Biofuels may be partial solution to global warming

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February 16, 2007

5:26 PM

In a world troubled by increasing global temperatures and growing energy demands, many scientists have championed biofuels as a partial solution.

p. The most famous green fuel, corn-based ethanol which is sold blended with gasoline, accounted for almost 3 percent of US automotive fuel sales in 2005. That seemingly insignificant 3 percent is actually 16 billion liters. Despite its growing popularity, corn-based ethanol has been widely criticized.

p. Corn is produced through-high intensity agriculture, enormous monocultures that require fertile soil and high inputs of pesticides and fertilizers. Devoting these resources to biofuel production takes away land from food production. Also, while burning the ethanol in an engine produces less greenhouse gas emissions than traditional gasoline, the amount of energy spent to harvest the corn and refine the ethanol requires burning a sizeable amount of fossil fuels.

p. To address these concerns, a research team from the University of Minnesota has been studying alternative sources of the biomass necessary to create the fuel, replacing the need for crop species by using native grassland plants. Their research, published in the Dec. 8 issue of Science magazine, shows that — when processed into synthetic fules — high-diversity grassland vegetation can produce up to 51 percent more usable energy than corn. This dramatic increase in usable energy was accomplished while growing the grassland plants on degraded, infertile soils with low inputs, while the corn was grown on fertile soil with high-intensity agriculture.

p. The research team experimented with plots of different numbers of randomly selected native species, planted and then left alone to grow over a 10-year period. The biomass production increased dramatically with the increase in the number of species present. These fields can be more productive because the combination of native plants allow them to grow like a natural environment. It doesn’t seem to matter what species are grown, just that the diverse environment encourages the plants to grow more than in a monoculture.

p. There are several methods of converting plant biomass to usable fuels, each with their own energy costs and benefits. Combustion with coal in traditional coal-fired power plants can produce 18.1 GJ of electricity from each hectare harvested. More efficiently, another process integrating both electricity and biodiesel production can yield 28.4 GJ from each hectare of high-diversity, low-input grassland vegetation. Comparatively, corn-based ethanol can produce 18.8 GJ per hectare, and soybean based diesel 14.4 GJ.

p. The scientists attribute the higher net energy yields from the LIHD compared to the corn or soy to three factors. First, the grassland species are perennial and native, in contrast to the annual crop species that require far more attention and costly inputs. Second, their research showed dramatic increases in production associated with high species diversity, while corn is produced in a monoculture. Finally, all of the above-ground vegetation was used in fuel production from the grassland plots, while from corn crops, only the seeds (the corn kernels) are used, but the remaining stalks and leaves are basically waste.

p. Besides their ability to make productive use of the existing infertile, degraded lands, these biofuels have an additional environmental benefit. Production of energy from these LIHD sources is carbon negative. While all fossil fuels release carbon dioxide and other greenhouse gases into the atmosphere (carbon positive) the growing plants in the LIHD fields take more CO2 out of the atmosphere than is produced when the biomass is processed into fuel and transported. Corn and soy, while much lower in emissions than fossil fuels, still have net-positive emissions from the associated agricultural processes and fuel production. The reductions in CO2 provided by these LIHD plants could be very beneficial to the atmosphere, as it is considered a cause of global warming.

p. This new research has global implications. In the Science article, the authors estimate that there are half a billion hectares of abandoned and infertile fields that are producing enough biomass to generate 13 percent of the petroleum and 19 percent of the electricity consumptions globally. Additionally, the growth of native perennials on non-agricultural land acts as a carbon sink, as the plants take the greenhouse gases out of the atmosphere. Using these already degraded land areas productively allows more of the fertile land to be devoted to food production to meet the ever-increasing demands for food, for something as well as energy. Those good-for-nothing fields full of weeds might soon be very good after all.

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