. And since Mascoma, along with Valero Energy, which bought a $132-million stake in the project, will be able to take advantage of a $40 million annual tax credit for their efforts. Deeper digging is prudent. Because while the decades-old ethanol tax credit of 46 cents per gallon did expire at the end of 2011, the cellulosic ethanol tax credit of $1.01 per gallon did not.

Touting the end of the ethanol production tax credit as a win for the environment, the environmental community is largely on board with cellulosic ethanol—ethanol made from woods, grasses and non-edible plant and crop waste. In practice, however, some divisions remain.

In the case of the Mascoma project, for example, which received $80 million in grants and loan guarantees from the U.S. Department of Energy, and another $23 million from the State of Michigan, the Sierra Club has sued to stop the project, charging that the environmental assessment was inadequate and a full Environmental Impact Statement should be prepared.

According to the assessment, 71,000 acres of timber, mostly from the Upper Peninsula, would be harvested annually for the plant if it produces 40 million gallons of ethanol a year. 71,000 is acres roughly 111 square miles. Mascoma says biofuel production could possibly reach as much as 80 million gallons a year  — meaning that 222 square miles of small diameter low-value wood would need to be harvested annually. Sierra Club says the math just doesn't work out and called the numbers into question in comments (pdf) submitted about the Department of Energy's Environmental Assessment: According to the Sierra Club:
•    One-third of the 150-mile radius area that the Mascoma project hopes to harvest timber from is underwater and roughly another third of the land is located in Canada, which brings into question the validity of the project's local job creation claims.
•    Nowhere is there documentation (either in the EA or scientific literature) that 100% of growth can be removed sustainably long term.
•    Over the life of this project (40 years) there will be a net increase in greenhouse gases. That time frame is shorter than that needed to replace 50 million green tons of wood. The project will be removing sequestered carbon faster than it replaces it in the short term.
•    The analysis also fails to account for the greenhouse effects of burning wood, which may include N2O and other compounds which are far more potent greenhouse gases than CO2.
•    The project will consume more energy than it produces:  resulting in a net loss of 1.7 trillion btus of energy.

The issue for environmental organizations like the Sierra Club is not that cellulosic ethanol is inherently bad or environmentally destructive. The problem is that cellulosic is not inherently good or environmentally benign. Feedstock matters, they argue. Just because the ethanol is derived from cellulosic feedstocks does not mean proper environmental analyses can be skipped before projects with federal or state financial backing are greenlit.

Cellulosic biofuels show a lot of promise as a transportation fuel. The Sierra Club understands that. They also understand that a plan to harvest 71,000 acres of timber annually to produce a drop in the biofuel bucket—whether it is "sustainably harvested" or not—may not be the best use of the technology and deserves a longer look. Good money says that the projects and policies that support such projects should be given as much or more scrutiny as those that supported the corn-based boondoggle that finally sunsetted less than two months ago.