Biofuels can offer the potential to reduce greenhouse gas emissions because the carbon content of the plant matter from which biofuels are produced comes from the carbon dioxide absorbed by the plants from the atmosphere during their lifetime. This is in contrast to the carbon in fossil fuels which has been locked up under the ground for millions of years, and which is released into the atmosphere as carbon dioxide when the fuels are burnt.
At their best biofuels can lead to significant savings compared with fossil fuels, however the greenhouse gas emission savings are not 100% for several reasons. Firstly, carbon savings are partially offset by the energy that is needed for cultivation, harvesting, processing and transportation of biofuels. This can represent a substantial fraction of the total energy released from processed biofuels, and varies significantly between different crops. In the worst case scenario, the production process may actually take more energy than can be redeemed when the biofuels are used, completely undermining any possible environmental benefits. Secondly, there may be carbon emissions associated with changing the usage of land to biofuel crop cultivation. For instance, if areas that have not been previously cultivated, such as forest land, are converted to produce biofuels then there may be very significant immediate releases of carbon stored in the existing plant life and in the soil. These land use change effects may prevent biofuel plantations from generating an overall reduction in carbon emissions until many decades of crops have been produced. This is why the RFA is insisting that suppliers report on the sustainability of their biofuels, and will be carefully investigating the overall effects, both direct and indirect, of biofuels production.