Fuel for thought
Both biofuels and fossil fuels rely on plants converting sunlight into stored chemical energy (as in the form of sugar or starch), which is harnessed and then released later. For fossil fuels, this energy release is accompanied by CO2, originally taken millions of years ago by the plants and microbes that then became coal, oil or gas. Carbon dioxide released by biofuels, however, is offset by the absorption of CO2 by the leaves of a biofuel crop recently grown in a field.
Biofuels are also renewable (unlike oil, coal and gas), portable (so important as a transport fuel) and versatile, appearing as many types (including biodiesel, biogas and bioalcohols).
However, if you look at the entire life cycle of biofuel production - from "farm to forecourt" - the costs may outweigh the benefits. Nor is there a set cost for each biofuel. For instance, the Worldwatch Institute made life cycle assessments of US and Brazilian bioalcohol production and found that Brazil's process reduced eight times more greenhouse gases. US reliance on fossil-fuel manufactured fertilisers and pesticides, and fuel-hungry harvesting machines, accounted for this difference.
Costs outside this life cycle include deforestation (as virgin rainforest is cleared for sugar cane fields) and reducing biodiversity, as forest wildlife habitats are also destroyed. "All the biofuels we use now cause habitat destruction, either directly or indirectly," says Joe Fargione of the US Nature Conservancy, who led one of the two separate studies published Science, earlier this year, which demonstrated that, in general, existing, first generation biofuels released far more CO2 into the atmosphere than they absorbed during their growth.
In some cases it would take centuries of growing biofuel crops to pay off the "carbon debt" caused by their initial cultivation. The debt to pay off the conversion of Indonesian peatlands into palm-oil plantations, for instance, would take 423 years.
Accordingly, there is now greater emphasis on developing so-called second generation biofuels, which use organic waste (the woody or fibrous material of food crops that cannot be eaten), or crops that are not grown for food at all, such as switchgrass or Miscanthus. Scientists are working on ways of improving the efficient conversion of this material into biofuels.
Growing Algae, a microscopic plant, on a huge scale as the raw material for third generation biofuels, is another idea, as it can be grown at sea or on marginal land, useless for food production.
While Professor Jean Ziegler, UN special rapporteur on the right to food, has attacked the rush to grow food crops for biofuels as a "crime against humanity", he does believe in the concept. In five years, he said, it should be possible to make biofuel from agricultural waste rather than using soya beans, sugar cane or maize.
If that can be made to work, then the second and third generation biofuels currently being developed could play an important role in helping to solve some of the most pressing environmental problems of the early 21st century.