Which do we need most? Food or biofuels? This is the stark choice that faces us if we are serious in our intention of substituting biofuels, e.g. biodiesel, for liquid petroleum fuels, given the scale of agricultural production and the land required to grow enough crops to produce sufficient of the stuff to make any difference. The arguments given for adopting biofuels are the usual one about "security of supply" and more nebulous ones about cutting carbon emissions. The following figures should be considered as indicative, but they lend some sense of scale to what is required.
I have noted before that, currently, around 54 million tonnes (oil equivalent) of petroleum is burnt for use in transportation (including 12 million tonnes for aviation). Then on looking at the DTI figures for 2003, we see that 67.4 million tonnes of petroleum were used in total, so another 13.4 million tonnes is used elsewhere, mostly in industry, which further increases the load that we need to supplant in the interests of "security of supply". The carbon emissions, fuel-for-fuel: biofuel for petroleum, would be similar. So there is no argument favouring biofuels in terms of direct emissions. Because both are burnt, producing CO2, biofuels are not "green-fuels" in this sense. They are "green", however, in that they can be considered as a renewable, since each year a new crop can be grown from which to produce the annual biofuel requirement. It is sometimes argued that biofuel production is "carbon neutral", meaning that in the growth of the crop, CO2 is actually extracted from the air by photosynthesis and other CO2 fixing processes, which offsets the CO2 emitted once the biofuel is finally burnt as a replacement for oil based fuels. (It is not "neutral" in fact, but is thought to absorb the equivalent of 20 - 40% of the CO2 that is finally emitted).
Liquid biofuels are principally of three kinds: biomethanol, bioethanol and biodiesel. Biomethanol can be produced from biomethane or from biomass (wood etc.), and bioethanol by fermenting sugar crops (beet etc.). Biodiesel can be made from e.g. waste chip fat, or other waste cooking oil, or a crop e.g. rapeseed or soyabean can be deliberately grown to provide oil to make it from. A chemical modification is required, of esterification, in which the long chain fatty acids contained in the oil are converted to their methyl or ethyl esters. Since there is only enough waste cooking oil produced to provide about 0.03% of the biodiesel requirement we would need to deliberately grow crops such as rapeseed or soyabean to meet the demand for bio-"oil" for this purpose.
It has been proposed in the U.K. to set aside 500,000 hectares of arable land for biodiesel production. Assuming an average oil production of 2 tonnes per hectare per year, this would yield 1 million tonnes (oil equivalent) of fuel, which is about 1.5% of the U.K. annual total oil demand. If that were stretched to 1,500,000 hectares, then 3 million tonnes of fuel could be extracted, which is about 4.5% of the total petroleum used nationally, nearly enough to supply the 5% additive level of biofuel the E.U. are aiming to put into petroluem fuel by 2010, but that is hardly going to make any difference in terms of "security of supply", nor to carbon emissions. It is estimated that the crop will take-up 20 - 40% (equivalent) of the CO2 emitted when its biofuel product is finally burnt, but even at the upper limit, it is only 40% of 5% = 2%. Since somewhere near a 80 - 90% drop in emissions is called for by 2030, to avert catastrophic climate change, this really is a joke!
What about the amount of available agricultural land that 1,500,000 hectares represents? The total arable land in the U.K. is 65,000 km*2 = 6,500,000 hectares. So this is 23% of that total, which would impose significantly on the amount of land we have available to produce food on. Surely, we want to be "secure" in food production as we do in fuel production, and that grown "at home" is only around 70% of what we consume. To complete the calculation, if we were to go all-out for biodiesel, we would need 33,500,000 hectares which is about five times the total area of arable land we have in the U.K., so even if we grew no food at all, we could still only go as far as substituting for 20% of our increasingly "insecure" fuel supply.
There is more land contained within agricultural holdings, in fact about 16,600,000 hectares and so it might be possibly to fertilise, rejuvenate soil and implement other technical fixes to use more of this to grow crops for fuel production - but we would still need to to use twice as much of even that available total to meet the demand.
The conclusion is obvious, we need to adopt more localised communities supplied by local arable land principally for food production, and in this way cut back our use of transportation and its ruinous fuel requirements by about 90%. If we did make such cuts "at-source", then providing a stable national domestic energy supply in the U.K. using biofuels, does begin to appear in sight. Our only means to supply a secure source of fuel and to reduce greenhouse emissions is to live differently and cut demand, at source, mainly through reducing the use of unnecessary fuel intensive transport.