English ecologist Jeffrey Dukes calculated in 2003 that it takes 98 tons of prehistoric, buried fossilized plant material to produce each gallon of fossil fuel that we burn in our cars.1 98 tons to the gallon is poor mileage even by SUV standards. Dukes also calculated that the amount of hydrocarbons burned in fossil fuels each day was equal to the amount of carbon sequestered by all of the plants on earth every year. These measurements hint at the challenges human society will face if it tries to replace fossil fuels with biofuels.

What are biofuels? Briefly, they are liquid fuels made out of recently living organisms, predominantly plants. The primary biofuels are ethanol (made from plant sugars), cellulosic ethanol (made from wood and other plant fibers) and biodiesel (from plant-derived fats and oils). The most common source plants for ethanol are sugarcane, sugar beets and corn. Cellulosic ethanol can be made from wood and fast-growing plants like grass (especially switchgrass). Biodiesel is commonly produced from soybeans (in mid-latitudes) and palm oil trees (in the tropics).

Can biofuels be produced from plants that will run vehicles? Yes, they can. Can biofuels replace all or an appreciable part of the 85 million gallons of petroleum that the world consumes on a daily basis? No, they can’t. Here’s why.

1. Biofuels have a relatively low energy return on the energy that must be invested to produce them (see Getting a Decent Return on Your Investments also posted at www.sustainablemethow.net). This energy return is particularly dismal for corn-based ethanol, which is variously estimated to be between 1:1 (no energy return at all after spending 5 months growing and processing the corn) and 1.3:1 (30% more energy than was invested in growing and processing). Compare this to the energy return on gasoline, which is estimated to have been as high as 100:1 from the early “supergiant” fields” when they were producing freely, and is now between 30:1 and 10:1.

The best current biofuel energy returns are from sugarcane in Brazil and palm oil in Malaysia, both of which are purported to return eight times the energy invested (8:1). However, this ratio does not take into account the degradation of fragile tropical soils from intensive yearly cropping, nor how high production will be maintained once petroleum-based fertilizers, pesticides and herbicides become unavailable, nor the loss of the farmed land to other uses.

2. It is estimated that 40% of the earth’s annual photosynthetic productivity is already utilized by humans, largely for food and building materials, with most of the other 5-20 million species (the actual number is unknown) on the planet making do with the remaining 60%.2 Attempting to produce large quantities of biofuels will rapidly accelerate habitat destruction and the further demise of other species.

3. All of the best cropland on the planet is already under cultivation to produce food. Large-scale appropriation of crops for fuel will unavoidably compete with food production. For example, it is estimated that 20% of this year’s U.S. corn crop will go ethanol production rather than to food for humans or feed for livestock. As Lester Brown of the Earth Policy Institute has pointed out, “The grain required to fill a 25-gallon SUV gas tank with ethanol will feed one person for a year. The grain to fill the tank every two weeks over a year will feed 26 people.” If we turn to large-scale biofuel production, we will have to choose between feeding our cars and feeding human beings.

4. The human population continues to grow at a rate of about 1% a year, which yields a doubling time of 70 years. While almost no one is predicting that the current 6.5 billion people will reach 13 billion (because the number of children per woman continues to drop in most societies, and because there is not enough, food, fuel or water on the planet to support 13 billion people), our numbers are expected to grow to 9 billion by 2050. In addition, energy use in the U.S. and throughout the developed world continues to grow by about 2% a year. If it were possible, we would double our current 85 million barrels of oil used today to 170 million barrels by 2076. Any assistance from biofuel production would be completely overwhelmed by growth in human numbers and increasing energy use.

Do we have other options? Yes. One would be to learn live in the real world. On this particular planet that translates into recognizing that 1) energy is limited, 2) resources are limited, and 3) all habitats and ecosystems have a carrying capacity; if pushed beyond capacity for too long they collapse.

Biofuels could play a meaningful role in a society that lived with some ecological modesty. There is no real long-term option for us other than living by nature’s non-negotiable ecological rules. Nobody argues with gravity, why argue with the simple reality of a spherical, limited-in-all-directions planet? If we want our species and life in general to flourish, we will have to drive less, fly less (or not at all), buy less, build smaller homes, have smaller families, and relearn how to live local, community- and watershed-based lives.

1. Burning Buried Sunshine: Human Consumption of Ancient Solar Energy, by Jeffery Dukes. globalecology.stanford.edu/DGE/Dukes/Dukes_ClimChange1.pdf
2. Human Appropriation of the Products of Photosynthesis by Peter Vitousek, Paul R. Ehrlich, Anne H. Ehrlich and Pamela Matson (1986), dieoff.org/page83.htm.