From wood-burning stoves in Sudan to coal-fired power plants in Pittsburgh, most of the world runs on biomass energy -- energy produced using materials derived from living things. Two fossil fuels, coal and petroleum, supply about 80 percent of the world's energy. In contrast, biofuels -- fuels made from plants or from animal waste -- contribute less than 2 percent of all fuels produced commercially.
Shifting that load to biofuels is becoming increasingly attractive for numerous reasons, starting with environmental concerns. Both biofuels and fossil fuels release carbon (in the form of carbon dioxide or methane) when they're burned to produce energy. The difference is that the carbon in biofuels was only recently removed from the atmosphere by the plants used to make the fuel. (Plants, remember, "inhale" carbon dioxide and "exhale" oxygen.) Thus, putting that carbon back into the atmosphere doesn't throw the balance off too much.
In contrast, the carbon in fossil fuels has been stored there for millions of years. Releasing it into the atmosphere creates an excess, contributing to smog formation and climate change. Also, biofuels emit no toxins, as opposed to the sulfur and mercury released when coal is burned.
The basic process for making biofuel from biomass is similar to how your body turns food into fuel: Heat, enzymes and fermentation bacteria break down complex starches into simple sugars. That's why high-starch food crops like corn and sugarcane are also prime sources of biofuel -- though any crop, and even waste material from food crops, can be used.
Advances in the methods used to make biofuel are adding to its appeal. Manufactured microbes have been shown to speed starch fermentation to create ethanol, making the process cheaper and more efficient. And one experimental method of gasification can convert all of the carbon present into the carbon monoxide needed for fuel, releasing no harmful carbon dioxide waste.
Growing crops to produce energy promises additional rewards. It could revive local agricultural economies and reduce dependence on foreign sources. It could open new markets to existing crops by utilizing by-products and waste materials that are currently thrown away. And some biomass energy crops attract beneficial insects, reducing the need for pesticides.
However, as with any resource, shortsightedness, lack of knowledge and plain greed can derail biofuel's potential for good. On the next page we'll look at some of the challenges to energy-crop agriculture.