Better carbon savings: biofuels or trees?

16th January, 2008

Carbon-free transport fuels present some of the most difficult problems in adapting to a low carbon economy and, while there are solutions like hydrogen in the offing, it will probably be 30 years or more before the bulk of fossil transport fuel can be replaced.

Liquid biofuels offer a superficially attractive option because they can substitute fossil fuels more or less directly in internal combustion engines and use the existing fuel distribution system.

Unfortunately, the rush into biofuels appears to be driven more by political expediency than by a critical analysis of their environmental impact and alternative strategies.

Because agriculture and production of biofuels itself uses fossil carbon (for fertilisers, fuels and buildings), the use of these fuels spares only a proportion of the emissions of the fossil fuel equivalent. After taking into account the fossil inputs, bioethanol and biodiesel can still give useful net carbon dioxide emission reductions compared with the use of fossil fuels of between one third and two thirds1,2,3. Depending on the crop, 500- 8,000 litres of fossil fuel equivalent can be produced per hectare, though because of the fossil carbon costs of producing and converting the crop and the non-carbon dioxide greenhouse gases, particularly nitrous oxide4, only an uncertain fraction of this represents avoided emissions.

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