This second article from The A-Z of Global Warming deals with biofuels, which will undoubtedly be a phrase that will be heard a lot more often over the coming years, but what are they?, where do they come from?, and what is their significance in relation to global warming?

Biofuels can be described as any fuel that is derived from biomass ie living organisms or their metabolic by-products. For example, crops such as corn and dung from living animals

Although there is still somewhat of a scientific debate going on over the advantages of biofuels, it is thought that the main advantage over fossil fuels (coal,oil and gas), is that the burning of biofuels to release energy does not cause a net increase of CO2 levels in the atmosphere. This is because the source of the biofuel, crops for example, have already taken a corresponding amount of CO2 out from the atmosphere during their growth cycle when they photosynthesise. When this occurs, plants/crops release oxygen and retain the carbon to use as energy.

The carbon is then released when the crop is eventually burnt in order to release its energy. As long as new crops are planted in place of the ones that are burnt, there will be no overall increase in the amount of CO2 released into the atmosphere. So, whilst crop based biofuels don't reduce the amount of CO2 in the atmosphere, they are thought to be more or less carbon neutral.

The difference with fossil fuel deposits such as coal is that the coal deposits have been formed in the earth over millions of years and are therefore considered to be energy deposits rather than part of the energy cycle. The burning of fossil fuels on a scale required to satisfy mankind's energy needs, over a relatively short period of time, hundreds of years as opposed to the millions of years it has taken the deposits to form, means that the burning of such fuels, adds considerably to the levels of CO2 in the atmosphere. This in turn adds to the greenhouse gases already present in our atmosphere, and contributes to the warming of the Earth's climate.

Forms of biofuel

Biofuels can either be in solid form or liquid form.

Solid biofuels such as wood or even manure (dried cow dung) can be burnt to heat water which can then be used to power a turbine, which can generate electricity. Liquid biofuels, such as ethanol can be used as a substitute or be mixed with traditional fuels in automobiles.

Biofuel uses

The major benefit however probably comes from liquid biofuel, for the creation of Ethanol or biodiesel. Ethanol, a substitute for fossil fuel based petrol, and biodiesel, which is just diesel made with crops in place of oil which is a replacement for traditional diesel fuel in diesel motor vehicles. Whilst diesel cars are more fuel efficient than their petrol counterparts, biodiesel vehicles produce even less carbon dioxide. Neither are as efficient however as vehicles running on mostly ethanol-based fuels.

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